The discovery of triangular-shaped molecules displaying an inverted singlet–triplet (INVEST) energy gap between their lowest singlet (S1) and triplet (T1) 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 ΔEST 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 S1 and T1, 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 S1.
Enhancing Reverse Intersystem Crossing with Extended Inverted Singlet–Triplet (X−INVEST) Systems
Landi, Alessandro;
2024-01-01
Abstract
The discovery of triangular-shaped molecules displaying an inverted singlet–triplet (INVEST) energy gap between their lowest singlet (S1) and triplet (T1) 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 ΔEST 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 S1 and T1, 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 S1.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.