Supporting information

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1 Supporting information Impact of Donor Substitution Pattern on the TADF Properties in the Carbazolyl-Substituted Triazine Derivatives Tomas Matulaitis, Paulius Imbrasas, Nadzeya A. Kukhta, # Paulius Baronas, Tadas Bučiūnas, Dovydas Banevičius, Karolis Kazlauskas, Juozas V. Gražulevičius,*, and Saulius Juršėnas Department of Polymer Chemistry and Technology, Kaunas University of Technology, Radvilenu pl. 19, LT , Kaunas, Lithuania. Institute of Applied Research, Vilnius University, Sauletekio 9-III, LT Vilnius, Lithuania. # Current address: Department of Chemistry, Durham University, South Road, DH1 3LE, United Kingdom AUTHOR INFORMATION Corresponding Author *prof. Juozas V. Grazulevicius, Department of Polymer Chemistry and Technology, Kaunas University of Technology, Radvilenu pl. 19, LT-50254, Kaunas, Lithuania, Tel. No , juozas.grazulevicius@ktu.lt. S1

2 Contents 1. Instrumentation... S2 2. Thermal and electrochemical properties... S4 3. Theoretical data calculations... S5 4. Photophysical properties... S7 5. References... S8 1. Instrumentation Nuclear magnetic resonance spectra of deuterated chloroform solutions of the synthesized compounds were recorded with a Bruker Avance III 400 spectrometer (400 MHz ( 1 H), 100 MHz ( 13 C)) spectrometer. All the data are given as chemical shifts in δ (ppm), multiplicity, integration down field from (CH 3 ) 4 Si as the internal standard. Mass spectra (MS) were obtained on Schimadzu Biothech Axima mass spectrometer using MALDI-TOF ionization method. Elemental analysis data were obtained on a EuroEA Elemental Analyzer. Infrared (IR) spectra were recorded using Perkin Elmer Spectrum GX II FT IR System. Steady-state measurements. UV Vis spectra of 10-4 M solutions of the compounds were recorded in quartz cells using Perkin Elmer Lambda 35 spectrometer. Photoluminescence (PL) spectra of 10-5 M solutions of the compounds were recorded using Edinburgh Instruments FLS980 Fluorescence Spectrometer. Fluorescence quantum yields (η) of the solutions and of the solid films were estimated using the integrated sphere method 1. An integrating sphere (Edinburgh Instruments) coupled to the FLS980 spectrometer was calibrated with two standards: quinine sulfate in 0.1 M H 2 SO 4 and rhodamine 6G in ethanol. Each quantum yield measurement was repeated 5 times and the error corridor was estimated. Time-resolved measurements. The phosphorescence spectra were recorded at 77 K for the solid solutions of the compounds (1 wt %) in Zeonex polymer matrix using nanosecond gated luminescence measurements (from 400 ps to 1 s) using a high energy pulsed Nd:YAG laser emitting at 355 nm (EKSPLA). A model liquid nitrogen cryostat (Janis Research) was used for the experiment. The blue-edge highest energy peak in the phosphorescence spectrum was taken for the T 1 S 0 transition. Time-resolved luminescence and excitation energy dependence measurements of 1 wt % PMMA films, prepared by drop-casting PMMA and compound mixture in toluene on a glass substrate at room temperature, were performed using a frequency-tripled Nd3+:YAG laser (Ekspla, λ = 355 nm, τ = 25 ps, 10 Hz) as an excitation source and iccd camera New istar DH340T (Andor) as time-gated detector at mbar pressure by exponentially increasing delay and integration time as described in ref 2. The method enabled recording up to 10 orders of magnitude in time and intensity of the fluorescence decay by varying the delay and exposure of the measurement. Temperature- S2

