Absorption and fluorescence properties of rhodamine B in submono-, mono-and multilayer systems adsorbed on fused quartz plates have been studied at 295 and 77 K. Existence of fluorescent and nonfluorescent dimers of rhodamine B at 295 K and a structural change of the aggregate geometry at low temperatures have been postulated. Rates of nonradiative decay and photoinduced electron transfer of dimers adsbrbed on organic crystals and their possible role in hole injection are discussed.

Fluorescence anisotropy decay microscopy was used to determine, in individual living cells, the spatial monomer-dimer distribution of proteins, as exemplified by herpes simplex virus thymidine kinase (TK) fused to green fluorescent protein (GFP). Accordingly, the fluorescence anisotropy dynamics of two fusion proteins (TK27GFP and TK366GFP) was recorded in the confocal mode by ultra-sensitive time-correlated single-photon counting. This provided a measurement of the rotational time of these proteins, which, by comparing with GFP, allowed the determination of their oligomeric state in both the cytoplasm and the nucleus. It also revealed energy homo-transfer within aggregates that TK366GFP progressively formed. Using a symmetric dimer model, structural parameters were estimated; the mutual orientation of the transition dipoles of the two GFP chromophores, calculated from the residual anisotropy, was 44.6 +/- 1.6 degrees, and the upper intermolecular limit between the two fluorescent tags, calculated from the energy transfer rate, was 70 A. Acquisition of the fluorescence steady-state intensity, lifetime, and anisotropy decay in the same cells, at different times after transfection, indicated that TK366GFP was initially in a monomeric state and then formed dimers that grew into aggregates. Picosecond time-resolved fluorescence anisotropy microscopy opens a promising avenue for obtaining structural information on proteins in individual living cells, even when expression levels are very low.

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Measurement of the absolute phase of the surface second-harmonic light field with respect to the pump field, i.e. the phase of the surface non-linear susceptibility, is described. From such studies the absolute orientation of surface molecules can be determined. In the present work the liquid/vapor interface of an aqueous phenol solution was investigated.