Thermally activated delayed fluorescence processes for Cu(I) complexes in solid-state: a computational study using quantitative prediction

The photophysical properties of four representative Cu(i) complex crystals have been investigated using the combination of an optimally tuned one- and two-dimensional range-separated hybrid functional (LC-BLYP alpha=0.0,beta=1.0* and LC-BLYP alpha=0.2,beta=0.8**) with the polarizable continuum model, and the thermal a= , vibration correlation function (TVCF) approach. The calculated excited singlet-triplet energy gap, radiative rates and lifetimes match the experimentally available data perfectly. At 300 K, the reverse intersystem crossing (RISC) proceeds at a rate of k(RISC)(dir.) approximate to 10(6-8) s(-1), s which is 4-5 orders of magnitude larger than the mean phosphorescence rate, k(P) approximate to 10(2-3) s(-1). At the same time, the ISC rate k(ISC)(dir.) approximate to 10(9) s(-1) is again 2 orders of magnitude larger than the fluorescence rate k(F) approximate to 10(7) s(-1). In the case of k(RISC)(dir.) >> k(F) and k(RISC)(dir.) >> k(P), thermally activated delayed fluorescence should occur. Vibronic spin-orbit coupling can remarkably enhance the ISC rates by the vital "promoting" modes, which can provide crucial pathways to decay. This can be helpful for designing novel excellent TADF Cu(I) complex materials.