Schiff base bridged biporphyrin: Synthesis, characterization and spectral properties

Chromophoric molecules with mono-aminophenyl, 5-aminophenyl-10, 15, 20-triphenyl porphyrin, were chemically reduced from the precursors of 5-nitrophenyl-10, 15, 20-triphenyl porphyrin. The titled Schiff base bridged biporphyrins were furthermore prepared by condensation of 5-aminophenyl-10, 15, 20-triphenyl porphyrin with terephthalaldehyde. This novel conjugated Schiff base biporphyrin was well characterized by spectral determinations. Experimental results indicated that the titled compound possessed fluorescence enhancement in near infrared region. Compared with tetraphenyl porphyrin, both ultraviolet–visible absorption and fluorescence spectra of the titled compound appeared with slightly red shift. Photo experiments revealed that, after violet irradiation, the color of a chloroform solution with the titled compound changed sharply from pale green to dark green along with sensitively spectral variation during ultraviolet–visible absorption and electron paramagnetic resonance determinations. This sensitively photochromic mechanism was well explained by molecular recognition of the titled compound towards hydrogen chloride from the decomposition of the chloroform solvent. The titled compound was sensitive in recognizing towards hydrogen chloride.