Toward Circularly Polarized Luminescence from Inherently Chiral Inverted Singlet–Triplet Chromophores

Abstract

Recent years have seen rising interest in molecules that violate Hund’s rule, where the first excited singlet state lies below the triplet (ΔE_ST < 0), accelerating reverse intersystem crossing, a key process in thermally activated delayed fluorescence. We present a computational study on such inverted singlet–triplet (IST) molecules modified for chirality to enable Circularly Polarized Luminescence (CPL), an unexplored direction for IST emitters. Two main chromophores, triangulene and pentalene, were functionalized with minimal chiral groups, preserving negative ΔE_ST, as demonstrated via multiconfigurational calculations. We also explored inherently chiral, nonplanar chromophores, focusing on extended triangulenes resembling helicenes. Substituents enabling enantiomer separation were introduced, and racemization barriers were assessed. When singlet–triplet inversion was lost, structures were further optimized, yielding a promising substrate combining a high racemization barrier, strong CPL, and inverted singlet–triplet energetics, making it suitable for CP-OLED applications.