Asymmetric Antipodal β-Functionalized Push–Pull Porphyrins Based on β,β′-Fused Imidazole Rings: Synthesis, DFT, Photophysical Studies, and the Base-Dependent Equilibrium Characterization in Nonaqueous Solutions

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.