10/9 - Seminar (physical): Michael Tauber, UC San Diego
Michael Tauber - Tauber Lab website
Department of Chemistry and Biochemistry
UC San Diego
Host: Haw Yang
Exciton fission and annihilation in organic molecular assemblies
The aggregation of chromophores can give rise to photophysical processes that are not available to a monomer. Singlet fission, whereby a singlet excited state forms two triplets on neighboring molecules, inherently depends upon intermolecular interactions. The mechanism is of special interest in part because it could lead to improved efficiencies of organic photovoltaics. We have investigated the excited-state dynamics of self-assembled organic molecules in the carotenoid and perylene diimide (PDI) families. A combination of time-resolved absorption and resonance Raman spectroscopy, along with steady-state methods, are utilized as probes of the excited- and ground-state properties of the aggregates. Spectra of the carotenoid aggregates support sub-picosecond formation of triplet excited states, and yields in the range of 70-200%. Both factors point to a singlet fission mechanism. Our observation of similar excited-state dynamics within small multimers of carotenoids in phospholipid bilayers leads us to propose a possible functional role of singlet fission in biology. In the case of the PDI aggregate, some of the spectroscopic data support triplet formation via a singlet fission mechanism. However, kinetic data are consistent with dynamics on a singlet excited-state surface. During the talk, these findings for various assemblies of organic molecules will be discussed in the context of general energetic and structural factors for singlet fission.