Summary of professional accomplishments

Transcription

1 Summary of professional accomplishments (załącznik 4) Studies of the photoinduced intramolecular electron transfer process in selected electron donor-acceptor systems Marek Józefowicz Faculty of Mathematics, Physics and Informatics University of Gdańsk Gdańsk,

2 I. Personal data 1. Names and surname Marek Jan Józefowicz 2. Current position Institute of Experimental Physics, Faculty of Mathematics, Physics and Informatics, University of Gdańsk, ul. Wita Stwosza 57, Gdańsk Position: Assistant Professor II. Education and degrees Faculty of Mathematics, Physics and Informatics, University of Gdańsk, PhD Studies 2004 r. PhD in Physics, title of the PhD thesis: The influence of the environment on photophysical and spectroscopic properties of fluorenone and its derivatives Supervisor: prof. dr hab. Janina Heldt The thesis was recognized by the Faculty Board of Mathematics, Physics and Informatics as distinctive Faculty of Mathematics, Physics, University of Gdańsk, MSc Studies 2000 r. MSc in Physics, title of the MSc thesis: The solvent influence on spectroscopic properties of fluorenone and its derivatives Sopervisor: prof. dr hab. Janina Heldt III. IV. Information about thus far employment in scientific units since 2005 Assistant Professor in the Institute of Experimental Physics, University of Gdańsk Teaching assistant in the Institute of Experimental Physics, University of Gdańsk The scientific achievement that provides the basis for commencing the habilitation procedures The scientific achievement resulting from Article 16, paragraph 2 of the Law dated on 14 March 2003 concerning scientific degrees and a title as well as degrees and a title in the field of arts (Dz.U. no 65, item 595 with changes) is the cycle of publications thematically connected under the title Studies of the photoinduced intramolecular electron transfer process in selected electron donor-acceptor systems. 2

3 IV.1 The list of scientific publications that provide basis for the habilitation procedures H.1 M. Józefowicz*, M. Aleksiejew, J.R. Heldt, A. Bajorek, J. Pączkowski, J. Heldt Spectroscopic properties of ethyl 5-(4-aminophenyl)-3-amino-2,4- dicyanobenzoate Chemical Physics 338 (2007) 53 IF(2007)=1.805, IF(2013)=2.028 H.2 M. Józefowicz*, J. R. Heldt, A. Bajorek, J. Pączkowski Red-edge and inhomogeneous broadening effects of the electronic spectra of ethyl 5-(4-aminophenyl)-3-amino-2,4-dicyanobenzoate Journal of Photochemistry and Photobiology A: Chemistry 196 (2008) 38 IF(2008)=2.362, IF(2013)=2.291 H.3 M. Józefowicz*, J. Heldt, J. R. Heldt, M. Aleksiejew, A.M. Iwulska, J. Pączkowski, Determination of first-order molecular hyperpolarizability of EAADCy and EDMAADCy using steady-state spectroscopic data and quantum-chemical calculations Optical Materials 31 (2009) 1894 IF(2009)=1.728, IF(2013)=2.075 H.4 M. Józefowicz*, J.R. Heldt, A. Bajorek, J. Pączkowski Spectroscopic properties of ethyl 5-(4-dimethylaminophenyl)-3-amino-2,4- dicyanobenzoate Chemical Physics 363 (2009) 88 IF(2009)=2.227, IF(2013)=2.028 H.5 M. Józefowicz*, P. Milart, J. R. Heldt Determination of ground and excited state dipole moments of 4,5 - diamino[1,1 :3,1 -terphenyl]-4,6 -dicarbonitrile using solvatochromic method and quantum-chemical calculations Spectrochimica Acta Part A 74 (2009) 959 IF(2009)=1.566, IF(2013)=2.129 H.6 M. Józefowicz*, J.R. Heldt Excitation-wavelength dependent fluorescence of ethyl 5-(4-aminophenyl)-3- amino-2,4-dicyanobenzoate Journal of Fluorescence 21 (2011) 239 IF(2011)=2.107, IF(2013)=1.667 H.7 M. Józefowicz* Fluorescence self and external quenching by aniline of ethyl 5-(4- aminophenyl)-3-amino-2,4-dicyanobenzoate Optics and Spectroscopy 110 (2011) 371 IF(2011)=0.610, IF(2013)=

4 H.8 M. Józefowicz*, A. Bajorek, M. Pietrzak, B. Jędrzejewska J.R. Heldt, J. Heldt Influence of degree of methyl methacrylate polymerization on spectroscopic properties of ethyl 5-(4-aminophenyl)- and 5-(4-dimethylaminophenyl)-3- amino-2,4-dicyanobenzoate Journal of Luminescence 134 (2013) 414 IF(2013)=2.367 H.9 M. Józefowicz*, P. Fita, P. Kasprzycki, J.R. Heldt Excited-State dynamics of ethyl 5 (4-aminophenyl)-3-amino-2,4-2 dicyanobenzoate The Journal of Physical Chemistry A (2013) 117 (2013) 4136 IF(2013)=2.775 H.10 M. Józefowicz*, A. Bajorek, M. Pietrzak, J.R. Heldt Quantum-chemical calculations of the electronic structure of 2-amino-1,3- dicyano-5,6,7,8-tetrahydronaphthalene derivatives Spectrochimica Acta Part A 113 (2013)137 IF(2013)=2.129 H.11 M. Józefowicz*, J.R. Heldt, J. Heldt Experimental and theoretical determination of transition dipole moments of ethyl 5-(4-aminophenyl)- and 5-(4-dimethylaminophenyl)-3-amino-2,4- dicyanobenzoate The European Physical Journal Special Topics 222 (2013) 2373 IF(2013)=1.760 H.12 M. Józefowicz*, A. Bajorek, M. Pietrzak, J.R. Heldt, J. Heldt Substituent and solvent effects on spectroscopic properties of 2-amino-1,3-dicyano-5,6,7,8-tetrahydronaphthalene derivatives Journal of Luminescence 153 (2014) 152 IF(2013)=2.367 * - corresponding author The statements of co-authors of publications that determine an individual input of each of the authors in writing each publication together with the percentage share have been presented in appendix 7. The statement of the post-doctoral student concerning the carried out works as well as the percentage share of the participation in them have been presented in appendix 5. 4

