Prospects for useful fission from singlet states higher than S in aggregated organic chromophores.

The few known reports and the likely prospects of finding new efficient routes to exciton fission from higher excited singlet states, S ( > 1), are reviewed. Aggregates of molecules that have large S-S electronic energy spacings and/or emit measurable "contra-Kasha" emission may offer further opportunities. Among these, electronically excited molecular systems that exhibit known efficient (T + T) triplet-triplet annihilation producing S could exhibit efficient singlet fission in aggregates when appropriately substituted to meet the necessary energy requirements.

Photophysics of Zinc Porphyrin Aggregates in Dilute Water-Ethanol Solutions.

Dimeric and multimeric aggregates of a model metalloporphyrin, zinc tetraphenylporphyrin (ZnTPP), have been produced in a controlled manner by incrementally increasing the water content of dilute aqueous ethanol solutions. Steady state absorption, fluorescence emission, and fluorescence excitation spectra have been measured to identify the aggregates present as a function of solvent composition. The dynamics of the excited states of the aggregates produced initially by excitation in the Soret region have been measured by ultrafast fluorescence upconversion techniques.