Final Scientific Report. October 2011 October 2016

Transcription

1 Final cientific eport ctober 2011 ctober 2016 Title: Luminescent ionic liquid crystals Code: P-II-ID-PCE Project manager: Conferentiar dr. Viorel Cîrcu Liquid crystals based on silver carbene complexes derived from dimeric bis(imidazolium) bromide salts A series of bis(imidazolium) salts with different mesogenic groups (cyanobiphenyl or cholesteryl) and their silver carbene complexes with _ anion has been designed and prepared. The liquid crystalline behaviour of these ionic liquids and their corresponding silver carbene complexes was investigated by polarised optical microscopy (PM), differential scanning calorimetry (DC) and powder -ray diffraction while their thermal stability was studied by thermogravimetric analysis (TGA). The silver complexes are thermally stable on a broad temperature range with accessible transition temperatures close to ambient temperature. The compounds with cholesteryl groups show higher transition temperatures than the compounds possessing cyanobiphenyl mesogenic groups, but their thermal stability is limited by a slight decomposition before reaching the isotropic state. Interestingly, the bis(imidazolium) salt with two cyanobiphenyl groups at each side shows an enantiotropic nematic phase on a short range, being one of the few examples of ILC displaying nematic phase. H ah/thf MeC a-c Ag 2 CH 2 Cl 2 Ag Ag 3a-c C (H 2 C) 10 C C (H 2 C) 5 a b c cheme 1. ynthesis of dimeric bis(imidazolium) salts and their silver carbene complexes. We successfully proved that it is possible to prepare thermally stable silver HC complexes with liquid crystalline properties, with decomposition temperatures significantly higher than their bis(imidazolium) precursors. ursa: C Adv., 2014, 4, 59491, DI: /c4ra11023d Enhancement of smectic C mesophase stability by using branched alkyl chains in the auxiliary ligands of luminescent Pt(II) and Pd(II) complexes A novel series of Pd(II) and Pt(II) complexes based on cyclometallated imine ligands and -benzoylthiourea (BTU) derivatives as auxiliary ligands has been prepared and their liquid crystalline properties as well as photophysical properties have been investigated. The crystal structure of one cyclometallated Pt(II) complex with -(p-f-phenyl)- 0-benzoylthiourea as a co-ligand has been solved. The liquid crystalline properties have been investigated by a combination of DC, PM and variable temperature powder ray diffraction. These new metallomesogens display either a monotropic mc phase or both ma and mc phases, depending on the number of alkoxy groups attached to the imine ligand, alkyl chain length or the use of branched alkoxy terminal groups. We found that the introduction

2 of branched alkoxy terminal groups lead to lower transition temperatures and stabilization of the mc phase in both the Pd(II) and Pt(II) complexes. While the Pd(II) complexes display no emission, the Pt(II) complexes show good emission properties in solution, in the solid state and as a PMMA film at room temperature, and their investigation is reported. C n M 2 BTU K 2 C 3 C n M ' ' C 8 H 17 C 8 H 17 Pt F C n C n = Ac, M = Pd = Cl, M = Pt 1a, b: M = Pd, = H, ' = n-octyl, n = 6, 8 1c: M = Pd, = n-decyl, n = 10 2a,b: M = Pd, = H, ' = 2-ethyl-hexyl, n = 6, 8 2c: M = Pd, = n-decyl, ' = 2-ethyl-hexyl, n = 10 3a,b: M = Pt, = H, ' = 2-ethyl-hexyl, n = 6, 8 3c: M = Pt, = n-decyl, ' = 2-ethyl-hexyl, n = 10 cheme 2. Preparation of Pd(II) and Pt(II) complexes. C 6 H 13 4 ursa: Polyhedron 69 (2014) 31 39, doi : /j.poly Luminescent liquid crystalline materials based on palladium(ii) imine derivatives containing the 2- phenylpyridine core In this work we report our studies concerning the synthesis and characterisation of a series of imine derivatives that incorporate the 2-phenylpyridine (2-ppy) core. These derivatives were used in the cyclometalating reactions of platinum(ii) or palladium(ii) in order to prepare several complexes with liquid crystalline properties. Depending on the starting materials used as well as the solvents employed, different metal complexes were obtained, some of them showing both liquid crystalline behaviour and luminescence properties at room temperature. It was found that, even if there are two competing coordination sites, the cyclometalation process takes place always at the 2-ppy core with (for Pt) or without (for Pd) the imine bond cleavage. We successfully showed that it is possible to prepare emissive room temperature liquid crystalline materials based on double cyclopalladated heteroleptic complexes by varying the volume fraction of the long flexible alkyl tails on the ancillary benzoylthiourea (BTU) ligands. C 8 H 17 H Pd Pd H 1-Pd C 8 H 17 C 12 H 25 C 12 H 25 C 12 H 25 C 12 H 25 a b c C 8 H 17 C 8 H 17 cheme 3. Doubly cyclopaladated luminescent complexes with LC properties. C 12 H 25 ursa: Dalton Trans., 2014, 43, 1151, DI: /c3dt52137k Effect of counterion on the mesomorphic behavior and optical properties of columnar pyridinium ionic liquid crystals derived from 4-hydroxypyridine A series of 3,4,5-tridodecyloxybenzyl pyridinium salts derived from 4-hydroxypyridine has been designed and prepared. The liquid crystalline properties of these compounds were investigated by polarized optical microscopy, differential scanning calorimetry and powder -ray diffraction while their thermal stability was studied by thermogravimetric analysis. The -3,4,5-tridodecyloxybenzyl-4-pyridone intermediate shows a monotropic columnar hexagonal mesophase ranging from 56 o C down to room temperature while the corresponding bromide dodecyl - alkylated pyridinium salt shows one enantiotropic columnar mesophase and one additional monotropic columnar phase at lower temperatures. eplacing bromide ion ( - ) with other counterions ( 3 - ; BF 4 - and PF 6 - ) resulted in mesophase suppression. These luminescent pyridinium salts show weak emission in dichloromethane solutions at room temperature and a pronounced red-shifted emission in solid state. Photoluminescent properties of the pyridinium salts do not depend significantly on the nature of counterion employed.

