Broadband Visible Light-Absorbing [70]Fullerene-BODIPY-Triphenylamine Triad: Synthesis and Application as Heavy Atom-Free Organic Triplet Photosensitizer for Photooxidation

A broadband visible light-absorbing [70]fullerene-BODIPY-triphenylamine triad (C(70)-B-T) has been synthesized and applied as a heavy atom-free organic triplet photosensitizer for photooxidation. By attaching two triphenylmethyl amine units (TPAs) to the π-core of BODIPY via ethynyl linkers, the absorption range of the antenna is extended to 700 nm with a peak at 600 nm. Thus, the absorption spectrum of C(70)-B-T almost covers the entire UV–visible region (270–700 nm). The photophysical processes are investigated by means of steady-state and transient spectroscopies. Upon photoexcitation at 339 nm, an efficient energy transfer (ET) from TPA to BODIPY occurs both in C(70)-B-T and B-T, resulting in the appearance of the BODIPY emission at 664 nm. Direct or indirect (via ET) excitation of the BODIPY-part of C(70)-B-T is followed by photoinduced ET from the antenna to C(70), thus the singlet excited state of C(70) ((1)C(70)(*)) is populated. Subsequently, the triplet excited state of C(70) ((3)C(70)(*)) is produced via the intrinsic intersystem crossing of C(70). The photooxidation ability of C(70)-B-T was studied using 1,5-dihydroxy naphthalene (DHN) as a chemical sensor. The photooxidation efficiency of C(70)-B-T is higher than that of the individual components of C(70)-1 and B-T, and even higher than that of methylene blue (MB). The photooxidation rate constant of C(70)-B-T is 1.47 and 1.51 times as that of C(70)-1 and MB, respectively. The results indicate that the C(70)-antenna systems can be used as another structure motif for a heavy atom-free organic triplet photosensitizer.