Photoreactivities of donor-acceptor crystals between 3,5-dinitrobenzoic acid and N-alkylcarbazoles

A variety of 1:1 charge-transfer (CT) crystals were prepared by using mainly dinitrobenzoic acids (as the acceptor) and carbazoles (as the donor). Most of the CT crystals prepared from 3,5-dinitrobenzoic acid (3) and a series of N-alkylcarbazoles (1a1h) underwent photoredox reactions initiated by the excited nitro group, leading to α-oxidation of N-alkyl groups (13 -15). The reactions were much more efficient in the solid state than in solution. These solid-state photoreactivities could be, on the whole, correlated with the C⋯O distances between the carbazole N-α-carbon atom and the nitro oxygen atoms nearby.