biostudies-literatureUnknown14(14)Blasco DDelayed fluorescence from molecules with an inverted singlet-triplet gap (DFIST) is the consequence of the unusual reverse order of the lowest excited singlet (S₁) and triplet (T₁) states of thermally activated delayed fluorescence (TADF) emitters. Heptazine (1,3,4,6,7,9,9<i>b</i>-heptaazaphenalene) derivatives have an inverted singlet-triplet gap thanks to the combination of multiple resonance (MR) effects and a significant double excitation character. Here, we study computationally the effect of gold(i) metalation and coordination on the optical properties of heptazine (molecule 4) and the phosphine-functionalized 2,5,8-tris(dimethylphosphino)heptazine derivatives (molecules 1-3). <i>Ab initio</i> calculations at the approximate second-order coupled cluster (CC2) and extended multiconfigurational quasi degenerate perturbation theory at the second order (XMC-QDPT2) levels show that molecules 1-4 have an inverted singlet-triplet gap due to the alternating spatial localization of the electron and hole of the exciton in the heptazine core. A non-vanishing one-electron spin-orbit coupling operator matrix element between T₁ and and a fast S₁ ← T₁ intersystem crossing rate constant (<i>k</i> _ISC) calculated at the XMC-QDPT2(12,12) level of theory for molecule 4 suggest that this new family of complexes may be the first organometallic DFIST emitters reported.Chemical science3873-3880https://www.ebi.ac.uk/biostudies/studies/S-EPMC10074427biostudies-literatureGold(i)-containing light-emitting molecules with an inverted singlet-triplet gap.PMC10074427Valiev RRNasibullin RTSundholm DBlasco DfalseGold(i)-containing light-emitting molecules with an inverted singlet-triplet gap.Delayed fluorescence from molecules with an inverted singlet-triplet gap (DFIST) is the consequence of the unusual reverse order of the lowest excited singlet (S₁) and triplet (T₁) states of thermally activated delayed fluorescence (TADF) emitters. Heptazine (1,3,4,6,7,9,9<i>b</i>-heptaazaphenalene) derivatives have an inverted singlet-triplet gap thanks to the combination of multiple resonance (MR) effects and a significant double excitation character. Here, we study computationally the effect of gold(i) metalation and coordination on the optical properties of heptazine (molecule 4) and the phosphine-functionalized 2,5,8-tris(dimethylphosphino)heptazine derivatives (molecules 1-3). <i>Ab initio</i> calculations at the approximate second-order coupled cluster (CC2) and extended multiconfigurational quasi degenerate perturbation theory at the second order (XMC-QDPT2) levels show that molecules 1-4 have an inverted singlet-triplet gap due to the alternating spatial localization of the electron and hole of the exciton in the heptazine core. A non-vanishing one-electron spin-orbit coupling operator matrix element between T₁ and and a fast S₁ ← T₁ intersystem crossing rate constant (<i>k</i> _ISC) calculated at the XMC-QDPT2(12,12) level of theory for molecule 4 suggest that this new family of complexes may be the first organometallic DFIST emitters reported.2023-01-01T00:00:00Z2023 Apr2025-04-19T17:28:18.288Z2025-04-19T17:28:18.288ZS-EPMC100744273703570010.1039/d3sc00345k