Tripodal Triazine and 1,8-Naphthalimide-based Small Molecules as Efficient Photocatalysts for Visible-light Oxidative Condensation.

Tripodal donor-acceptor (D-A) small molecules Tr-Np3 and Tr-T-Np3 consisting of triphenyl triazine and 1,8-naphthalimide, without and with a thiophene spacer have been synthesized. Their optical and redox properties were thoroughly investigated along with their utilization as photocatalysts in organic transformations. Compounds Tr-Np3 and Tr-T-Np3 showed broad absorption in the range of 290-480 nm in solutions and 300-510 nm in thin films. These tripodal molecules displayed wide optical bandgaps of (E ) 3.10 eV and 2.64 eV with very deep-lying HOMO energy levels (-6.60 eV and -6.03 eV) and low-lying LUMO levels (-3.50 eV and -3.40 eV). Appreciable electron mobilities of 5.24×10  cm /Vs and 6.14×10  cm /Vs were obtained for compounds Tr-Np3 and Tr-T-Np3 respectively by space-charge limited current (SCLC) measurements. Metal-free tripodal molecules Tr-Np3 and Tr-T-Np3 showed excellent photocatalytic abilities towards condensation of aromatic aldehydes and o-phenylenediamine followed by cyclization under visible light to yield benzimidazole derivatives that are of high medicinal value.