Two-photon two-color excited polarized fluorescence in biologically relevant molecules: investigation of molecular excited state structure and dynamics

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In the framework of a joint research project the alignment, orientation and rotational correlation time of biological relevant molecules will be studied. The molecules will be aligned and oriented using two color two photon (2c2p) laser pulses under different polarization schemes (here tunable radiation around 400nm and 800nm). The fluorescence is observed for different polarization angle as well. The advantage of using two different photons is twofold: shorter wavelengths (down to 265nm) can be reached making label-free proteine detection possible and different alignments of the molecules become possible compared to two photon excitation using identical photons. Due to diffusion processes, the initial aligned molecules will finally be distributed isotropically. We intend to determine the corresponding rotational correlation time which contains information on the interaction of the molecule with its surrounding. In a proof of principle PTP was investigated. The research work will be focused on the study of tryptophan, as characteristic chromophore for probing proteins, and indole, a molecule which shows some unusual spectroscopic features. In addition, some 2c2p experiments on indole have been performed by other groups. The results will be theoretically and experimentally supported by the research group of O. Vasyutinskii.