Theoretical rationalization of the singlet-triplet gap in oleds materials: Impact of charge-transfer character

M. Moral, L. Muccioli, W. J. Son, Y. Olivier, J. C. Sancho-Garcia

Research output: Contribution to journalArticle

Abstract

New materials for OLED applications with low singlet-triplet energy splitting have been recently synthesized in order to allow for the conversion of triplet into singlet excitons (emitting light) via a Thermally Activated Delayed Fluorescence (TADF) process, which involves excited-states with a non-negligible amount of Charge-Transfer (CT). The accurate modeling of these states with Time-Dependent Density Functional Theory (TD-DFT), the most used method so far because of the favorable trade-off between accuracy and computational cost, is however particularly challenging. We carefully address this issue here by considering materials with small (high) singlet-triplet gap acting as emitter (host) in OLEDs and by comparing the accuracy of TD-DFT and the corresponding Tamm-Dancoff Approximation (TDA), which is found to greatly reduce error bars with respect to experiments thanks to better estimates for the lowest singlet-triplet transition. Finally, we quantitatively correlate the singlet-triplet splitting values with the extent of CT, using for it a simple metric extracted from calculations with double-hybrid functionals, that might be applied in further molecular engineering studies.

Original languageEnglish
Pages (from-to)168-177
Number of pages10
JournalJournal of Chemical Theory and Computation
Volume11
Issue number1
DOIs
Publication statusPublished - 13 Jan 2015
Externally publishedYes

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