Charge recombination reactions in photoexcited fullerene C<SUB>60</SUB>-amine complexes studied by picosecond pump probe spectroscopy

Photoexcitation of complexes between fullerene C60 and organic amines in benzene solutions is known to result in charge separation (CS) and subsequent charge recombination (CR) reactions, which lead to varying yields of fullerene triplet formation. Picosecond flash photolysis studies are carried out on C60-diphenylamine (DPA), C60-triethylamine (TEA), C60-diazabicyclooctane (DABCO), and C60-triphenylamine (TPA) systems to find out mechanistic details of the triplet formation on CR by inducing heavy atom and polarity effects by using suitable solvents. It is found that in the case of C60-DPA, C60-TEA, and C60-DABCO systems proton transfer from the amine cation to the C60 anion in the ion pair state dominates, leading to poor triplet yields, which improve in heavy atom containing solvents.In TPA, proton transfer is not possible and hence fullerene triplet yields are high. Increase of solvent polarity for this system results in decreased C60 triplet yields with a consequent increase in the ion dissociation yield. A suitable reaction scheme is proposed to explain the results obtained