5 IV.2 The presentation of the scientific aim of the above mentioned works and the achieved results as well as their possible practical application Studies of the photoinduced intramolecular electron transfer process in selected electron donor-acceptor systems Introduction The changes in the distribution of the electron density taking place in the result of photoexcitation of the luminescent molecule very often cause that its spectroscopic, photophysical and photochemical properties in excited states differ diametrically from the properties in its ground state. This statement is particularly richly supported by the example of molecules possessing an electron donor (D) and an electron acceptor (A) groups, in case of which the phenomenon of the photoinduced intramolecular electron transfer has been observed 1. The mechanism of this phenomenon has become the subject of a widely spread discussion among many scientific groups, right after the Lippert s discovery of an anomalous fluorescence of DMABN molecule in a polar environment 2. The following years of research into the photophysics of this one and similar compounds brought about a number of hypotheses explaining the mechanism of the examined phenomenon. Among many proposed models (among others Planar Intramolecular Charge Transfer (PICT) 3, Wagged Intramolecular Charge Transfer (WICT) 4, Rehybridization Intramolecular Charge Transfer (RICT) 5, Twisted Intramolecular Charge Transfer (TICT) 6 ) that attempted to explain an anomalous DMABN fluorescence, the most concise and holistic one turned out to be the model assuming the creation of the TICT state proposed by the group led by professor Grabowski. The model created by them assumed the formation of a geometrically new structure of the molecule characterized by the mutual perpendicularity of an electron donor and an electron acceptor parts, yet the state that was formed in the result of this process 1 J. Waluk (Ed.), Conformational Analysis of Molecules in Excited States, Wiley VCH, New York, E. Lippert, W. Luder and H. Boos, Advances in Molecular Spectroscopy, ed. A. Mangini, Pergamon Press, Oxford, K.A. Zachariasse, M. Grobys, Th. von der Haar, A. Hebecker, Yu.V. II'ichev, Y.-B. Jiang, O. Morawski, W. Ktihnle, J. Photochem. Photobiol. A 102 (1996) W. Schuddeboom, S. A. Jonker, J. M. Warman, U. Leinhos, W. Kühnle and K. A. Zachariase, J. Phys. Chem., 96 (1992) F. D. Lewis, B. Holman, J. Phys. Chem. 84 (1980) K. Rotkiewicz, K.H. Grellmann, Z.R. Grabowski, Chem. Phys. Lett. 21 (1973) 212 5

6 has been called the TICT state. It should be clearly stated in this place that a detailed study of literature unanimously points to the fact that discovering the mechanism of the phenomenon of an electron transfer of a relatively simple and seemingly model compound, which DMABN is, still causes a great deal of interest and controversies among photophysicists and photochemists 7. The latest works by Catalan point out that in the case of the DMABN compound that is in a strongly polar solvent, the charge transfer state can be achieved in a classical way, i.e. in the result of the S 1 (LE)S 1 (ICT) process which describes the population of the intramolecular charge transfer (ICT) state from the locally excited (LE) state (in accordance with the TICT model), as well as in the result of a direct excitation of the molecule to the S 1 (ICT) state, which is possible with the assumption that the examined compound in its ground state is represented by the collection of conformers with a different angle between a donor and an acceptor groups. In light of the presented information, one can completely understand the fact that the development of the research into the photochemistry and photophysics of various organic compounds possessing in their compound electron donor and electron acceptor parts has been very intensive for the last several years. Among this research, one of the most current scientific issues concerns the mechanism of the phenomenon of the photoinduced intramolecular electron transfer in bichromophoric, donor-acceptor aromatic systems. Such compounds, to which one can include the biphenyl derivatives described in the following sections, very often show extraordinary luminescence properties (these are, among others, a great Stokes shift, an anomalous fluorescence, an inhomogeneous broadening of absorption and emission bands). What is more, spectroscopic and photophysical properties of these molecules strongly depend on the microenvironment in which they are, which makes them perfect to be used as luminescent (spectroscopic) probes 8. Simultaneously to luminescence (spectroscopic) research, bichromophoric D-A systems are the object of systematic studies connected with a broadly understood molecular 7 J. Catalán, Phys. Chem. Chem. Phys., 15 (2013) 8811 J. Catalán, Phys. Chem. Chem. Phys., 15 (2013) J. Catalán, Phys. Chem. Chem. Phys., 16 (2014) 7734 K.A. Zachariasse, Phys. Chem. Chem. Phys., 15 (2013) M. Cui, M. Ono, H. Watanabe, H. Kimura, B. Liu, H. Saji, J. Am. Chem. Soc., 136 (2014) 3388 J. Pączkowski, Fotochemia polimerów. Teoria i zastosowanie, Wydawnictwo UMK,

