In the last years, an increasing number of fully organic molecules capable of thermally activated delayed fluorescence (TADF) have been reported, often with very small or even inverted singlettriplet (INVEST) energy gaps.1 These molecules typically exhibit complex photophysics, due to the close energy However, all the molecular systems showing a negative ΔEST suffer from both a vanishing Spin-Orbit Coupling between the lowest singlet (S1) and triplet (T1) excited states and high energy differences with higher-lying singlet and triplet excited states, precluding their involvement in the spin conversion process.2 In our works3 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 atoms. A detailed inspection of the resulting molecular orbital distribution allowed rationalizing the electronic structure properties obtained employing wavefunction-based methods (NEVPT2, EOM-CCSD, SCS-CC2), showing how the Uthrene-like architecture can give origin to the energy proximity between the lowest singlet and triplet excited states, in some cases leading to their energy inversion. By feeding a kinetic model with the non-radiative rate constants calculated from first principle 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 excited state.
Enhancing Reverse Intersystem Crossing with Extended Inverted Singlet-Triplet (X−INVEST) systems
Alessandro Landi
;
2025
Abstract
In the last years, an increasing number of fully organic molecules capable of thermally activated delayed fluorescence (TADF) have been reported, often with very small or even inverted singlettriplet (INVEST) energy gaps.1 These molecules typically exhibit complex photophysics, due to the close energy However, all the molecular systems showing a negative ΔEST suffer from both a vanishing Spin-Orbit Coupling between the lowest singlet (S1) and triplet (T1) excited states and high energy differences with higher-lying singlet and triplet excited states, precluding their involvement in the spin conversion process.2 In our works3 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 atoms. A detailed inspection of the resulting molecular orbital distribution allowed rationalizing the electronic structure properties obtained employing wavefunction-based methods (NEVPT2, EOM-CCSD, SCS-CC2), showing how the Uthrene-like architecture can give origin to the energy proximity between the lowest singlet and triplet excited states, in some cases leading to their energy inversion. By feeding a kinetic model with the non-radiative rate constants calculated from first principle 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 excited state.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
