ИСТИНА

Proton transfer and electron transfer reactions are fastest chemical reactions since only rather small transformations of nuclear structure of reactant molecules are involved in the process of these reactions. They are important for creation of new probes and sensors for medicine and technical applications. In spite of formal similarity of electron and proton transfer some important distinctions exist between them. Fastest reactions (k ∼ 1012–1013 s–1) are observed only for ESET. They are controlled by electronic coupling matrix element and follow the radiationless transition mechanism and non-exponential kinetics. Rather wide rate distributions P(lnk) are related to the fluctuations of electronic coupling and distribution of the P(VAD2). Some slower ESET and ESPT reactions (k ∼ 1010–1012 s–1) are controlled by the medium and reactant molecules reorganization. Only these reactions can be described in terms of ordinary chemical kinetics (exponential kinetics and very narrow rate distribution (close to δ-function)). In this work we compare several important features of ultrafast ESPT and ESET reactions using the traditional and the rate distribution approaches. Many proton transfer reactions were shown to follow the ordinary exponential kinetics even in picosecond region. For ESET reactions one has to use a presentation of the decay kinetics N(t) in the form of the distribution functions P(lnk) since N(t) can be expressed only by polyexponential functions. These P(lnk) contain as a rule two bands corresponding to different mechanisms of ET (radiationless transition mechanism of ET with k ∼ 1012–1013 s–1 and Marcus mechanism controlled by the reorganization energy of the medium and reactants with k ∼ 1010–1012 s–1). The relationships between experimental values of the rates of ESPT and ESET and the reaction driving forces, medium polarity, viscosity, temperature are discussed.