TY - JOUR

T1 - Nanoviscosity effect on the spin chemistry of an electron donor/Pt-complex /electron acceptor triad - classical and quantum kinetics interpretation

AU - Riese, Stefan

AU - Mungenast, Lena

AU - Schmiedel, Alexander

AU - Holzapfel, Marco

AU - Lukzen, Nikita N.

AU - Steiner, Ulrich E.

AU - Lambert, Christoph

PY - 2019/10/2

Y1 - 2019/10/2

N2 - 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.

AB - 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.

KW - donor acceptor systems

KW - Photoinduced electron transfer

KW - polymer nanoviscosity

KW - spin chemistry

KW - GEMINATE RECOMBINATION

KW - MAGNETIC-FIELD DEPENDENCE

KW - COHERENT

KW - PHOTOCHEMISTRY

KW - RELAXATION

KW - CHEMICAL CONTROL

KW - MODEL

KW - RADICAL-PAIR

UR - http://www.scopus.com/inward/record.url?scp=85052946638&partnerID=8YFLogxK

U2 - 10.1080/00268976.2018.1511867

DO - 10.1080/00268976.2018.1511867

M3 - Article

AN - SCOPUS:85052946638

VL - 117

SP - 2632

EP - 2644

JO - Molecular Physics

JF - Molecular Physics

SN - 0026-8976

IS - 19

ER -