Synthesis, physicochemical properties and theoretical calculations of a subphthalocyanine peripherally substituted by multiple anthryl-ethynyl-aniline moieties

We report here the synthesis of a novel C-3-subphthalocyanine (SubPc)-based electron donor-acceptor conjugate (1) in which the macrocycle has been functionalized at its peripheral positions with three anthryl-ethynyl-N,N-dimethylaniline groups. The latter moiety, besides conferring increased stability and solubility to the resulting system, substantially broadens its absorption capability. In-depth spectroscopic, spectrometric, and electrochemical analyses as well as theoretical calculations carried out on 1 suggest a moderate ground state intramolecular interaction between the macrocycle and the orthogonally-arranged anthryl-ethynyl-N,N-dimethylaniline moieties. Interestingly, such electronic communication significantly increases in the excited state in a process strongly depending on the polarity of the solvent. On the one hand, in toluene, upon photoexcitation of the anthryl-ethynyl-aniline, the formation of a (1*)(SubPc) state is observed which decays into a (3*)(SubPc) manifold before deactivating to the ground state. On the other hand, increasing the polarity of the solvent to tetrahydrofuran and benzonitrile, significantly modifies the fate of the photoexcited state. In this new scenario, the (1*)(SubPc) state, formed directly upon 550 nm light stimulation or by 1*(anthryl-ethynyl-aniline) sensitization upon 405 nm excitation, transforms into a charge transfer (SubPc)(delta-)-anthryl-ethynyl-aniline(delta+) state which further evolves into a fully charge-separated (SubPc)(center dot-)-anthryl-ethynyl-aniline(center dot+) species before deactivating to the ground state.