Synthesis and characterization of highly photoresponsive fullerenyl dyads with a close chromophore antenna-C_(60) contact and effective photodynamic potential

摘要

We report the synthesis of a new class of photoresponsive C_(60)-DCE-diphenylaminofluorene nanostructures and their intramolecular photoinduced energy and electron transfer phenomena. Structural modification was made by chemical conversion of the keto group in C_(60)(>DPAF-C_n) to a stronger electron-withdrawing 1,1-dicyanoethylenyl (DCE) unit leading to C_(60)(>CPAF-C_n) with an increased electronic polarization of the molecule. The modification also led to a large bathochromic shift of the major band in visible spectrum giving measureable absorption up to 600 nm and extended the photoresponsive capability of C_(60)-DCE-DPAF nanostructures to longer red wavelengths than C_(60)(>DPAF-C_n). Accordingly, C_(60)(>CPAF-C_n) may allow 2γ-PDT using a light wavelength of 1000-1200 nm for enhanced tissue penetration depth. Production efficiency of singlet oxygen by closely related C_(60)(>DPAF-C_(2M)) was found to be comparable with that of tetraphenylporphyrin photosensitizer. Remarkably, the ~1O_2 quantum yield of C_(60)(>CPAF-C_(2M)) was found to be nearly 6-fold higher than that of C_(60)(>DPAF-C_(2M)), demonstrating the large light-harvesting enhancement of the CPAF-C_(2M) moiety and leading to more efficient triplet state generation of the C_(60)> cage moiety. This led to highly effective killing of HeLa cells by C_(60)(>CPAF-C_(2M)) via photodynamic therapy (200 J cm~(-2) white light). We interpret the phenomena in terms of the contributions by the extended π-conjugation and stronger electron-withdrawing capability associated with the 1,1-dicyanoethylenyl group compared to that of the keto group.