3 C n C n C n 4-hidroxipiridina ah 2/TBA/THF C n H 2n+ C n C n C n MeC C n C n C n MeC/H 2 C n C n C n - + C n C n (1) (2) (3) (4) - = - (a), 3 - (b), BF 4 - (c), PF 6 - (d) cheme 4. Preparation of ionic liquid crystals derived from 4-hydroxypyridine with various counterions. ursa: J. Mol. truct (2015) , doi: /j.molstruc Columnar bis(pyridinium) ionic liquid crystals derived from 4-hydroxypyridine: synthesis, mesomorphism and emission properties A series of flexibly linked bis(pyridinium) salts with various counterions (, PF 6, BF 4 and Tf - ) was designed and prepared starting from corresponding -alkylated 4-pyridones precursors with mesogenic 3,4,5-tris(alkyloxy)benzyl moieties (alkyl = dodecyl or tetradecyl). These salts were investigated for their liquid crystalline properties by a combination of differential scanning calorimetry, polarising optical microscopy and temperature-dependent powder -ray diffraction (D). Their thermal H TBA/aH THF 1a, b 2a, b C 10 H 20 2 MeH/H 2 MeC - 3a, b stability was checked by thermogravimetric analysis. All bis(pyridinium) salts, except the triflate salt with shorter terminal carbon chain, display an enantiotropic liquid crystalline behaviour with a hexagonal columnar (Colh) phase assigned on the basis of its characteristic texture and D studies. It was found that these luminescent bis(pyridinium) salts show weak emission in dichloromethane solutions at room temperature and a pronounced red-shifted emission in solid state. The emission properties of these bis(pyridinium) salts do not depend significantly on the nature of counterion employed. 4-6a, b ursa: Liquid Crystals, 2016, 43, = PF 6 (4), BF 4 (5), Tf - (6) = C 12 H 25, a C 14 H 29, b Figure 1. Preparation of bis(pyridinium) salts with various counterions A new class of thermotropic lanthanidomesogens: Eu(III) nitrate complexes with mesogenic 4-pyridone ligands A new class of thermotropic lanthanidomesogens has been designed and prepared. They are based on 4-pyridone ligands that possess mesogenic cyanobiphenyl groups attached to the 4-pyridone unit via a flexible long alkyl spacer and show a very high thermal stability (decomposition temperatures near 300 C). Depending on the alkyl length spacer, these complexes exhibit a ma phase with transition temperatures influenced by the number of mesogenic groups employed and the spacer length.

4 ormalised intensity / a.u. Intensity/a.u. ln(i/i o ) H + - 7a-e TBA, ah 8a-e 4-Py Eu( 3 ) 3. 5H 2 EtH 9a-e Eu ( 3 ) 3 (CH 2 ) n (CH 2 ) 9 (CH 2 ) 9 e C n=6, 9, 10 a-c C d C Figure 2. Preparation of Eu(III) complexes with 4-pyridone ligands Emission studies of the Eu(III) complexes with 4-pyridone ligands The emission properties were recorded in solid state and in the liquid crystalline state depending on temperature (Table 1 and Figure 3). Table 1. Emmision lifetimes in solid state Compound /ms a 9a b c d e 0.68 a Estimated error for was ±0.01 ms D 0 7 F 2 3a 3b 3c 3d o C 150 o C F 0 7 F F 3 F /nm /nm /T Figure 3. Emission spectra for Eu(III) complexes 9a-d (left). Temperature dependence of 3b emission by heating from 25 o C to 150 o C (middle). Detection of I-mA transition for 3b: the intensity of 5 D 0 7 F 2 transition versus temperature (right). ursa: Dalton Trans., 2015, 44, 14196, DI: /c5dt01197c. ematic ionic liquid crystals based on pyridinium salts derived from 4-hydroxypyridine A series of pyridinium salts with various counterions (, 3, BF 4, PF 6, Tf and C ) and different spacer chain lengths, which display a nematic phase, have been designed and prepared. They are derived from 4 hydroxypyridine and possess two mesogenic cyanobiphenyl groups attached to the pyridinium unit via a flexible long alkyl spacer (6, 9, 10). These salts exhibit solely a nematic phase with the thermal range influenced by the counterion employed and spacer length.

5 H (CH 2 ) n C TBA/aH THF 1a-c (CH 2 ) n C 2a-c MeC (CH 2 ) n C C (CH 2 ) n (CH 2 ) n C - 3a-c MeH/H 2 C (CH 2 ) n (CH 2 ) n C - - = 3 - (4), BF 4 - (5), PF 6 - (6), Tf - (7), C - (8) n = 6, 9, 10 a-c cheme 5. Preparation of nematic ionic liquid crystals derived from 4-hydroxypyridine. ursa: CrystEngComm, 2016, 18, 5066, DI: /c6ce00618c