Carbene-Metal-Amide Bond Deformation, Rather Than Ligand Rotation, Drives Delayed Fluorescence

Elliot J. Taffet, Yoann Olivier, Frankie Lam, David Beljonne, Gregory D. Scholes

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We report three characteristics of ideal thermally activated delayed fluorescence molecular systems apparent in carbene-metal-amides: (a) an exceptionally small singlet-triplet gap that effectively eliminates the thermal activation barrier to reverse intersystem crossing; (b) significant singlet oscillator strength promoting fluorescence in the region of this small barrier; and (c) enlarged spin-orbit coupling driving reverse intersystem crossing in this region. We carry out highly correlated quantum-chemical calculations to detail the relative energies of and spin-orbit couplings between the singlet and triplet states, finding that they fall closer together in energy and couple more strongly in going from the singlet ground-state to the triplet optimized geometry. This structural reorganization is defined not by rotation of the ligands but by a nontrivial bending of the carbene-metal-amide bond angle. This bending reduces carbene-metal-amide symmetry and enhances singlet-triplet interaction strength. We clarify that the reverse intersystem crossing triggering delayed fluorescence occurs around the coplanar triplet geometric optimum.

langue originaleAnglais
Pages (de - à)1620-1626
Nombre de pages7
journalJournal of Physical Chemistry Letters
Numéro de publication7
Les DOIs
Etat de la publicationPublié - 5 avr. 2018
Modification externeOui

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