3 dependent time-resolved measurements were performed with a different excitation source, using a nanosecond YAG:Nd3+ laser NT 242 (Ekspla, λ = 350 nm, τ = 7 ns, 100Hz). Samples were measured in temperature controlled closed-cycle helium cryostat. Differential scanning calorimetry (DSC) measurements were carried out with a TA Instruments DSC Q100 calorimeter. The samples were heated at a scan rate of 10 C/min under nitrogen atmosphere. Thermogravimetric analysis (TGA) was performed on a Mettler TGA/SDTA851e/LF/1100. The samples were heated at a rate of 20 C/min. Cyclic voltammetry (CV) measurements were carried out with a glassy carbon working electrode in a three electrode cell using a µ Autolab Type III (EcoChemie, Netherlands) potentiostat. Platinum wire and Ag/AgNO 3 (0.01 mol/l in acetonitrile) were used as counter and reference electrodes, respectively, and Bu 4 NBF 6 in dichloromethane (0.1 M) was used as electrolyte. The data were collected using GPES (General Purpose Electrochemical System) software. Electrochemical measurements were conducted at room temperature at a potential rate of 100 mv/s. The reference electrode was calibrated versus ferrocene/ferrocenium redox couple. The solid state ionization potential energy (I CV p ) was estimated from the onset oxidation potential by using the relationship I CV p = E ox, where the potential is related to that of ferrocenium/ferrocene. The electron affinity (EA CV ) values were obtained from the reduction potential using the approximation EA CV = E red. The theoretical calculations were carried out using the Gaussian 09 quantum chemical package 3. Full geometry optimizations of the compounds in their electronic ground state were performed with density functional theory method (DFT) 4 using the B3LYP functional consisting of Becke s three parameter hybrid exchange functional 5 combined with the Lee-Yang-Parr correlation functional 6 with the 6-31G(d) basis set in vacuum. The spectroscopic properties of the molecules were calculated by the means of time-dependent DFT (TD-DFT) 7 9 calculations employing 6-31G(d) basis set. In the TD-DFT calculations various DFT functionals, containing different percentage of exact Hartree-Fock exchange energy (%HF), were employed. Those were B3LYP (20 %HF), MPW1B95 (31 %HF) 10, along with the long range corrected functional ωb97x-d 11. In order to properly analyze the nature of the excited states, the natural transition orbital (NTO) 12 analysis was performed, with NTOs calculated at the chosen functional for every tested molecule/6-31g(d) level in gas phase. Graphical visualizations of theoretical absorption spectra were accessed with the help of GaussSum software 13. Multiwfn software 14 was used to evaluate molecular fragment contribution to occupied and virtual orbits. OLED characterization. The pre-cleaned 22x22 mm ITO-coated glass substrates were treated with O2 plasma for 5 min. The substrates then were put into inert gas atmosphere and subsequently into a high vacuum (8 10 Pa) chamber. Organic layers were deposited by thermal evaporation onto the substrates with evaporation rates of nm/s. Next, a cathode was fabricated by thermally evaporating LiF (0.8 nm) and Al (100 nm) S3

4 with rates of 0.01 nm/s and nm/s, respectively. The pixel size of each OLED was 1 mm2 with a total of 6 pixels per substrate. After evaporation, the OLEDs were encapsulated with a clear glass cover to prevent the detrimental effects of O2 and H2O. The voltage, current and luminance characteristics of the OLEDs were measured in ambient air atmosphere with a Keithley 2601A Source Meter, Orb Optronics ETO TEC 100 characterization system and RadOMA GS-1290 spectroradiometer. 2. Thermal and electrochemical properties Weight (%) T ID =447 o C Temperature ( o C) Heat flow 1 st heating cooling 2 nd heating T G = 222 o C T M = 388 o C Temperature, o C Figure S1. (a) TGA and (b) DSC curves of Current (A) 8,0x10-5 4,0x10-5 0,0-4,0x ,5-2,0-1,5 0,0 0,5 1,0 1,5 Potential (V vs Ag/Ag + ) Energy, ev 7,0 6,5 6,0 5,5 5,0 4,5 4,0 3,5 3,0 2,5 2, ev 2.83 ev 5.65 ev IP CV EA CV 2.78 ev Figure S2. Cyclic voltammetry scans and energy levels of and. S4

5 3. Theoretical data calculations Figure S3. B3LYP/6-31G(d) optimized geometries of and. Triazine moiety is encircled; for convenience hydrogens are omitted. OHF method The detailed procedure of method is described in literature 15. The amount of charge, transferred from donor to acceptor (q) is analyzed using Multiwfn software 14 based on the B3LYP optimized S 0 geometry and calculated using formulas: (1) a i b i > 0, (2) a i b i < 0, (3) OHF = 42 q, Where 1, 1 and q = q + = q -. The index i denotes the number of fragments (atoms, phenyl groups, or carbazole groups); a i and b i are the contribution percentages of different molecular fragments in the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO), respectively. Since it was shown that q, calculated from the weighted averages of each transition is close to that calculated from HOMO LUMO transition 15, for convenience, the CT amount in HOMO LUMO transition is used to approximate that in S 1 transition. Finally, optimal HF% is calculated using relation (3). S5

6 Table S1. Analysis of selected electronic transitions of and. Transition Wavelength Osc. (nm) Strength Major contributions HOMO-1 > LUMO (13%), HOMO-1 > LUMO+1 (19%), HOMO > LUMO (54%) HOMO-1 > LUMO (45%), HOMO-1 > LUMO+1 (18%), HOMO > LUMO (26%), HOMO > LUMO+1 (10%) HOMO-2 > LUMO+1 (87%) HOMO-2 > LUMO (21%), HOMO-1 > LUMO+1 (19%), HOMO > LUMO+1 (42%) HOMO-2 > LUMO+1 (22%), HOMO-1 > LUMO (24%), HOMO > LUMO (37%), HOMO > LUMO+1 (10%) Minor contributions HOMO-2 > LUMO+1 (8%), HOMO > LUMO+1 (3%) HOMO-2 > LUMO (2%), HOMO-1 > LUMO (2%), HOMO > LUMO (5%) HOMO-1 > LUMO (2%), HOMO-1 > L+2 (2%), HOMO > LUMO (9%) HOMO-2 > LUMO+2 (2%) Figure S4. Frontier orbitals (MPW1B G in vacuum) of and. S6

