Vibrationally Assisted Intersystem Crossing in Benchmark Thermally Activated Delayed Fluorescence Molecules

Emrys W. Evans, Yoann Olivier, Yuttapoom Puttisong, William K. Myers, Timothy J.H. Hele, S. Matthew Menke, Tudor H. Thomas, Dan Credgington, David Beljonne, Richard H. Friend, Neil C. Greenham

Research output: Contribution to journalArticlepeer-review

Abstract

Electrically injected charge carriers in organic light-emitting devices (OLEDs) undergo recombination events to form singlet and triplet states in a 1:3 ratio, representing a fundamental hurdle for achieving high quantum efficiency. Dopants based on thermally activated delayed fluorescence (TADF) have emerged as promising candidates for addressing the spin statistics issue in OLEDs. In these materials, reverse singlet-triplet intersystem crossing (rISC) becomes efficient, thereby activating luminescence pathways for weakly emissive triplet states. However, despite a growing consensus that torsional vibrations facilitate spin-orbit-coupling- (SOC-) driven ISC in these molecules, there is a shortage of experimental evidence. We use transient electron spin resonance and theory to show unambiguously that SOC interactions drive spin conversion and that ISC is a dynamic process gated by conformational fluctuations for benchmark carbazolyl-dicyanobenzene TADF emitters.

Original languageEnglish
Pages (from-to)4053-4058
Number of pages6
JournalJournal of Physical Chemistry Letters
Volume9
Issue number14
DOIs
Publication statusPublished - 19 Jul 2018
Externally publishedYes

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