Enhancing Reverse Intersystem Crossing with Extended Inverted Singlet–Triplet (X−INVEST) Systems
Gaetano Ricci, Alessandro Landi, J. C. Sancho-Garcı́a, Yoann Olivier
Abstract
Abstract The discovery of triangular‐shaped molecules displaying an inverted singlet–triplet (INVEST) energy gap between their lowest singlet (S 1 ) and triplet (T 1 ) states opened the way for a new strategy to increase the internal quantum efficiency (IQE) of organic light‐emitting diodes (OLEDs), enhancing the reverse intersystem crossing (RISC) thanks to a downhill process. However, the compounds showing a negative ΔE ST suffer from both a vanishing spin–orbit coupling (SOC) between these excited states and high energy differences with higher‐lying singlets and triplets, therefore limiting their involvement in the spin conversion process. Here, we proposed a new design strategy entailing the extension of the triangulene cores by connecting two INVEST triangulene units to form Uthrene‐ and Zethrene‐like systems, doped with N and B. The inspection of the resulting molecular orbitals (MOs) distribution allowed rationalizing the electronic structure properties obtained from wavefunction‐based methods, showing how the Uthrene‐like architecture can lead to the quasi ‐resonance between S 1 and T 1 , in some cases provoking their inversion. By feeding a kinetic model with the non‐radiative rate constants, calculated from first principles, we showed how the extended INVEST (X−INVEST) design strategy can open new pathways to boost the spin conversion process and the population of the emissive S 1 .