Theoretical investigation of the structural and spectroscopic properties of expanded metalloporphyrin complexes

The frontier molecular orbitals, UV–Vis absorption spectra, charge transfer (CT) and triplet excited states of 12 expanded D–A porphyrin/benzoporphyrin complexes were investigated using the density functional theory (DFT) method and time-dependent DFT in this work. The results showed that thiophene was an effective fragment for absorption of ‘long wavelength’, while the benzoporphyrin worked on the ‘short wavelength’, which was derived from its saddle-shaped structure; this expanded D–A conjugated system had a mild CT process with anthraquinone/isoindigo as acceptors and a strong CT process with naphtoquinone as acceptor. In addition, based on the simulation of the triplet state, the theoretical phosphorescence wavelength range of this series of derivatives was between 1000 and 1200 nm. This study is expected to assist the design of conjugated porphyrin for the field of porphyrin chemistry.