Synthesis and Photoinduced Electron Transfer Studies of a Tri(Phenothiazine)–Subphthalocyanine–Fullerene Pentad

A novel donor–acceptor pentad featuring subphthalocyanine and fullerene as the primary electron donor and acceptor, and three phenothiazine entities as secondary hole transferring agents, have been newly synthesized and characterized as an photosynthetic reaction center model compound. Occurrences of ultrafast photoinduced electron transfer (PET) and slower charge recombination are witnessed in the pentad from the femtosecond and nanosecond transient absorption studies

Control over Photoinduced Energy and Electron Transfer in Supramolecular Polyads of Covalently linked azaBODIPY-Bisporphyrin ‘Molecular Clip’ Hosting Fullerene

A ‘molecular clip’ featuring a near-IR emitting fluorophore, BF₂-chelated tetraarylazadipyrromethane (aza-BODIPY) covalently linked to two porphyrins (MP, M = 2H or Zn) has been newly synthesized to host a three-dimensional electron acceptor fullerene via a ‘two-point’ metal–ligand axial coordination. Efficient singlet–singlet excitation transfer from ¹ZnP* to aza-BODIPY was witnessed in the dyad and triad in nonpolar and less polar solvents, such as toluene and <i>o</i>-dichlorobenzene, however, in polar solvents, additional electron transfer occurred along with energy transfer. A supramolecular tetrad was formed by assembling bis-pyridine functionalized fullerene via a ‘two-point’ metal–ligand axial coordination, and the resulted complex was characterized by optical absorption and emission, computational, and electrochemical methods. Electron transfer from photoexcited zinc porphyrin to C₆₀ is witnessed in the supramolecular tetrad from the femtosecond transient absorption spectral studies. Further, the supramolecular polyads (triad or tetrad) were utilized to build photoelectrochemical cells to check their ability to convert light into electricity by fabricating FTO/SnO₂/polyad electrodes. The presence of azaBODIPY and fullerene entities of the tetrad improved the overall light energy conversion efficiency. An incident photon-to-current conversion efficiency of up to 17% has been achieved for the tetrad modified electrode

Bisdonor–azaBODIPY–Fullerene Supramolecules: Syntheses, Characterization, and Light-Induced Electron-Transfer Studies

Achieving ultrafast light-induced charge separation requires carefully selected donor and acceptor entities often held together in a closer proximity. In the present investigation, two tetrads featuring a near-IR-emitting sensitizer, BF₂-chelated dipyrromethene (azaBODIPY), covalently linked to a fullerene through the central boron atom and two electron-donor entities, namely, <i>N</i>,<i>N</i>-dimethylaminophenyl, or bithiophene in close proximity to the fullerene entity were designed and synthesized, and the results were compared to the earlier-reported bisferrocene–azaBODIPY–fullerene tetrads in this series. The tetrads synthesized by establishing a multistep procedure exhibited typical spectral, redox, and photo reactivities of the individual components with some degree of intramolecular interaction. The X-ray structure of one of the precursor triads was also solved as part of this investigation. Ultrafast photoinduced electron transfer was witnessed in the case of both tetrads by femtosecond transient absorption spectroscopy studies. The significance of electron-donor entities was clear for the tetrad derived from <i>N</i>,<i>N</i>-dimethylaminophenyl entities, while for the bithiophene-derived tetrad, the charge separation involved mainly the azaBODIPY and fullerene entities. The charge recombination process involved populating the triplet excited state of azaBODIPY prior to returning to the ground state for both tetrads, as demonstrated by nanosecond transient absorption studies