7 electronics, mostly because of their potential non-linear optical (NLO) properties 9. As it has been known, possessing by a molecule the charge transfer state is an extremely important condition influencing the increase in a non-linear optical response of an examined compound. Summing up, one can state that a systematic research into various photophysical and photochemical processes taking place in a luminescent compound, possessing an electron donor and an electron acceptor parts and a solvent seems an extremely interesting issue not only from a purely theoretical point of view (i.e. comprehending the mechanisms of processes taking place in an examined compound as well as explaining the mechanisms of interaction between examined compounds and their environment) but also because of the possibility to use them as a fluorescent probes or also as materials having non-linear optical properties. In light of the above mentioned information, the experimental and theoretical research done by me (described in the following sections) aims at linking purely theoretical aspects with application ones. Despite many works carried out by world famous authorities in the field of photophysics and photochemistry, the solvation effects and their influence on the phenomenon of the electron transfer in examined by me, newly synthetized D-A systems, still have not been explained. This is why the major aim of the selected group of works (12 publications) was the recognition of spectroscopic, photophysical and photochemical properties of the selected bichromophoric donor-acceptor compounds (biphenyl derivatives, scheme 1) in which we observe the process of photoinduced intramolecular electron transfer and which are also extremely interesting because of quaint application possibilities (i.e. molecular sensors (probes), materials with non-linear optical properties). The examination carried out for the first time for the examined group of compounds with the use of the steady-state spectroscopy (the measurement of the absorption spectra in a gas phase and a liquid environment, excitation, fluorescence and phosphorescence) and a timeresolved spectroscopy (the measurement of the fluorescence decay time, time-resolved 9 C.R. Moylan, R.D. Miller, R.J. Twieg, K.M. Betterton, V.Y. Lee, T.J. Matray, C. Nguyen, Chem. Mater., 5 (1993) 1499 G.U. Bublitz, R. Ortiz, C. Runser, A. Fort, M. Barzoukas, S.R. Marder, S.G. Boxer, J. Am. Chem. Soc., 9 (1997) 2311C.B. Gorman, G.H. J. VanDoremaele, S.R. Marder, Optimization of Materials for Second-Order Nonlinear Optical Applications, Molecular and Biomolecular Electronics, Chapter 8 (1994) 179, Advances in Chemistry, Volume 240 7

8 emission spectra, the measurement of transient absorption) as well as quantum-chemical calculations done by me using CAChe WS 5 programme aimed at: The full comprehension of relaxation mechanisms of the excited states in EAADCy and EDMAADCy molecules, including the recognition of the dynamics of photoinduced processes for EAADCy molecule as well as the definition of an acceptor s role in the process of deactivation of the excited states (Section 1). The estimation of physical-chemical constants that characterize the examined D-A compounds and describing both the influence of a substituent as well as a solvent on designated quantities (Section 2). The assessment of possibilities for application the examined D-A (EAADCy and EDMAADCy) systems as fluorescent probes for monitoring the polymerization process (Section 3). The assessment of possibilities for application EAADCy and EDMAADCy molecules in quantum electronics by estimating their non-linear optical properties (establishing the value of molecular hyperpolarizability) (Section 3). The specification of relations between the structure (systematically introduced modifications) of newly synthetized compounds and their photophysical and spectroscopic properties (Section 4). 8

9 O H H H O OC 2 H 5 H 3 C N H H H OC 2 H 5 CN H 2 N CN H 3 C H H NC NH 2 H H NC NH 2 EDMAADCy EAADCy DTD Scheme 1 Chemical structure of the studied donor-acceptor molecules 1. The studies of relaxation mechanisms of electronic excited states in EAADCy and EDMAADCy molecules Basic and at the same time initial D-A compounds (newly synthetized by collegues from the research group supervised by professor Jerzy Pączkowski, later by profesor Andrzej Wrzyszczyński from the University of Science and Technology in Bydgoszcz as well as by dr Piotr Milart from Jagiellonian University in Cracow) to which the greatest attention has been paid, were two molecules: ethyl 5-(4-aminophenyl)-3-amino-2,4- dicyanobenzoate (EAADCy) 9

10 and ethyl 5-(4-aminophenyl)-3-dimethyloamino-2,4-dicyanobenzoate (EDMAADCy) (scheme 1). The introductory analysis of experimental results achieved by application of the methods of a steady-state spectroscopy (the measurement of emission in various environments and temperatures) and a time-resolved spectroscopy (the measurement and analysis of fluorescence decay curves as well as time-resolved emission spectra) already proves that in the case of examined molecules in a medium polar environment apart from normal fluorescence, i.e. the emission from a locally excited state (LE), also the fluorescence of the conformer that was created in an excited state in the result of the intramolecular electron transfer has been observed (H.1, H.4). What is more, it has been observed that not only the steady-state fluorescence spectra but also time-resolved fluorescence spectra depend strongly on the excitation wavelengths, which together with inhomogeneous broadening of the absorption and emission electronic bands observed for examined molecules in a polar solvent gives evidence that these compounds form a inhomogeneous spectroscopic system already in their ground state (the presence of various conformers induced by a rotation possibility around an single bond between donor and acceptor parts) (H.1, H.4, H.6). Another proof supporting the presence already in the ground state of spatially different conformers in examined D-A molecules were the results of measurements of fluorescence and phosphorescence spectra in solvents forming enamel at 77 K, achieved along with the excitation on an red-edge of the long-wavelength absorption band (H.2). After decreasing the temperature to 77 K, the relaxation time of a solvent (τ R ) becomes comparable or longer than the fluorescence lifetime (τ F ), which is connected with the fact that conformers do not have possibilities to make internal movements and each of them is characterized by its own emission band (fluorescence and/or phosphorescence). It has been proved that shape, intensity as well as location of the fluorescence excitation, fluorescence, and phosphorescence bands of EAADCy dissolved in tertahydrofuran forming enamel at 77 K depends considerably on the excitation wavelength ( red-edge effect 10 ). The complementation and help in interpretation of obtained results constitute theoretical quantum-chemical calculations which were performed using CAChe Pro WS 5 programme (H.1, H.4). Taking the above into consideration, a theoretical conformational 10 A.P. Demchenko, Luminescence 17 (2002) 19 10

