P.R. Hania

Cylindrical Aggregates of 5,5',6,6'-Tetrachlorobenzimida- carbocyanine Amphiphilic Derivatives: Structure-Related Optical Properties and Exciton Dynamics

The static and time-resolved optical response of 5 , 5 ′ , 6 , 6 ′ -tetrachlorobenzimidacarbocyanine chromophore-based tubular double-wall molecular aggregates is studied. The linear dichroism and absorption spectra have the same basic structure for all aggregates investigated essentially showing a set of narrow and highly polarized bands originating from inner and outer wall excitations. The exact positions and strengths of absorption bands are influenced by the choice of side groups and various additives. Time-resolved fluorescence measurements show a substantial speeding of the fluorescence decay upon aggregation, mainly resulting from collective effects. Pump-probe experiments evidence slow inner-to-outer and fast outer-to-inner wall energy transfers between the walls of the tubules.

Ultrafast exciton transport in organic nanotubes

The dynamics of exciton transport between the inner and outer walls of double-layer cylindrical aggregates is measured. Downhill transport is fast (275 fs) and excitation intensity independent. Uphill transport is much slower (3.5 ps), but this rate increases when the excitation density is raised. This suggests that exciton-exciton annihilation is involved.

Reaction dynamics and applications in patterning of bisthienylcyclopentene-based photochromic switches

The structural and optical properties of the gel-forming photochromic switch 1,2-bis(2’-methyl-5’-{{((R) phenylethyl)amino}carbonyl}thienyl-3’-yl)cyclopentene are studied by means of the linear absorption and holographic grating techniques. The use of diffractive optics enables recording of holographic gratings with high long-term phase stability. The diffraction efficiency of the recorded holographic gratings approach values of 30% for low writing beam energies when diffusion is the rate determining factor. At higher writing pulse energies the competition between the diffusion and photodecomposition processes causes lower diffraction efficiencies. At irradiation doses above 10 mJ the spatial profile of the recorded gratings is strongly influenced by saturation effects. Because of the well-determined grating profile the holographic grating technique is potentially applicable for the quantitative characterisation of the diffusion process in photochromic gels.