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RESEARCH PRODUCT

Molecular aggregates of quinuclidine and chlorophyll a

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description

A slightly polar molecule quinuclidine seems to form weakly bound aggregates in concentrated water solutions. Molecular dynamics simulation of a 6 mol water solution indicates clustering of quinuclidine molecules into an almost spherical structure with polar ends of the molecules pointing towards the solvent. Experimental evidence of aggregation was obtained by observing a small but obvious red shift of the o'' a absorption and a dramatic shortening of the fluorescence lifetime of the c n transition of concentrated solutions. The observed self-quenching is interpreted in terms of Frster model for energy transfer in the cluster. It is estimated that excitation may migrate on the cluster surface over a distance of two or three quinuclidine molecules before getting trapped. Chlorophyll a in dilute 3-methylpentane solutions forms water coupled dimers at reduced temperatures. Fluorescence lifetime of the monomer absorption is strictly single exponential while that of the aggregate absorption shows a non-exponential and increasingly faster decay at reduced temperatures. Temperature dependence is explained by increased interaction of the dimers at low temperatures. 2.