11 analysis of the examined compounds has been carried out, it means establishing the internal energy values of molecule as a function of the twisting angle between both chromophores, both in a ground state (S 0 ) as well as in the first (S 1 ) and second (S 2 ) electronic excited states. In the result of calculations, it has been established that the most energetically beneficial conformation in S 0 state corresponds to the situation in which the donor and acceptor moieties are orthogonal to each other ( perpendicular form ). What is more, because of little changes in ground state electronic energy values induced by the twist of surfaces of both chromophores within the range of 60ᵒ to 120ᵒ, both in the case of EAADCy molecule as well as EDMAADCy molecule the achieved results confirm clearly that both examined molecules in the ground state are represented by a group of conformers with various angles between donor and acceptor groups (inhomogeneous spectroscopic system). Additionally, on the basis of obtained theoretical data for examined compounds in S 0 state, with the assumption of the Boltzmann distribution of energy levels, it has been estimated that 33% of EAADCy conformers possess the angle between chromophores between 60ᵒ and 120ᵒ. It should be underlined in this place that a similar regularity, i.e. the fact of existing different conformers in the S 0 state induced by the possibility of rotation between donor and acceptor groups, has been achieved for other examined biphenyl derivatives (H.1, H.4, H.6, H.10). The chemical structure of EDMAADCy molecule suggests that the surface of N(CH 3 ) 2 substituent can take various positions in relations to the surface of a benzene ring (see scheme 1). This concerns both the compound in its ground state as well as in its electronic excited states. The results of quantum-chemical calculations reveal that in the case of EDMAADCy molecule in its S 0 and S 1 the most energetically beneficial conformation is the one in which both chromophores are located towards each other almost in a perpendicular position ( perpendicular form ) but the dimetyloamino group is located in the surface of a benzene ring (H.4). The analysis of the potential energy curve for S 1 and S 2 obtained as the function of a twisting angle between chromophores and in connection with the analysis of the time evolution of emission spectra of examined compounds being in different environments allowed for the proposal of the scheme of energy levels that takes into account conformation changes accompanying the intramolecular electron transfer process. Scheme 2 in a general way pictures the excitation and deactivation paths of EAADCy and EDMAADCy 11

12 molecules being in medium polar solvents (H.1, H.4). The scheme below presents the situation in which light absorption promotes molecule from an equilibrium ground state to the excited Franck-Condon state and next before the emission takes place, a new thermal equilibrium state with the environment is established. In this situation the geometry of the molecule does not change, which can be an indicated by a short-wavelength emission from a locally excited state (emission of conformer where donor and acceptor moieties are orthogonal to each other perpendicular form ). It should be underlined that the longwavelength emission (fluorescence of conformer for which an angle between chromophores equals 45 degrees - flattened form ) is connected with the fluorescence of molecule present in intramolecular charge transfer state. This state can be achieved in the result of the process S 1 (LE) S 1 (ICT) which describes the state population of the intramolecular electron transfer (ICT) state from a locally excited state as well as in the result of a direct excitation of a molecule to S 1 (ICT) state, which already in the ground state is represented by a group of conformers with a different angle between D and A being characterized by a partial charge transfer (see scheme 2). The analysis of experimental data obtained using the steady-state and time-resolved spectroscopy points out that in the case of both examined molecules being in non-polar solvents as well as in strongly polar ones we have to deal mainly with the short-wavelength emission. Additionally, from a detailed analysis of the influence of the twisting angle of mutual surfaces of both chromophores on shapes and energies of major orbitals taking part in transsition between electronic states, it clearly results that this emission (the shortwavelength fluorescence band) is connected mainly with the emission of excited acceptor part of examined D-A compounds (H.1, H.4, H.9). This proves that both examined compounds present in non-polar environments or in strongly polar ones are characterized by a weak coupling between a donor part and an acceptor part, which allows for treating them as two independent chromophores ( composite molecular model 11 ), from which mostly an acceptor part is responsible for emission. 11 M. Maus, W. Rettig, G. Jonusauskas, R. Lapouyade, C. Rulliere, J. Phys. Chem. A 102 (1998) 7393 M. Maus, W. Rettig, D. Bonafoux, R. Lapouyade, J. Phys. Chem. 103 (1999) 3388 M. Maus, W. Rettig, Chem. Phys. 218 (1997)

