Substituted stilbenes: A new view on well-known systems: New applications in chemistry and biophysics

In this review, we present new areas of application of stilbene compounds in chemistry and biophysics. The first is the application of the linear free-energy relationships (LFER) to photochemistry of substituted stilbenes. The second is the development of the fluorescence-photochrome technique for investigation of different dynamical processes in biological membranes and surface systems. The various time-scale processes occurring with the stilbene molecules after irradiation were found to exhibit different sensitivity to intramolecular donor-acceptor effects of substituents and medium polarity. The sensitivity is quantitatively characterised by ρ-constant of the linear Hammett-like relationships. The obtained experimental data on LFER has independently confirmed the Saltiel mechanism of the photoisomerisation and established the quantitative basis for detailed mechanistic analysis of the different stages of this important photochemical reaction. The measurements of the direct and sensitised trans-cis and cis-trans photoisomerisation allowed investigation the rotational and translational diffusion of the stilbene labels and their aromatic moieties labelled proteins in a wide temporal range. The cascade photochemical system based on the combination of the stilbene, triplet and nitroxide-spin probes gained an additional advantage to measure the rate constant of the triplet state quenching and to estimate the local concentration of stable radicals. High sensitivity, validity and relatively low cost of conventional fluorescence facilities are the main advantages of these fluorescent-photochrome methods.