The role of excited-state character, structural relaxation, and symmetry breaking in enabling delayed fluorescence activity in push-pull chromophores

Patrick Kimber, Pooja Goddard, Iain A. Wright, Felix Plasser*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

Thermally activated delayed fluorescence (TADF) is a current promising route for generating highly efficient light-emitting devices. However, the design process of new chromophores is hampered by the complicated underlying photophysics. In this work, four closely related donor-π-Acceptor-π-donor systems are investigated, two of which were synthesised previously, with the aim of elucidating their varying effectiveness for TADF. We outline that the frontier orbitals are insufficient for discriminating between the molecules. Subsequently, a detailed analysis of the excited states at a correlated ab initio level highlights the presence of a number of closely spaced singlet and triplet states of varying character. Results from five density functionals are compared against this reference revealing dramatic changes in, both, excited state energies and wavefunctions following variations in the amount of Hartree-Fock exchange included. Excited-state minima are optimised in solution showing the crucial role of structural variations and symmetry breaking for producing a strongly emissive S1 state. The adiabatic singlet-Triplet gaps thus obtained depend strongly on the range separation parameter used in the hybrid density functional calculations. More generally, this work highlights intricate differences present between singlet and triplet excited state wavefunctions and the challenges in describing them accurately.

Original languageEnglish
Pages (from-to)26135-26150
Number of pages16
JournalPhysical Chemistry Chemical Physics
Volume23
Issue number46
Early online date8 Nov 2021
DOIs
Publication statusE-pub ahead of print - 8 Nov 2021

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