7 Normalized UV intensity (a.u.) 1,0 0,5 0, ,0 0,5 Zeonex B3LYP Zeonex ωb97x-d 0,06 Zeonex B3LYP S 0-1 S 0-1 0, ,2 Zeonex ωb97x-d S 0-1 0,04 0,02 0,8 0,4 Oscillator strength S 0-1 0, Wavelength (nm) Wavelength (nm) 0,0 Figure S5. Theoretical (TD-DFT rb3lyp and ωb97x-d 6-31G/vacuum, blue columns) excitations and experimental (Zeonex, green curves) absorption spectra of and. 4. Photophysical properties PL UV Normalized PL intensity (a.u.) 1 0,1 0,01 1 PL λ 0,1 HEX TOL THF o-dcb 0,01 1,8 2,0 2,2 2,4 2,6 2,8 3,0 3,2 3,4 3,6 3,8 4,0 4,2 4,4 Energy (ev) UV HEX TOL THF o-dcb 1 0,1 0,01 1 0,1 0,01 Normalized UV intensity (a.u.) Figure S6. UV/Vis absorption and photoluminescence spectra in various solvents of and. Dashed line depicts absorption edge of. S7

8 Table S2. Summary of various optical parameters of and. Solvent λ UV, ev λ PL, ev Stokes Stokes Solvent λ shift, ev UV, ev λ PL, ev shift, ev Hexane Hexane Toluene Toluene THF THF o-dcb o-dcb References (1) de Mello, J. C.; Wittmann, H. F.; Friend, R. H. An Improved Experimental Determination of External Photoluminescence Quantum Efficiency. Adv. Mater. 1997, 9 (3), (2) Rothe, C.; Monkman, A. P. Triplet Exciton Migration in a Conjugated Polyfluorene. Phys. Rev. B 2003, 68 (7), (3) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; et al. Gaussian 09, Revision A.02. Gaussian 09, Revision A (4) Calais, J.-L. Density-Functional Theory of Atoms and Molecules. R.G. Parr and W. Yang, Oxford University Press, New York, Oxford, Int. J. Quantum Chem. 1993, 47 (1), (5) Becke, A. D. Density-Functional Thermochemistry. III. The Role of Exact Exchange. J. Chem. Phys. 1993, 98 (7), (6) Lee, C.; Yang, W.; Parr, R. G. Development of the Colle-Salvetti Correlation-Energy Formula into a Functional of the Electron Density. Phys. Rev. B 1988, 37 (2), (7) Gross, E. K. U.; Kohn, W. Local Density-Functional Theory of Frequency-Dependent Linear Response. Phys. Rev. Lett. 1986, 57 (7), (8) Bauernschmitt, R.; Ahlrichs, R. Treatment of Electronic Excitations within the Adiabatic Approximation of Time Dependent Density Functional Theory. Chem. Phys. Lett. 1996, 256 (4 5), (9) Thanthiriwatte, K. S.; Gwaltney, S. R. Excitation Spectra of Dibenzoborole Containing π-electron Systems: Controlling the Electronic Spectra by Changing the P π π* Conjugation. J. Phys. Chem. A 2006, 110 (7), (10) Zhao, Y.; Truhlar, D. G. Hybrid Meta Density Functional Theory Methods for Thermochemistry, Thermochemical Kinetics, and Noncovalent Interactions: The MPW1B95 and MPWB1K Models and S8

9 Comparative Assessments for Hydrogen Bonding and van Der Waals Interactions. J. Phys. Chem. A 2004, 108 (33), (11) Chai, J.-D.; Head-Gordon, M. Long-Range Corrected Hybrid Density Functionals with Damped Atom atom Dispersion Corrections. Phys. Chem. Chem. Phys. 2008, 10 (44), (12) Martin, R. L. Natural Transition Orbitals. J. Chem. Phys. 2003, 118 (11), (13) O Boyle, N. M.; Tenderholt, A. L.; Langner, K. M. Cclib: A Library for Package-Independent Computational Chemistry Algorithms. J. Comput. Chem. 2008, 29 (5), (14) Lu, T.; Chen, F. Multiwfn: A Multifunctional Wavefunction Analyzer. J. Comput. Chem. 2012, 33 (5), (15) Huang, S.; Zhang, Q.; Shiota, Y.; Nakagawa, T.; Kuwabara, K.; Yoshizawa, K.; Adachi, C. Computational Prediction for Singlet- and Triplet-Transition Energies of Charge-Transfer Compounds. J. Chem. Theory Comput. 2013, 9 (9), S9