The use of a tertiary solvent mixture to study solvent dynamic effects in the photoinduced electron transfer reaction of excited singlet pyrene and indole

Description

Photoinduced electron transfer (PET) plays an important role in many areas of chemistry. The physical properties of the solvent influence the rate constant of PET reactions in many ways. Classical electrodynamical description of the solvent reorganization energies in electron-transfer theories use the Pekar factor γ=(1/n2-1/ε) as a solvent parameter. Dielectric constant ε and refractive index n influence the solvent dipole reorientations and contribute to the activation energy of the electron transfer reactions [1]. That is why solvent-dependent measurements of ET reactions start quite early. But, electron-transfer kinetics is also influenced by diffusion and therefore by the solvent viscosity η. Unfortunately, most measurements published use different solvents in a not consequent way [2]. Results of polar and unipolar solvents are compared together with high- and low viscous ones. We present here the first results of experiments made in a series of solvent mixtures comprising propyl acetate, butyronitrile, and diethyl phthalate, spanning a wide range of dielectric constants, keeping the refractive index and the viscosity constant [3]. We used the PET reaction of singlet excited pyrene and indole whose solvent dependence is already described in the literature [2]. Quenching rate constants were obtained from Stern-Volmer plots based on both static and dynamic (TCSPC) measurements. Fluorescence lifetimes, quenching rate constants kq, and the ΔG-dependence of ln kq are reported for the solvent mixtures and compared with results reported in pure organic solvents [2].

[1] M. Berghold, J. Bächle, S. Landgraf, G. Grampp, ChemPhysChem, 18,128 (2017). [2] H. A. Montejano, J.J. Cosa, H.A. Garrera, C.M. Previtali, J. Photochem. Photobiol. A Chem. 86,115 (1995). [3] A. Wankmüller, M. Berghold, S. Landgraf, J. Mol. Liquids, 333, 115880 (2021).

Period	9 Sept 2022
Event title	Bunsen-Tagung 2022: Understanding Dispersion Interactions in Molecular Chemistry
Event type	Conference
Location	Gießen, Germany, HesseShow on map
Degree of Recognition	International