Tuning Optical and Electron Donor Properties by Peripheral Thio–Aryl Substitution of Subphthalocyanine: A New Series of Donor–Acceptor Hybrids for Photoinduced Charge Separation

Subphthalocyanine (SubPc), a unique ring‐reduced member of the common phthalocyanines family, although known for its higher absorptivity, reveals narrow absorption with peak maxima around 570 nm thus limiting its utility in light‐energy‐harvesting applications. In the present study, by peripheral thio–aryl substitution of SubPc macrocycle, the spectral properties have been modulated to extend the absorption and emission well into the visible/near‐IR region. Additionally, for α‐ring‐substituted derivatives, facile oxidation of SubPc was witnessed, thus making these derivatives better electron donors. Next, the preparation of donor–acceptor dyads containing the well‐known electron acceptor C₆₀ connected to the central boron atom of SubPc was accomplished by making use of the 1,3‐dipolar cycloaddition reaction. Control experiments and free‐energy calculations using the redox and spectral data suggested that the observed fluorescence quenching of SubPc in these dyads is due to electron transfer. Accordingly, transient spectral studies performed both in polar and nonpolar solvents conclusively proved electron transfer to be the quenching mechanism in these dyads. The measured rate constants by fitting kinetic data revealed efficient charge separation and charge recombination processes, suggesting that these dyads could be useful materials for the construction of light‐to‐electricity or light‐to‐fuel production devices.