Extension of molecules with an inverted singlet–triplet gap with conjugated branches to alter the oscillator strength

Abstract

{Molecules that violate Hund's Rule and possess negative singlet-triplet gaps (ΔEST) have been actively studied for their potential usage in organic light emitting diodes without the need of thermal activation....

Computational design of boron-free triangular molecules with inverted singlet–triplet energy gap

“…This resurgence of interest in the inversion of S 1 and T 1 excited-state energies was primarily initiated by the computational chemistry community. In recent years, researchers have explored design strategies for the engineering of IST molecules with theoretical and computational methods, 16–20 and the theoretical predictions were confirmed by spectroscopic measurements. 1,3,21,22 Molecular structures discovered by these explorations were predominantly nitrogen-doped phenalenes, such as cyclazine or heptazine derivatives, 1,2 along with related triangular 17,23 or hexagonal polycyclic aromatic hydrocarbons 24 with boron–nitride cores.…”

Resilience of Hund's rule in the chemical space of small organic molecules

“…9 In 2019, two independent studies confirmed STGs o 0 in the prototypical cycl [3.3.3]azines-cyclazine 10 and heptazine 11 -using time-dependent density functional theory (TDDFT) approximations, as well as a few correlated wavefunction methods. Since then, there has been a renewed interest in exploring the historically significant inverse-STG candidates: Ncontaining triangular molecules [12][13][14][15][16][17][18][19][20] and non-alternant hydrocarbons. [21][22][23] Besides these classes of molecules, Bedogni et al 18 showed the possibility of STG o 0 in C n H n N n aza-rings.…”