Non-peripheral 4-acetamidophenol-substituted phthalocyanines of Co(II), Cu(II) and Ni(II): Synthesis, photodegradation and TD-DFT studies

Metallophthalocyanine complexes bearing four non-peripheral 4-acetamidophenol substituents were synthesized with Co(II), Cu(II) and Ni(II) metal centers and characterized by FT-IR, UV-Vis,1H-NMR and MALDI-TOF-MS techniques. The photostability of the complexes was evaluated experimentally in DMSO and further supported by computational studies. All complexes exhibited high photostability, with photodegradation quantum yields following the order CoPc-4 < CuPc-5 < NiPc-6. The obtained values are consistent with those reported for structurally related analogues. TD-DFT calculations suggest that this trend may be governed by the energy gap between the photoexcited Q-band state and the lowest accessible excited state, which narrows in the order CoPc-4 > CuPc-5 > NiPc-6 as a consequence of the d-electron configuration of the metal center and thus may influence how much absorbed energy is dissipated as heat before photodegradation can occur.