Designing free-base phenylcorroles to absorb in the phototherapeutic window.

Molecules used as photosensitizers in photodynamic therapy are required to satisfy several criteria for optimal performance. Among these, intense light absorption in the phototherapeutic window (650-950 nm) is highly desirable. Density functional theory QM/MM calculations were used to study the absorption spectra of a sample of free-base phenylcorroles in methanol. The distinctive structural parameters of the subset of phenylcorrole molecules in the sample, with absorption peaks in the phototherapeutic window, were identified. One of these structural parameters was exploited by introducing suitable atomic substitutions into the phenylcorrole, which resulted in red shifts (and blue shifts) in the lowest energy absorption peaks, with some of them occurring within the phototherapeutic window. These red shifts are shown to be related to the degree of variation of the structural parameter and to the atomic substitutions. These results show a strategy to design free base corroles that absorb within the phototherapeutic window.