Nanoviscosity effect on the spin chemistry of an electron donor/Pt-complex /electron acceptor triad - classical and quantum kinetics interpretation

Abstract

The magnetic-field dependent charge recombination kinetics upon ns-laser flash photolysis of a novel triarylamine/cyclometalated platinum complex/napthalenediimide triad (DPtA) have been measured in tetrahydrofuran (THF) and polytetrahydrofuran (pTHF) to study the spinchemical effect of a large increase of the macroviscosity of the solvent by a factor of about 1000. The magnetic-field dependence of the decay kinetics of the charge separated state has been accurately reproduced by a classical kinetic model, wherein the rate constants of transitions between spin substates of different Zeeman energy are represented by a single magnetic-field dependent rate constant k_±. In THF, the magnetic-field dependence of k_± is given by a double Lorentzian function which, in a double log plot, shows two characteristic steps that can be consistently assigned to the magnetic field inhibition of the coherent and incoherent i.e. relaxational spin mixing mechanism. In pTHF, the magnetic field effect on k_± is a single step function decreasing to its limiting value at about 5 times lower fields than in THF. As shown by a quantum theoretical simulation, in this solvent coherent and incoherent processes are contributing equally at all fields. The nanoviscosity of pTHF appears to be much smaller than its macroviscosity.

GRAPHICAL ABSTRACT

KEYWORDS:

• Photoinduced electron transfer
• spin chemistry
• donor acceptor systems
• polymer nanoviscosity

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Deutsche Forschungsgemeinschaft within the Graduate Research School GRK 2112 and the Bavarian Ministry of Education, Culture, Research, and the Fine Arts within the Solar Technologies Go Hybrid Consortium. N. L. is grateful to the Russian Foundation for Basic Research Reseach [grant number ‘17-03-00656’] and to the Federal Agency of Scientific Organizations of Russian Federation [grant number 0333-2017-0002] for the financial support.