13 H.O.F. (ev) H.O.F (ev) 6,0 S 1 5,8 S 2 5,6 5,4 5,2 5,0 2,4 I F (SW) I F (LW) 2,0 Abs 1,6 S twisting angle (deg) Scheme 2 Scheme of potential energy curves with double minimum 12 In order to understand fully the mechanisms of processes taking part in this group of compounds, yet research methods with high time resolution, i.e. 200 fs (transient absorption measurements) have been applied (H.9). In the work already discussed (H.9), there have been carried out transient absorption measurements of EAADCy molecule in 5 different solvents with different polarity and viscosity, i.e. dimethylsulfoxid (DMSO), dimethylformamide (DMF), ethyl acetate (EA), tetrahydrofuran (THF), ethylene glycol (EGI). A thorough analysis of the results for the transient absorption measurement, supported with earlier quantum-chemical calculations allowed for the proposal for a new, expanded scheme of photoinduced processes for EAADCy molecule being in a medium polar environment (THF, EA), which also takes into account their dynamics (see scheme 3). In a proposed energetic scheme it has been assumed that light absorption causes transition to the non-equilibrium Franck-Condon state (an early transient absorption spectrum around 440 and 675 nm (see picture 1 in H.9 work)). Before the emission act, a new thermally 12 Taken from: M. Józefowicz, J.R. Heldt, A. Bajorek, J. Pączkowski, Chem. Phys. 363 (2009) 88 13

14 equilibrium state with the environment is established (FC LE process). It should be underlined that at this moment the molecule s geometry does not change and this is why one can observe a short-wavelength emission from a locally excited state, which is mainly connected with the emission of excited acceptor part of EAADCy. On the other hand, the analysis of a signal s kinetics measured at 440 and 505 nm in connection with the presence of an isosbestic point, proving the reaction of a precursor-successor type, gives evidence for the existence of a fast FC ICT NR process, which is connected with a partial electron transfer (the molecule conformation remains unchanged) (H.1, H.4). It should be highlighted that a molecule in this state is not in thermally equilibrium with its environment. Further analysis of the spectral evolution, i.e. the presence of a strong absorption spectrum from maximum around 505 as well as the stimulated emission around 625 nm proves the existence of ICT NR ICT R process (see picture 1 in work H.9). This process is characterized by a complete electron transfer and a molecule being at the beginning in ICT NR moves to the state of complete thermally equilibrium with its environment ICT R, from which the long-wavelength emission occur (the long-wavelength fluorescence band connected with the emission of conformer for which the angle between chromophores is 45 degrees - flattened form ). Finally, a crucial problem solved when analysing transient absorption spectra was the population process of ICT state, which follows from a non-equilibrium Franck-Condon state but never from a relaxed locally excited state that is characterized by a long fluorescence lifetime (nanoseconds). Scheme 3 Schematic representation of the excited-state dynamics of EAADCy in mediumpolar solvents Taken from: M. Józefowicz, P. Fita, P. Kasprzycki, J.R. Heldt, J. Phys. Chem. A 117 (2013)

15 2. Basic physical-chemical constants characterizing EAADCy and EDMAADCy molecules Having gained the knowledge about the relaxation mechanisms of electronic excited states of EAADCy and EDMAADCy molecules, next step to come near a complete knowledge about the examined systems was to establish basic physical-chemical constants characterizing examined compounds as well establishing the influence of the environment on their values. To the most important constants which were established in an experimental way or by means of a quantum-chemical method, we can include: electric dipole moments, transition dipole moments, quantum yields, fluorescence quenching constants or internal and external reorganization energies. It is obvious that there are numerous methods allowing for establishing dipole moments values of molecule in different electronic states. One of them, basing on measurements of locations of maxima of the absorption and fluorescence bands in a gas phase as well as solvents of different polarity, is a solvatochromic method 14. The analysis of locations of maxima of the absorption and fluorescence bands in connection with the knowledge of Onsager radius established with the use of quantum-chemical methods allowed for estimating electric dipole moments in electronic LE and ICT states. Electric dipole moments have been established for the whole group of discussed D-A compounds (including EAADCy and EDMAADCy molecules) (H.1, H.3, H.4, H.5, H.12). It is worth highlighting at this place that in order to estimate the polarizability of examined D-A molecules, there were applied various theories using the Osanger model that describes the solute-solvent interactions proposed by Ooshika, Mac Rae, Bilot and Kawski (quantum-mechanical secondorder perturbation theories) as well as Lippert, Liptay and Bakshiev (a classical description) (H.5). A detailed analysis of the influence of a molecule s polarizability on values of obtained dipole moments has been carried out for DTD molecule. The application of the above mentioned models allowed for estimating the values of 2α/a 3 parameter (where α- molecule s polarizability, a - Onsager radius), which in the case of the examined molecule 14 N.G. Bakhshiev, Opt. Spectrosk. 10 (1961) 717 Y. Ooshika, J. Phys. Soc. Jpn. 9 (1954) 594 E.G. McRae, J. Phys. Chem. 61 (1957) 562 L. Bilot, A. Kawski, Z. Natursorsch. 17a (1962) 621 A. Kawski, Z. Naturforsch. 57a (2002) 255 E. Lippert, Ber. Bunsenges. Phys. Chem. 61 (1957)

