Synthesis and characterization of highly photoresponsive fullerenyl dyads with a close chromophore antenna–C60 contact and effective photodynamic potential

摘要

We report the synthesis of a new class of photoresponsive C60–DCE–diphenylaminofluorene nanostructures and their intramolecular photoinduced energy and electron transfer phenomena. Structural modification was made by chemical conversion of the keto group in C60(>DPAF-Cn) to a stronger electron-withdrawing 1,1-dicyanoethylenyl (DCE) unit leading to C60(>CPAF-Cn) 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 C60–DCE–DPAF nanostructures to longer red wavelengths than C60(>DPAF-Cn). Accordingly, C60(>CPAF-Cn) 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 C60(>DPAF-C2M) was found to be comparable with that of tetraphenylporphyrin photosensitizer. Remarkably, the ¹O2 quantum yield of C60(>CPAF-C2_M) was found to be nearly 6-fold higher than that of C₆₀(>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 C₆₀> cage moiety. This led to highly effective killing of HeLa cells by C₆₀(>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.