Synthesis and spectroscopic analysis of benzylidene imidazolone linked to P-porphyrins through axial ligand

Abstract

Tetraphenylporphyrinatophosphorus(V) complexes (1) comprising two axially linked benzylidene imidazolone (Biz) moieties, which are chromophores of the green fluorescent protein, were prepared. In medical applications such as photodynamic therapy, the P-porphyrin part (Ptp) is expected to sensitize to generate singlet oxygen, whereas the Biz units act as fluorescent probes. The fluorescence spectra of 1 were analyzed under the excitations of Biz at 370 nm. Fluorescence stemming from the excited states of Biz and Ptp was observed at 460 and 610 nm, respectively. The intramolecular quenching of Biz in the excited singlet state by Ptp occurred, resulting in weak fluorescence from Biz. The introduction of a cyano group in the Biz units of 1 enhanced their fluorescence quantum yield up to 7.7 × 10⁻⁴. The fluorescence spectra of 1 under the excitations of Ptp at 550 nm were extremely similar to that of a reference compound of P-porphyrin without the Biz chromophore, dimethoxy(tetraphenylporphyrinato)phosphorus chloride. The physicochemical parameters of Ptp remained unaltered following the introduction of Biz on the axial positions of P-porphyrin.