Effect of laser intensity on the determination of intermolecular electron transfer rate constants—Observation of Marcus inverted region in photoinduced back electron transfer reactions

Abstract

The light intensity and concentration dependence of the photoproduct yield are investigated in a monophotonic process. The relationship of the photoproduct yield with the laser intensity and the complex concentration for a monophotonic process is derived under laser flash photolysis. The relationship is confirmed experimentally in a monophotonic process, i.e., triplet-triplet transition for a Cu͑I͒ complex Cu 6 ͑DMNSNЈ͒ 6 (DMNSNЈϭ4,6-dimethylpyrimidine-2-thiolate). At low light intensity, the relationship can be approximated by a linear inverse square root dependence on the light intensity. Based on this equation, a method is proposed to determine the intrinsic back electron transfer rate constant k ET b in photoinduced intermolecular electron transfer reactions, precluding the effect from the diffusional encounter pairs. The Marcus ''inverted region'' is observed by using the method in photoinduced back electron transfer reactions of ͓Au 2 ͑dppm͒ 2 ͔͑ClO 4 ͒ 2 (dppmϭbis͑diphenylphosphino͒methane) with a series of substituted pyridinium acceptors.

Resonance Raman Investigation of the Au(I)−Au(I) Interaction of the 1[dσ*pσ] Excited State of Au2(dcpm)2(ClO4)2 (dcpm = Bis(dicyclohexylphosphine)methane)

“…Luminescent gold(I) compounds, and in particular those with intramolecular gold−gold interactions, have been receiving intense interest from different perspectives. − Extensive photoluminescence measurements have been made on this class of compounds, and in many instances the relationship between aurophilicity (i.e., gold−gold bonding) and the emission energies has been stated . It has also been reported that dinuclear and polynuclear gold(I) compounds with bridging phosphine ligands have long-lived emissive excited states which are powerful photoreductants with E ° values ranging from −1.6 to −1.7 V vs SCE 5f,6a Indeed, interesting photochemistry has been reported for the [Au 2 (dppm) 2 ] 2+ (dppm = bis(diphenylphosphine)methane) complex which catalyzes reductive C−C bond coupling from alkyl halides upon photoexcitation with UV light and in the presence of sacrificial electron donors 5b…”

“…Like d 8 −d 8 metal complexes, metal−metal interaction in dinuclear gold(I) compounds leads to an intense low-energy n dσ* → ( n + 1)pσ transition, which red-shifts in energy from the n dσ* → ( n + 1)pσ transition of its mononuclear counterparts. ,5a, Here, the n dσ* refers to the antibonding combination of n d z 2 and ( n + 1)pσ to the bonding combination of the ( n + 1)p z orbitals. The prototype example of dinuclear gold(I) compounds is [Au 2 (dppm) 2 ] 2+ , which exhibits an intense 5dσ* → 6pσ transition at 297 nm. ,5a In solution, this compound shows a long-lived photoluminescence at 570 nm, which was assigned to come from the 3 [dσ*pσ] excited state. Recent molecular orbital studies revealed that such an assignment needs to be revised .…”

Multi-channel lock-in amplifier assisted femtosecond time-resolved fluorescence non-collinear optical parametric amplification spectroscopy with efficient rejection of superfluorescence background

“…This value is apparently larger than the generally observed diffusionlimited bimolecular rate constant at room temperature in an order of 10 10 s −1 M −1 . 49 the singlet-excited state rhodamine 6G is only 1/18 of that of the ground state. 50 Therefore, the observed larger secondorder rate constant for the formation of the excimer cannot be interpreted by the diffusion rate constant of the singletexcited state molecule, instead the much larger rate constant also points to the formation of the ground-state loosely bound pair.…”

Copper(i) pyrimidine-2-thiolate cluster-based polymers as bifunctional visible-light-photocatalysts for chemoselective transfer hydrogenation of α,β-unsaturated carbonyls

“…These emissions are most probably arising from a ligand-to-metal charge-transfer (LMCT) and/or metal-to-ligand charge-transfer (MLCT), possibly involving metal-centered (ds/dp) states. 49,50 The solid-state emission spectra of 2 and 3 were investigated at room temperature with excitation at 420 nm (Fig. S7 † ).…”