Comparison of Singlet Oxygen Generation Efficiency between Water‐Soluble C60‐Diphenylaminofluorene Conjugates and Molecular Micelle‐like FC4S

Abstract

Amphiphilic C60‐diphenylaminofluorene conjugates C60 (>DPAF‐EGn) exhibit good water‐solubility and form self‐assembled bilayer vesicles in dilute aqueous solution. Their singlet oxygen generation efficiency in DMF or H2O was evaluated by using time‐resolved measurements of singlet oxygen luminescence at 1270 nm upon photoexcitation by nanosecond pulse laser operated at 523 nm. By the application of different bandpass filters to cut off certain emission at wavelength ranges outside 1270 nm, a distinguishable peak in medium to high integrated luminescence intensity was collected at wavelengths between 1240 and 1300 nm. It provided confirmation and close correlation of emitted photon counts measured for these fullerene derivatives to singlet oxygen. In contrast to apparently high singlet oxygen generation efficiency of FC4S in H2O, an observed low singlet oxygen production rate from aqueous solutions of C60 (>DPAF‐EG14) and C60 (>DPAF‐EG45) was interpreted as the result of the occurrence of competitive ultrafast intramolecular electron transfer going from DPAF moiety to C60 cage moiety. That eliminated largely the possibility of energy transfer process for fullerenyl intersystem crossing to generate 3C*60(>DPAF‐EGn). Instead, radical ion‐pairs containing molecules C60 −· [>(DPAF‐EGn)+·] were produced via the intramolecular electron transfer process in the photoexcited transient state.