The discovery of singlet–triplet
(ST) inversion
in some
π-conjugated triangle-shaped boron carbon nitrides is a remarkable
breakthrough that defies Hund’s first rule. Deeply rooted in
strong electron–electron interactions, ST inversion has garnered
significant interest due to its potential to revolutionize triplet
harvesting in organic LEDs. Using the well-established Pariser–Parr–Pople
model for correlated electrons in π-conjugated systems, we employ
a combination of CISDT and restricted active space configuration interaction
calculations to investigate the photophysics of several triangular
boron carbon nitrides. Our findings reveal that ST inversion in these
systems is primarily driven by a network of alternating electron-donor
and electron-acceptor groups in the molecular rim, rather than by
the triangular molecular structure itself.