Speaker
Description
Computational description of light emission processes in organic TADF blue emitters
Georgia Ivanova, Simona Djumayska, Neda Todorova, Anela Ivanova
Faculty of Chemistry and Pharmacy, Sofia University, 1 James Bourchier blvd., Sofia, Bulgaria
E-mail: aivanova@chem.uni-sofia.bg
Organic light emitting diodes (OLEDs) are among the optoelectronic devices for which research is employed intensively to enhance their performance [1]. Blue OLEDs suffer from relatively short lifetimes and comparatively low lighting efficiency. One of the approaches to improve their characteristics is the development of luminophores with potential for thermally activated delayed fluorescence (TADF). These are compounds with high-energy excited triplet states and closely separated excited singlets. Therein, reverse intersystem crossing via thermal fluctuations might increase the overall luminescence quantum yield. In the current study, computational design is applied to estimate the characteristics of the light emission processes in a series of new organic compounds, which may emit blue light and have feasible TADF.
The structure and optical properties of a set of donor-spacer-acceptor molecules are computed with (TD)DFT [2]. The geometry of the ground and all relevant excited states is optimized. Energy and oscillator strength of the fluorescence and energy separation of the singlet and triplet excited states are used to assess the capacity for blue TADF-assisted emission. The rate constants of the various excited state deactivation processes are evaluated. The relative importance of several molecular factors for accomplishing the desired luminescence characteristics is tracked. Meta-binding to the spacer is found essential for a high-energy triplet excited state. To ensure non-zero oscillator strength of the fluorescence transition, the donor and the acceptor should close an angle lower than 75o in S1 and their frontier orbitals should overlap partially on the spacer. The pi-conjugation length of the chromophore should not exceed three rings for blue fluorescence to take place.
Following the derived molecular guidelines, several compounds are put forward as promising blue emitters for organic light-emitting diodes. Characteristic times for delayed fluorescence in the microsecond to millisecond time range are predicted for them.
The research is funded by the Bulgarian National Scientific Fund, Project № KP-06-N49/3 from 26. 11. 2020.
References
[1] Th.-T. Bui, F. Goubard, M. Ibrahim-Ouali, D. Gigmes, Fr. Dumur, Beilstein J. Org. Chem., 2018, 14, 282-308.
[2] G. Ivanova, N. Bozova, N. Petkov, C. An, B. Hu, M. Mutovska, K. Konstantinov, Y. Zagranyarski, V. Videva, A. Yordanova, M. Baumgarten, A. Ivanova, Chem Eur. J., 2022, e202104411.
