Asymmetric Antipodal β-Functionalized Push-Pull Porphyrins Based on β,β'-Fused Imidazole Rings: Synthesis, DFT,...

A new series of asymmetric β-functionalized push-pull porphyrins with a π-extended electron system is reported. The synthetic strategy enables the selective introduction of two distinct moieties into the porphyrin core, and the asymmetric β-functionalization induces unique electronic perturbations, resulting in push-pull systems with enhanced optical properties. The UV-vis spectra exhibit broad absorption bands with high FWHM values (30-55 nm), while the fluorescence quenching in polar solvents suggests a possible deactivation of the porphyrins' excited state by an electron-transfer process from the donor (diphenylammino) to the acceptor (nitro) group. The nature of the electron-transfer can find its origin in the charge-transfer character of the electronic transitions, as evidenced by DFT studies. ¹H NMR investigations reveal a self-assembly tendency for ZnP-3, likely due to its high dipole moment (11.4 D). Additionally, upon titration, the labile proton on the imidazole ring leads to the formation of a distinct absorption band in the visible region (660-680 nm), indicative of base-responsive behavior. The capability of singlet oxygen generation was verified for porphyrins 5a and H₂P-2, in both neutral and anionic forms. The synthetic approach developed unlocks access to a broad array of functionalized organic materials previously unattainable, with potential applications in photovoltaics, nonlinear optics, and photodynamic therapy.