<title>Biochemical diagnostics by excited state absorption spectroscopy</title>

Abstract

Excited state absorption (ESA) spectroscopy test electronic transitions from the first excited states to higher ones. These transitions are often much more sensitive to the environment of the specimen under investigation than ground state absorption spectra as well as fluorescence spectra. Therefore ESA on intermolecular interactions becomes a candidate for efficient biochemical sensors. In addition, many applications where fluorescence probes are used today may be improved in future regarding sensitivity and velocity by the use of ESA, because absorptive measurements principally allow much faster detection in comparison to fluorescence. Two examples are given: on one hand photoinduced intramolecular electron transfer reactions in special pyrenylbenzene compounds were proven to be strongly dependent on environmental conditions are polarity, for example. Moreover, intermolecular electron transfer to the neighborhood was identified by this technique. On the other hand the denaturation of myoglobin is observed by ESA spectroscopy on fluorescein probes covalently bound to be protein. During unfolding the protein the local environment of the probes changes, which si reflected effectively in the spectra. In both examples the ESA method is compared to traditional fluorescence techniques. Besides the confirmation of the traditionally obtained results, valuable new information is yielded.