New generation of fluorescence probes exhibiting charge-transfer reactions

With the advent and development of time-resolved spectroscopic technique and substantial progress in understanding of photophysical and photochemical events in condensed phases, a new goal may be achieved: modeling of biochemical reaction or its elementary step by a photochemical event occurring within the probe, bound to protein molecule. The probe may be located in a well-determined site of the protein matrix and report on the modulation of the reaction rate by the matrix and by the surrounding solvent, or by interactions in multiprotein complexes and in biomembranes. The advantage of this approach is obvious: in contrast to ordinary biochemical reaction, the excited-state reaction may be started by a short light pulse, and its development may be observed directly with high resolution in time. If the reaction rate is influenced by the dynamics of the protein matrix, these dynamics may be studied simultaneously with the reaction, by the same or similar probe, and within the same time range. In this report we discuss shortly the prospects for application of probes exhibiting electron transfer, twisted intramolecular charge transfer, and isomerizations. In the studies of electron-transfer dynamics of bianthryl in the complex with albumin and anti-bianthryl antibodies we show that the reaction is controlled by the dynamics of protein matrix which is found to be slower than nanosecond. The general problem of photochemical modeling of biochemical reactions is discussed.