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When two objects are in contact, the force necessary for one to start sliding over the other is larger than the force necessary to keep the sliding motion going. This difference between static and dynamic friction is thought to result from a reduction in the area of real contact upon the onset of slip. Here, we resolve the structure in the area of contact on the molecular scale by means of environment-sensitive molecular rotors using (super-resolution) fluorescence microscopy and fluorescence lifetime imaging. We demonstrate that the macroscopic friction force is not only controlled by the area of real contact but also controlled by the “quality” of that area of real contact, which determines the friction per unit contact area. We show that the latter is affected by the local density of the contacting surfaces, a parameter that can be expected to change in time at any interface that involves glassy, amorphous materials.

Highly reflecting nanostructures of pseudoisocyanine J aggregates in a thin polymer film are prepared. Simultaneous atomic force microscope and reflection microscopic studies show a high degree of correlation between structural and optical properties on submicrometer scales. As a result of strong coupling between light and the aggregate excitonic states, optical modes evolve in the polariton-like reflectance spectra of the aggregate nanostructures which function as self-assembled optical microcavities.

A broad fluorescence band red-shifted from the absorption line of J-aggregate of pseudoisocyanine chloride in thin films of poly(vinyl sulfate) has been investigated. The fluorescence originates from traps populated by energy transfer from the excitonic band of the J-aggregate. The shift of the fluorescence maxima and the decrease of its intensity with increasing temperature have been explained by interaction of the trap with a 39 cm^-1 phonon mode. Spectral hole burning study shows that the traps are functionally associated with the whole J-aggregate fiber rather than with individual coherently coupled segments of the aggregate.

We present a new system for single-molecule detection at cryogenic temperatures, benzodiphenanthrobisanthene in a Shpolskii matrix of n-tetradecane. Most of the single-molecule lines are broader than the lifetime-limited value of 31.0 MHz, indicating the presence of spectral diffusion in the crystalline sample. For the detection of the fluorescence signal, we use a gradient index lens in a back-illumination configuration.

Net photosynthetic rate (PN), productivity and the first phases of the fluorescence induction curve were investigated in leaves of two potato cultivars exposed to water stress. Water stress applied to potato plants at the beginning of their development (planting-bud formation) increased productivity but decreased PNand variable fluorescence (Fv) of leaves. The short-term influence of water stress on the same plants also diminished the Fv.