Fullerene exciplex emission

The extreme solvent sensitivity of the exciplex fluorescence is very interesting. Fullerene-amine exciplex emissions observed in saturated hydrocarbon solvents are absent in solvents such as benzene and toluene (27,84,88,101), which has been explained in terms of solvent polarizability effects [101]. However, there has also been an explanation [84] that the formation of exciplexes in a solvent such as benzene is hindered by specific solute-solvent interactions that result in complexation between the fullerene and solvent molecules. The two explanations are fundamentally different. In the former, the exciplex state is effectively quenched through a radiationless decay pathway facilitated by a stronger dielectric field of the solvent. However, the latter assumes that the ground state fiillerene-solvent complexation prevents the formation of fullerene-donor exciplexes. In order to understand whether the extreme solvent sensitivity is solvent specific (limited to benzene, toluene, and other aromatic solvents) or solvent property specific (solvent polarity and polarizability), fluorescence spectra of C70-DEA were measured systematically in mixtures of hexane and a polar solvent (acetone, THF, or ethanol) with volume fraction up to 10% [101]. The results are consistent with the explanation of solvent polarity and polarizability effects. 

In saturated hydrocarbon solvents such as methylcyclohexane and hexane, quenchings of fullerene fluorescence by aromatic amines result in the formation of emissive fullerene-amine exciplexes [8,84,88,95]. The exciplex fluorescence spectra are red-shifted from those of free fullerenes (Fig. 31). The... 

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