Three isomers of a new C60-TTF dyad-C60-X-TTF (X = ortho, meta, and para)-have been synthesized by changing the linking positions (ortho, meta, and para) at a phenyl group that is attached to the methano-fullerene. The dyads showed clear intramolecular charge transfer (CT) absorption bands in the steady-state absorption spectra, which was indicative of an intramolecular CT interaction between the C60 and TTF moieties in the ground state. The increase in intensity of the CT absorption bands followed the order C60-ortho-TTF > C60-meta-TTF ≫ C60-para-TTF, which can be reasonably explained by the optimized molecular structures that are calculated at the ab initio level. Extreme quenching of the fluorescence intensity from the locally excited C60 moiety was observed to follow the aforementioned order, which suggests that very fast excited singlet-state dynamics are dependent on the isomers. The quenching of the absorption intensities of the triplet state of the C60 moiety detected in the nanosecond region was also observed to follow the same order, which suggests that competitive paths that are more efficient than intersystem crossing are present. From subpicosecond transient absorption measurements, very short-lived transient absorption bands attributed to the overlap of S1-Sn with the excited CT state that has strong CT character were obtained for C60-ortho-TTF (and C60-meta-TTF); appreciable charge-separated (CS) species were generated for C60-para-TTF. The lifetimes of the CT and CS states increased in the order of C60-ortho-TTF < C60-meta-TTF < C60-para-TTF. Overall, it was revealed that the ground and excited states are controlled by the difference in proximity between the C60 and TTF moieties, depending on the linking positions.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry