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. Issue 25 (17th June 2020)

• Record Type: Journal Article
• Authors: Grupe, Merten; Bäppler, Florian; Theiß, Maximilian; Busch, Jasmin M.; Dietrich, Fabian; Volz, Daniel; Gerhards, Markus; Bräse, Stefan; Diller, Rolf
• Is Part Of: Physical chemistry chemical physics. Volume 22:Issue 25(2020)
• Page Start: 14187
• Page End: 14200
• Publication Date: 2020-06-17
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/c9cp05749h
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : Spotlight on a photoexcited heteroleptic Cu(i ) complex: elucidation of ultrafast electronic and structural dynamics. Abstract : 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 samples via femtosecond (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 on 1 in solution reveals (i) a severe blue-shift of excited state absorption on the time scale of a few picoseconds ( τ 2 ) that is not observed in solids, and (ii), on the time scale of several tens of picoseconds ( τ 3 ), a process with very similar dynamics in all samples. Mid-IR fs-TA in solution indicates structural changes with τ 2 . Transient absorption anisotropy experiments temporally resolve a viscosity-dependent change of the excited state transition dipole moment orientation with τ 2, as quantitatively predicted for the relaxed S1 -state via TD-DFT. The results strongly suggest flattening distortion (FD) and structural rearrangement of the PyrTet-moiety to occur on the time scale of τ 2 in liquid phase, and to be suppressed in solid phase. Moreover, intersystem crossing (ISC) is assigned to the process described by τ 3, in line with its direct observation via time-resolved luminescence spectroscopy on 1 by Bergmann et al. ( Sci. Adv., 2016, 2, e1500889). Overall, the use of structure-sensitive methods and the direct comparison of different preparations of 1 ( i.e. solution vs. solid state), are a unique basis for a clear assignment of spectro-temporal characteristics to fundamental deactivation processes such as FD and ISC.