Ultrafast Infrared Spectroscopy of Vibrational States Prepared by Photoinduced Electron Transfer in (CN)₅FeCNRu(NH₃)₅^-

Abstract

The picosecond time-resolved infrared spectra of (CN)5FeCNRu(NH3)5 - were collected following optical excitation and reverse electron transfer. The measured reverse electron transfer rates are greater than 3 × 1012 s-1. In both formamide and deuterated water solutions, vibrational excitation in CN stretch modes is found after reverse electron transfer. The transient spectra at both earlier (1−35 ps) and later (10 ns) times give evidence of environment−solute coupling that can be accounted for by solvent heating and ion pair dynamics. A simulation of the spectral dynamics in formamide solution is presented using a kinetic model for vibrational excitation and relaxation. The simulation includes minor excitation in vibrational modes consistent with resonance Raman derived Franck−Condon factors, but it is also found that a nontotally symmetric mode is equally important as an acceptor.

Measuring Coherently Coupled Intramolecular Vibrational and Charge-Transfer Dynamics with Two-Dimensional Vibrational–Electronic Spectroscopy

“…Previous work has assigned the electronic transition in FeRu to be a MMCT excitation from the Fe II to the Ru III , resulting in Fe III and Ru II . 22 As shown in Fig. 1d (Fig.…”

“…[17][18][19][20][21][22][23][24][25] Transient IR, optical, and resonance Raman studies of FeRu in polar solvents have suggested the 7 involvement of some of the high frequency ν CN vibrations in the charge transfer process 19,23 and significant excitation in the ν CN modes upon ultrafast back electron transfer. 22 We have extensively studied the vibrational anharmonic couplings among ν CN modes and the role of solvent in modulating the molecular structure, anharmonic couplings, and the oxidation states of the metals in the FeRu complex. [26][27] This work introduces 2D VE spectroscopy to connect the complementary electronic and vibrational spectroscopic signatures collected previously in FeRu.…”

Femtosecond Multicolor Pump−Probe Study of Ultrafast Electron Transfer of [(NH3)5RuIIINCRuII(CN)5]- in Aqueous Solution

“…28 In an analogous system where one of the Ru atoms is replaced with Fe, the bridging and terminal CN stretching modes showed relaxation times on the order of picoseconds in D 2 O using 200 fs pulses. 29 It is possible, however, that significant portion of the vibrational relaxation occurs also on a similar time scale as solvation RuRu in water, and that this component of vibrational relaxation was not too fast to be resolved by the published infrared spectroscopy experiments (which had a resolution of several hundred femtosecond or longer). It is also possible is that the vibrational excess energy is distributed to FranckCondon inactive modes and is not observed spectroscopically.…”

Investigating vibrational anharmonic couplings in cyanide-bridged transition metal mixed valence complexes using two-dimensional infrared spectroscopy

“…Transient IR studies of the FeRu molecule and its analogues find a high degree of vibrational excitation in the ν CN modes upon ultrafast back electron transfer (BET). 14,15,18 The role of the ν CN modes in the metal-to-metal charge transfer (MMCT) excitation, and subsequent BET, of FePtFe dissolved in D 2 O has also been recently studied using various nonlinear spectroscopies. 20,21,26 These studies have found >6 quanta of vibrational energy deposited into the ν b mode following BET and provided experimental evidence that ν CN modes are both coherently and incoherently coupled to the charge transfer reaction.…”