Real-Time Observation Of Molecular Flattening And Intersystem Crossing In [(Dpephos)Cu(I)(Pyrtet)] Via Ultrafast Uv/Vis- And Mid-Ir Spectroscopy On Solution And Solid Samples Dagger

The primary photo-induced processes in the mononuclear, heteroleptic Cu(i) complex [(DPEPhos)Cu(PyrTet)] (1), relevant for OLED applications, were investigated in various solvents and in solid state samplesviafemtosecond (fs) time resolved UV/Vis and fs time resolved mid-IR transient absorption spectroscopy (TA) with MLCT excitation around 340 nm. UV/Vis fs-TA on1in solution reveals (i) a severe blue-shift of excited state absorption on the time scale of a few picoseconds (tau(2)) that is not observed in solids, and (ii), on the time scale of several tens of picoseconds (tau(3)), a process with very similar dynamics in all samples. Mid-IR fs-TA in solution indicates structural changes with tau(2). Transient absorption anisotropy experiments temporally resolve a viscosity-dependent change of the excited state transition dipole moment orientation with tau(2), as quantitatively predicted for the relaxed S-1-stateviaTD-DFT. The results strongly suggest flattening distortion (FD) and structural rearrangement of the PyrTet-moiety to occur on the time scale of tau(2)in liquid phase, and to be suppressed in solid phase. Moreover, intersystem crossing (ISC) is assigned to the process described by tau(3), in line with its direct observationviatime-resolved luminescence spectroscopy on1by Bergmannet al.(Sci. Adv., 2016,2, e1500889). Overall, the use of structure-sensitive methods and the direct comparison of different preparations of1(i.e.solutionvs.solid state), are a unique basis for a clear assignment of spectro-temporal characteristics to fundamental deactivation processes such as FD and ISC.