16 amounts to 0.4. It must be mentioned that the obtained value is in good agreement with the values proposed by Bakshiev and Kawski 2α/a 3 =1/2 in their theoretical considerations 15. A basic conclusion that results from the analysis of values of the electric dipole moments of examined compounds in S 0, S 1 (LE) and S 1 (ICT) states is that the excitation to ICT state is accompanied with over threefold increase of the dipole moment values, whereas in LE state its value is slightly higher than in S 0. The obtained results are fully comprehensible because the rotation between chromophores resulting from photoexcitation has consequences in a considerable change in the charge distribution, which causes a significant stabilization of flattened form in a medium polar environment. Additionally, in order to explain fully the influence of the rotation of one of chromophores on values of dipole moments in S 0 and S 1 states, quantum-chemical calculations have been done. A detailed analysis of the curve presenting values of dipole moments in an excited state obtained as the function of the twisting angle between both chromophores unequivocally shows an extremely marked increase in the value of this parameter in the case of the conformer for which the angle between chromophores equals 45 degrees flattened form. One should also underline a good agreement between dipole moments values obtained in an experimental way (a solvatochromic method) as well as with the application of quantumchemical calculations (H.1, H.5, H.10, H.12). The base in our possession of experimental data concerning solvation of examined D- A compounds in various environments allowed for the application of Marcus theory 16 to characterize the interaction of a luminescent (EDMAADCy) molecule with a solvent. The H.4 work is devoted to this issue, in which basing on the above mentioned theory, the reorganization energy of an examined molecule, understood as the interaction energy of a luminescent molecule (an oscillator) with a solvent molecules being baths for this oscillator (an outer-sphere reorganization energy) as well as the energy connected with internal molecule vibrations (an inner-sphere reorganization energy) has been estimated. In a situation when EDMAADCy molecule was in a non-polar environment, for which the value of squared refractive index equals closely to a dielectric constant, the value of the outer- 15 A. Kawski, Z. Naturforsch. 57a (2002) R.A. Marcus, J. Phys. Chem. 94 (1989) 3078 B.S. Brunschwig, S. Ehrenson, N. Sutin, J. Phys. Chem. 91 (1987)

17 sphere reorganization energy is close to zero, whereas an average value of the reorganization energy connected with molecule internal vibrations is dominant and equals 0.2 ev. The obtained results concerning the reorganization energy values clearly show that the value of the outer-sphere reorganization energy for a molecule in a locally excited state ( perpendicular form ) and in intramolecular charge transfer state ( flattened form ) differ significantly. Of course, these differences are fully comprehensible because they result from clear distinctions in values of electric dipole moments of both conformers in an excited state, i.e. the increase in a dipole moment, accompanying the reaction of an electron transfer, it evokes the increase in the dipole-dipole interaction between examined and solvent molecules, which in consequence causes the increase in values of the outer-sphere reorganization energy. The act of exciting a molecule by a quantum of light causes usually a great change in the electron density distribution, but the probability of such transition on a time unit is proportional to a squared transition dipole moment between states taking part in a given transition. A basic task which was sketched in H.11 work was estimating the value of the transition dipole moment between states: a ground (S 0 ), a locally excited (S 1 (LE)) and the intramolecular charge transfer (S 1 (ICT)) for EAADCy and EDMAADCy molecules( M, S 0 S 2 S 0 S 1 M, M, M ). Observations of this luminescent parameter in solvents of S 1 S 0 ICT S 0 different polarity (butyl acetate (BA), tetrahydrofuran (THF), dimethyloformamide (DMF)) turned out to be particularly interesting. Basic conclusions following from the analysis of the influence of environment on values of transition dipole moments are: In the case of both examined compounds, the estimated in an experimental way values of transition dipole moments decrease along with the increase in a solvent polarity, which proves a significant influence of microenvironment on probabilities of electronic transition in examined compounds. The values of transition dipole moments between S 0 and S 1 (LE) states, i.e. M S 0 S1 obtained using quantum-chemical calculations are in good agreement with experimental values in a situation when an examined molecule is in a strongly polar environment. The above behaviour is another proof that in the case of an examined compound being in a strongly polar environment, there is a weak 17

18 coupling between a donor part and an acceptor part, from which the latter one is responsible for a emission ( composite molecular model ) Comparing the obtained experimental values M S 0 S 1 as well as M S 1 S 0 estimated for both compounds in all examined environments, the same conclusion can be reached that during the relaxation process of an excited molecule the geometry of an examined compound changes, which can be certified by a difference in obtained values of a transition dipole moments between S 0 and S 1 ( M M ). S0 S1 S1 S0 The complementation to the cycle of works discussing basic physical-chemical constants characterizing EAADCy and EDMAADCy molecules was H.7 work, in which the mechanism of fluorescence quenching in EAADCy molecule was examined, with special attention paid to discovering the quenching mechanism (a static one or a dynamic one), taking into account the spectral inhomogeneity of the emitting system, i.e. considering the fact that deactivation of an excited molecule follows different states that correspond to different molecule s conformations ( planar form and flattened form ). Below, there are major results and observations referring to various aspects of fluorescence quenching (selfquenching (concentration quenching) as well as quenching by an extraneous substance, which in a discussed case was aniline serving also the role of a donor part in an examined D- A system) of EAADCy in homogenous environment, which was THF. The process of fluorescence self-quenching (concentration quenching) is strongly determined by both the structure of an examined molecule (two emitting forms) as well as the environment s temperature, i.e. one can observe extremely strong quenching of a locally excited form ( perpendicular form ) in comparison to fluorescence quenching in a molecule being in ICT state ( flattened form ), both as a function of concentration and temperature. From the research done on the EAADCy+aniline double-component (D-A+D, external quenching by means of donor molecules) it results that both a static (mainly) as well as a dynamic processes of quenching take place for examined compound. 18

