Luminescent Dinuclear Copper(I) Complexes as Potential Thermally Activated Delayed Fluorescence (TADF) Emitters: A Theoretical Study

The
excited state properties of a series of binuclear NHetPHOS–Cu­(I)
complexes (NHetPHOS) have been investigated by means of density functional
theory (DFT) and time-dependent DFT (TD-DFT). It is shown that experimental
trends observed in powder, generally explored via S1 and
T1 excited state energetics and S1 ⇔
T1 intersystem crossing (ISC) efficiency, are hardly analyzed
on the basis of excited state properties calculated in solution. Indeed,
several local minima corresponding to various structural deformations
are evident on the lowest excited state potential energy surfaces
(PES) when solvent correction is applied, leading to a four-state
thermally activated delayed fluorescence (TADF) mechanism. In contrast,
preliminary simulations performed in the solid point to the reduction
of nuclear flexibility and consequently to a rather simple two-state
model.