Abstract
We introduce a simple quantum-mechanical model for thermally activated
delayed fluorescence (TADF). The Hamiltonian is represented in the basis
of four spin-mixed diabatic states representing pure charge transfer
(CT) and local excitations (LE). The model predicts that it is possible
to realize lowest-lying adiabatic singlet (S1) and triplet (T1) states with a small singlet–triplet gap, differing CT/LE contributions, and appreciable LE component in the S1 state. These characteristics can explain the coexistence of fast T1 → S1 reverse intersystem crossing and S1 → S0
radiative decay in some chromophores. Through the sampling of the
parameter space and statistical analysis of the data, we show which
parameter combinations contribute the most to the TADF efficiency. We
also show that conformational fluctuations of a single model
donor–acceptor system sample a significant region of the parameter space
and can enhance the TADF rate by almost 3 orders of magnitude. This
study provides new guidelines for optimization of TADF emitters by means
of electronic structure and conformation engineering.
Original language | English |
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Journal | Chemistry of Materials |
Volume | 31 |
Issue number | 17 |
Pages (from-to) | 6995-7006 |
ISSN | 0897-4756 |
DOIs | |
Publication status | Published - 2019 |