19 Taking into account spectral inhomogeneity of an examined compound, it was shown (using a classic Stern-Volmer equation, for estimating fluorescence quenching constants for both emitting forms (k q (LE) and k q (ICT)) that molecules with the donor and acceptor moieties oriented orthogonally are considerable more self and external quenched than the coplanar conformers. 3. Evaluation of application possibilities of EAADCy and EDMAADCy molecules A search for new luminescent probes sensitive to changes of microenvironment properties, caused by the presence, near them, of polymer chain, enjoys a constant popularity, mainly because of a possibility to use such compounds in many modern technologies (modern dental materials, monitoring of the process of varnish coats hardening) 17. Having the above in mind, in order to evaluate possibilities of making use of the studied D-A compounds (EAADCy and EDMAADCy) as fluorescent probes for monitoring of the process of polymerization, their basic spectroscopic and photophysical parameters in the process of thermoinitiated polymerization of methyl methacrylate (MM) (H.8) were defined. The above goal was realized by recording the steady-state absorption and fluorescence spectra, as well as by making measurements of fluorescence decay time and emission anisotropy during MM polymerization. It is obvious that a change in basic luminescence characteristics of the studied probe during polymerization depends on many factors. One, and at the same time the basic factor, is the chemical structure of the studied molecule. Rigid of the surroundings of the studied molecule (an increase in viscosity of the environment) causes a limitation of the possibility of rotation around a single bond between the electron donor and acceptor parts. Moreover, a lack of the rotation possibility causes a decrease in loss of energy through a non-radiative way, which results in an observed increase in fluorescence intensity both of LE band and ICT one. 17 J. Pączkowski, Fotochemia polimerów. Teoria i zastosowanie, Wydawnictwo UMK, 2003 J. Pączkowski, D.C. Neckers, Macromolecules 25 (1992) 548 P. Bosch, A. Fernandez-Arizpe, J.L. Mateo, F. Catalina, C. Peinado, J. Photochem. Photobiol. A: Chemistry 153 (2002) 135 K. Hakala, R. Vatanparast, S. Li, C. Peinado, P. Bosch, F. Catalina,H. Lemmetyinen, Macromolecules 33 (2000)

20 In the discussed work, it was shown that not only in the case of already mentioned solvents creating a glaze in the temperature of liquid nitrogen, but also in the case of very viscous mediums, i.e. during methyl methacrylate polymerization, the solvent relaxation time becomes comparable to the fluorescence decay time, and then the positions of LE and ICT fluorescence bands depend on the excitation wavelength ( red-edge effect ). The results presented in the work prove that a inhomogeneous broadening of fluorescence spectra (both LE and ICT) in MM and dependence of the position of fluorescence maximum on excitation wavelength for EAADCy and EDMAADCy molecules is a result of occurrence of a large differentiation of conformers distribution and local structures surrounding these conformers (spectrally inhomogeneous medium). It should be mentioned that the use of polarization methods explicitly confirmed the existence of differentiation of geometry of the studied molecule. Necessary information was acquired thanks to the possibility of polarization of both the excitation and emitting lights which is connected with recording of fluorescence emission anisotropy spectra and fluorescence excitation anisotropy spectra. The carried out measurements showed that values of fluorescence emission anisotropy and fluorescence excitation anisotropy for both studied compounds, recorded during MM polymerization under conditions of low degrees of conversion are independent of the observation wavelength and are around zero, whereas under conditions of high degrees of conversion we observe a distinct increase in value of fluorescence anisotropy and a significant dependence on the observation wavelength. The analysis of results obtained using time-resolved emission spectroscopy, which allowed us to understand the dynamics of excited states and define processes entangled in it for both studied compounds in the function of MM conversion degree, was a crowning stage of studies aiming at evaluation of possibilities of using the studied D-A compounds as fluorescent probes. To describe the processes accompanying the excitation of EAADCy and EDMAADCy molecules (scheme 4, left column) being in the process of MM polymerization under conditions of high degrees of conversion, as well as to describe radiative and nonradiative deactivation paths (scheme 4, right column) the diagram below was suggested, which takes into consideration the existence, in an excited state, of two main luminescent centers and two modes of light connected with them: the studied molecule, emitting from the locally excited state S 1 (LE) and from the intramolecular electron transfer state S 1 (ICT). 20

21 Both centers emit fluorescence light of different wavelengths, which are characterized by different fluorescence decay time, and the coefficient determining the percentage participation of the given decay component significantly depends on the progress of MM polymerization. M h Abs M M * ICT * LE k 1, k 2 M * ICT M * ICT k ICT F M k ICT IC M k ICT ISC 3 M ICT ICT ICT h ICT M * LE k LE F M LE h k LE IC M LE k LE ISC 3 M LE Scheme 4. A diagram of processes accompanying excitation and deactivation of EAADCy and EDMAADCy being in the process of MM polymerization under conditions of high degrees of conversion 18 A very important conclusion from the studies conducted was the statement that EDMAADCy molecule may be used for monitoring of the polymerization process because of its linear dependence between values of half width of ICT fluorescence band and the time characterizing the progress of MM polymerization. Over the last several dozen years a distinct growth of interest of many research groups in materials with optically non-linear properties (NLO) has been observed 19. Both experimental studies and theoretical quantum-chemical calculations play a very important role in the process of effective and constructive designing of materials having an optically non-linear nature. The presence of the theoretical quantum-chemical calculations is a LE 18 Taken from: M. Józefowicz, A. Bajorek, M. Pietrzak, B. Jędrzejewska J.R. Heldt, J. Heldt, J. Lumin. 134 (2013) C.R. Moylan, R.D. Miller, R.J. Twieg, K.M. Betterton, V.Y. Lee, T.J. Matray, C. Nguyen, Chem. Mater., 5 (1993) 1499 G.U. Bublitz, R. Ortiz, C. Runser, A. Fort, M. Barzoukas, S.R. Marder, S.G. Boxer, J. Am. Chem. Soc., 9 (1997) 2311C.B. Gorman, G.H. J. VanDoremaele, S.R. Marder, Optimization of Materials for Second-Order Nonlinear Optical Applications, Molecular and Biomolecular Electronics, Chapter 8 (1994) 179, Advances in Chemistry, Volume

