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 pi-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 (C-1(70)*) is populated. Subsequently, the triplet excited state of C-70 (C-3(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.

Automated summary

A broadband visible light-absorbing fullerene-BODIPY-triphenylamine triad has been synthesized and applied as a heavy atom-free organic triplet photosensitizer for efficient photooxidation, showing higher efficiency than individual components and methylene blue. It extends the absorption range and demonstrates effective energy transfer processes leading to enhanced photooxidation rate.