Some excited state charge-transfer interactions.

The intramolecular excited state interactions of polycyclic aromatic hydrocarbons and halogens have been studied where the aromatic nucleus is separated from the auencher by numerous linking chains. The effects of the interactions on the various aromatic decay parameters are-explained in terms of excited complex formation rather than simple heavy atom theory. Mechanisms for formation of the complexes are discussed and correlated with the different derivatives used in the study. The reactivity of the carbon-halogen bond is found to have a considerable importance on the effects observed, particularly in relation to work at low temperature and studies of the triplet yields. The work, was extended to include the interactions of a variety of amines with aromatic nuclei by means of similar series of derivatives. The geometrical requirements for excited complex formation are discussed in depth and the conclusion is reached that amine exciplexes require very loose qeometries in relation to excited dimers. Finally the excited state interactions of several photosensitisers with a large number of quenchers have been examined. Excited singlet state quenching is shown to be a general phenomenon and the quenching constants are reported for many aromatic hydrocarbon derivatives, amines and anions. The interactions are shown to be dependent on the ionisation potential of the quencher. An important interaction of [beta]-carotene and the excited singlet state of chlorophylla is reported, together with some interactions of photosensitiser triplet states.