22 starting point for a rational synthesis of molecules with desirable properties. It should be stressed that a special role in the studies of non-linear optics is played by compounds having the donor and acceptor groups in their molecule, mainly because of having the charge transfer state, whose presence is an essential factor influencing an increase in the non-linear optical answer of the compound studied. In work H.3, selected, non-linear optical properties of EAADCy and EDMAADCy were analyzed with the help of the two-layer model suggested by Oudar and co-workers 20. Within the used formalism based on this model and making use of quantum-chemical calculations it was possible to make an experimental and theoretical assessment of the EAADCy and EDMAADCy non-linear optical answer based on the determined values of molecular hyperpolarizability. Additionally, an application of the mentioned model made it possible to analyze relationships of the molecular hyperpolarizability both as the function of environment and a substituent being an electron donor group. It is worth mentioning here that the obtained values of hyperpolarizability of the EAADCy and EDMAADCy molecules explicitly confirm that the compounds may possess interesting non-linear optical properties, which makes them ideal for use in further studies of non-linear optics. 3. An influence of the environment and a substituent on photophysical and spectroscopic properties of 2-amino-1,3-dicyano-5,6,7,8-tetrahydronaphthalene derivatives It is common knowledge that interactions between a luminescent molecule and the environment surrounding it have an important meaning in physics, chemistry and related sciences 21. It was stressed before, that chemical compounds whose photophysical and photochemical properties strongly depend on microenvironment, are quite commonly used as luminescent probes. The application of a molecule as a luminescent probe requires, however, an earlier determination of its spectroscopic, photophysical and photochemical 20 J.L. Oudar, D.S. Chemla, J. Chem. Phys. 66 (1977) 2664 J.L. Oudar, J. Chem. Phys. 67 (1977) J.R. Lakowicz, Principles of Fluorescence Spectroscopy, Third Edition, Springer (2006) B. Valeur, Molecular Fluorescence: Principles and Applications, John Wiley and Sons (2002) E.M. Goldys, Fluorescence Applications in Biotechnology and Life Sciences, Wiley-Blackwell (2009) 22

23 properties. Having the above in mind, in works H.10 and H.12 spectroscopic and photophysical properties of series 6, newly synthesized molecules, representing donoracceptor systems were studied. To determine the effect of the structure of the studied compounds on the process of intramolecular electron transfer, modifications of the electron-donor part with unchanged chromophore functioning as an electron acceptor were systematically introduced (compare scheme 1). Moreover, such a selection of compounds made it possible to conduct comparative studies of their photoluminescence properties. The studies were conducted both in a gas phase (measurements of steady-state absorption spectra) as well as in solvents of various polarity using techniques of steady-state and time-resolved spectroscopy. Theoretical quantum-chemical calculations (among others determination of a spatial structure of the compounds studied, electronic energy states, oscillators strength of given transitions, values of factors defining participation of oneelectron transitions between occupied and virtual orbitals in the whole transition and dipole moments) were a supplement of and help with interpretation of the obtained experimental results. Additionally, because of the possibility of rotation around a single bond between the electron donor and acceptor groups, a theoretical conformational analysis of the molecules studied was carried out. Summing up the analysis of the obtained data based on theoretical quantumchemical calculations, it was found that (H.10): In the case of all studied compounds, a long-wavelength absorption band is in fact a superposition of three electron transitions (S 0 S 1, S 0 S 2, S 0 S 3 ). Additionally, changes in density in charge distribution proved that the transition S 0 S 2 possess a charge transfer character. There is a good agreement between absorption spectra (band positions and their intensity) obtained for free molecules, i.e. in the gas phase and theoretically calculated energies of electronic states and their oscillator strengths. A good agreement is also obtained between values of transition dipole moments, theoretically calculated for a molecule being in a gas phase, and experimental, determined by spectroscopic measurements, in non-polar MCH. 23

24 The most favorable energetically conformation in state S 0 state corresponds to the molecular conformation in which the donor and acceptor moieties are orthogonal to each other. Moreover, the studied compounds being in the ground state are represented by a set of conformers of different angle between D and A groups, which combined with dependence of position of maximum lowtemperature fluorescence band (77K) on the excitation wavelength confirms their spectral inhomogeneity (H.12). All the studied compounds in non-polar environments are characterized by a weak coupling between the donor and acceptor parts, which makes it possible to treat them as two independent chromophores ( composite molecular model ), of which mainly the acceptor part is responsible for emission. It is a well-known fact that with a molecule transition from a gas phase to the liquid phase, as well as with the change of solvent, there follows a change in the energy of the excited states. In work H.12 an effect of the environment on the position and character of electron states of 6 studied D-A molecules was analyzed. Time-resolved studies of photophysical processes of the discussed compounds allowed us to state that in the case of molecules in the non-polar environment there are two luminescent centers, having different emission wavelengths and characterized by different decay times. The analysis of fluorescence decay times, as well as time-resolved emission spectra (presence of an isoemissive point) show that apart from emission from an equilibrium, locally excited state there is a possibility of emission from an non-equilibrium state. Moreover, the existence of two-exponential decay times, the presence of isoemissive points in time-resolved emission spectra suggest that to describe correctly the occurring phenomena in the situation where the compounds are in the polar environment, curves of potential energy with a double minimum should be used. It means that the emission follows from the state with intramolecular electron transfer, which is not an equilibrium state (ICT) NR and from a state being in a complete thermally equilibrium (oscillating and configurational) with the environments (ICT) R. 24