Time-resolved delayed luminescence of chlorophyll alpha in anhydrous polymer systems

Absorption, fluorescence and time-resolved delayed luminescence spectra of chlorophyll a in thin anhydrous polymer matrices of polyvinyl alcohol and nitrocellulose have been measured. Delayed luninescence spectra were measured in the microsecond time range in the 600-800 nm region at different temperatures (8-300 K). Delayed luminescence kinetics for the following chlorophyll a species: monomeric form, chlorophyll-chlorophyll dimer and chlorophyll-nitrocellulose complex, have been obtained and decay times are evaluated (9-17 mu s). Decay times are found to be independent of temperature. The possible mechanisms responsible for delay luminescence are discussed. It is found that the delayed luminescence intensity slowly and linearly increases with decreasing temperature. Thermal repopulation of the singlet excited state of chlorophyll a from the triplet state together with annihilation processes have been excluded as mechanisms for generation delayed luminescence. Charge separation and ion recombination are discussed as more likely mechanisms of delayed luminescence. Delayed luminescence results are compared to those reported in the literature chlorophyll a under a variety of conditions.