Fluorescence via Reverse Intersystem Crossing from Higher Triplet States in a Bisanthracene Derivative

Abstract

To elucidate the high external quantum efficiency observed for organic light-emitting diodes using a bisanthracene derivative (BD1), non-radiative transition processes as well as radiative ones are discussed employing time-dependent density functional theory. It has been previously reported that the observed high external quantum efficiency of BD1 cannot be explained by the conventional thermally activated delayed fluorescence involving T1 exciton nor triplet-triplet annihilation. The calculated off-diagonal vibronic coupling constants of BD1, which govern the non-radiative transition rates, suggest a fluorescence via higher triplets (FvHT) mechanism, which entails the conversion of a high triplet exciton generated during electrical excitation into a fluorescent singlet exciton. This mechanism is valid as long as the relaxation of high triplet states to lower states is suppressed. In the case of BD1, its pseudo-degenerate electronic structure helps the suppression. A general condition is also discussed for the suppression of transitions in molecules with pseudo-degenerate electronic structures.

Solvent-dependent investigation of carbazole benzonitrile derivatives: does the LE3−CT1 energy gap facilitate thermally activated delayed fluorescence?

“…[11][12][13][14] In addition to these exciting applications of TADF, the fundamental processes in TADF are also attracting considerable interest in both experimental and theoretical fields. [15][16][17][18][19][20][21][22][23][24][25][26] In this case, the goal is to achieve a sufficient understanding of these processes to realize a high RISC rate (k RISC ) by judicious designing and optimizing the most suitable chemical structures, emission environments, and so on. Increasing the k RISC suppresses triplet state quenching and is, therefore, beneficial for reducing roll-off in OLEDs and organic laser diodes.…”

The Photophysics of Dibenzo[a,j]phenazine

“…An alternative to TADF for efficient OLED emission makes use of higher triplet states and their reverse intersystem crossing (HIGHrISC). [12][13][14] HIGHrISC was shown to occur in aromatic carbonyls. [15] In these carbonyls, fast rISC starting from a higher triplet state of nπ* character may occur.…”

“…An alternative to TADF for efficient OLED emission makes use of higher triplet states and their reverse intersystem crossing (HIGHrISC) [12–14] . HIGHrISC was shown to occur in aromatic carbonyls [15] .…”

Origin of aggregation-induced enhanced emission: role of pseudo-degenerate electronic states of excimers formed in aggregation phases

“…Sato et al have already reported that, in fluorescent dopants employed in organic lightemitting diodes (OLEDs), radiative and non-radiative transitions from a triplet excited state T n (n > 1) to all the lower triplet excited states can be suppressed due to the pseudodegenerate electronic states. [18][19][20] The pseudo-degeneracy leads to cancellation of the overlap density between the excited states, which generates T n excitons with long lifetimes. This enables the fluorescence via higher triplets (FvHT) mechanism for OLEDs, that is fluorescence utilizing the reverse intersystem crossing (RISC) from T n to singlets.…”

“…21,22 The FvHT mechanism is proposed to explain the mechanism of electroluminescence in some OLED dopants with large ∆E S 1 −T 1 , where T 1 excitons cannot overcome the energy difference thermally. 19,23 A cyano-substituted 1,2-bis(pyridylphenyl)ethene (CNPPE) ( Fig. 1) has been reported to exhibit the AIEE behavior in solid phase.…”