SUPRAMOLECULAR AGGREGATES OF PHOTOREACTIVE AROMATICS - STRUCTURE, PHOTOPHYSICS AND PHOTOCHEMISTRY OF STILBENE AND AZOBENZENE PHOSPHOLIPIDS

Stilbene and azobenzene-derivatized phospholipids have been synthesize d as building blocks to study H-aggregate formation, structure and pro perties in both bilayer vesicles and LB films. The observed H-aggregat es in bilayers display similar spectral characteristics to that in LB films and a strong induced circular dichroism spectrum. Studies of int erconversion between H-aggregates and monomers or dimers have establis hed relatively small, integral numbers for aggregate sizes. Based on t hese results as well as molecular cooling simulation, chiral cyclic pi nwheel structures are proposed for these H-aggregates. Single crystal structure of a trans-stilbene derivative (4) has been obtained, and it s remarkable similarity in structure to compressed monolayer obtained from molecular simulation and almost identical spectra to H-aggregate of stilbene support the proposed herringbone lattice for these aggrega tes. The very large arrays of aggregates may consist of a ''mosaic'' o f small aggregates. The presence of aggregates as either stable or met astable entities has special consequences for microscopic as well as m acroscopic properties of the medium in which they are generated. The a ggregates of azobenzene in DPPC vesicles promote reagent release much more efficiently than the correspondent monomer and dimer. Trans-cis p hotoisomerization of azobenzene aggregates opens a convenient way to e stablish photoregulatable membrane and related materials.