A 9,9′-bianthracene-cored molecule enjoying twisted intramolecular charge transfer to enhance radiative-excitons generation for highly efficient deep-blue OLEDs

The efficiency of fluorescent organic light emitting diodes (FOLEDs) is strongly affected by the fraction of singlet excitons formed. However, the standard statistical value of the single to triplet ratio is 1:3, which implies most of the excitons are invalid in fluorescent emitting devices. Here, we demonstrate the ability of twisted intramolecular charge transfer state (TICT-state) to enhance the occurrence of singlet excitons in a fluorescent emitter that is based on the 9,9′-bianthracene (BA) moiety. The anthracene–anthracene (A–A) linked by a single bond and having perpendicular electronic structure is a charge transfer intersystem crossing π system in excited state. The BA-cored fluorescence emitter (CzBACz) with particular TICT characteristics realizes the electron–hole (e–h) recombination via intramolecular conversion from charge-transfer excitons (immediate precursor) to radiative singlet exciton (final state). For CzBACz-based electroluminescent (EL) device, the singlet generation fraction is more than 25%.

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► The PL of the BA-cored emitter (CzBACz) shows dual fluorescence in solution.
► The dual fluorescence arises from LE-state and CT-state.
► CzBACz-based devices show deep-blue emission and relative good EL performances.
► CT excitons generating newborn local excitons (LEs) should be a pathway for high efficiency EL.