Excitation-Wavelength-Dependent Photophysics of d8 d8 Di-isocyanide Complexes


Pizl M, Hunter BM, Sazanovich IV, Towrie M, Gray HB, Zalis S, Vlcek A. Excitation-Wavelength-Dependent Photophysics of d8 d8 Di-isocyanide Complexes [Internet]. ACS Inorganic Chemitry 2021;


Binuclear Rh(I) and Ir(I) TMB (2,5-dimethyl-2,5-diisocyanohexane) and dimen (1,8-diisocyanomenthane) complexes possess dσ*pσ and dπpσ singlet and triplet excited states that can be selectively excited in the visible and UV spectral regions. Using perturbational spin–orbit TDDFT, we unraveled the detailed character and spin mixing of these electronic transitions and found that delocalization of pσ and dπ orbitals over C≡N– groups makes C≡N stretching vibrations sensitive reporters of electron density and structural changes upon electronic excitation. Picosecond time-resolved infrared spectra measured after visible light, 375 nm, and 316 nm excitation revealed excitation-wavelength-dependent deactivation cascades. Visible light irradiation prepares the 1dσ*pσ state that, after one or two (sub)picosecond relaxation steps, undergoes 70–1300 ps intersystem crossing to 3dσ*pσ, which is faster for the more flexible dimen complexes. UV-excited 1,3dπpσ states decay with (sub)picosecond kinetics through a manifold of high-lying triplet and mixed-spin states to 3dσ*pσ with lifetimes in the range of 6–19 ps (316 nm) and 19–43 ps (375 nm, Ir only), bypassing 1dσ*pσ. Most excited-state conversion and some relaxation steps are accompanied by direct decay to the ground state that is especially pronounced for the most flexible long/eclipsed Rh(dimen) conformer.

Publisher's Version