The Behavior of Exciplex Decay Processes and Interplay of Radiationless Transition and Preliminary Reorganization Mechanisms of Electron Transfer in Loose and Tight Pairs of Reactants

Abstract

Exciplex emission spectra and rate constants of their decay via internal conversion and intersystem crossing are studied and discussed in terms of conventional radiationless transition approach. Exciplexes of 9-cyanophenanthrene with 1,2,3-trimethoxybenzene and 1,3,5-trimethoxybenzene were studied in heptane, toluene, butyl acetate, dichloromethane, butyronitrile, and acetonitrile. A better description of spectra and rate constants is obtained using 0-0 transition energy and Gauss broadening of vibrational bands rather than the free energy of electron transfer and reorganization energy. The coincidence of parameters describing exciplex emission spectra and dependence of exciplex decay rate constants on energy gap gives the evidence of radiationless quantum transition mechanism rather than thermally activated medium reorganization mechanism of charge recombination in exciplexes and excited charge transfer complexes (contact radical ion pairs) as well as in solvent separated radical ion pairs. Radiationless quantum transition mechanism is shown to provide an appropriate description also for the main features of exergonic excited-state charge separation reactions if fast mutual transformations of loose and tight pairs of reactants are considered. In particular, very fast electron transfer (ET) in tight pairs of reactants with strong electronic coupling of locally excited and charge transfer states can prevent the observation of an inverted region in bimolecular excited-state charge separation even for highly exergonic reactions.

Magnetic Field-Sensitive Radical Pair Dynamics in Polymethylene Ether-Bridged Donor–Acceptor Systems

“…The vibronic transitions with Gaussian band shape of the exciplex were extracted by employing a model as described in refs. 8,45 The fluorescence spectrum of the locally excited fluorophore was directly accessible from the spectrum in the absence of the quencher moiety.…”

The Excited‐State Lifetimes in a G⋅C DNA Duplex are Nearly Independent of Helix Conformation and Base‐Pairing Motif

“…Although nonadiabatic theory has been used to describe charge recombination in some contact ion pairs,[30] this approach may fail for exciplexes having only partial electron transfer character. [31, 32]…”

Spectral and thermodynamic properties for the exciplexes of N-alkyl carbazoles with dicyanobenzenes in THF

“…Clear understanding can be collected about the energy difference of vibronic levels (DE CR ) and the energy of the dominant high-frequency vibration, and the information about the radiative behavior of exciplex can be obtained from the emission spectra. In order to gain this information fitting of the isolated emission spectra of exciplex according to Kuzmin's model of self-consistent polarization over a range of temperatures was done [22,23]. In this model, the emission line shape is given as a sum of vibronic transitions with Gaussian band shape by the following expression [22,23]:…”

“…In order to gain this information fitting of the isolated emission spectra of exciplex according to Kuzmin's model of self-consistent polarization over a range of temperatures was done [22,23]. In this model, the emission line shape is given as a sum of vibronic transitions with Gaussian band shape by the following expression [22,23]:…”