Syntheses and photophysical properties of diaminotetraphenylporphyrins and their corresponding polyimides

Abstract

Two free base porphyrins, 5,10-bis(4-aminophenyl)-15,20-diphenylporphyrin (cis-DATPP), 5,15-bis(4-aminophenyl)-10,20-diphenylporphyrin (trans-DATPP), and their zinc metalated analogues (cis-ZnDATPP and trans-ZnDATPP) were synthesized. A series of their corresponding polyimides were obtained by the condensed polymerization of the respective monomeric isomer DATPP with a 1:1 ratio of 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (PFMB) and 4,4′-hexafluoroisopropylidenediphthalic anhydride (6FDA). The inclusion of PFMB and 6FDA into the polymeric backbone causes the polymers to be moderately to highly soluble in organic polar solvents. The molar content of the respective DATPP monomer varied between 5 and 30%. All compounds were structurally characterized by 1H NMR and ATR-IR spectroscopy and the porphyrin content in the polyimides was determined by UV–Visible absorption spectroscopy. Photophysical properties consisted of measuring both the UV–Visible (ground state) absorption and fluorescence (excited state) spectra, fluorescence quantum yields (Φf), and fluorescence lifetimes (τf) in dichloromethane and N,N-dimethylacetamide. Fluorescence quenching was also measured and observed by the Stern-Volmer relationship, using 9,10-anthraquinone (AQ) as the quencher molecule. Both the bimolecular rate constant of fluorescence quenching (kq) and the Stern-Volmer constant (KQ) were calculated from this relationship. Furthermore, deviations from linearity depicted in the Stern-Volmer plots for TPP and ZnTPP at higher concentrations of AQ were also measured as a means of examining and explaining the simultaneous occurrence of dynamic (collisional) quenching and static quenching in the mechanisms of fluorescence quenching. It was found in this work that the significantly larger values in the static quenching constant (KS) than in the dynamic quenching constant (KD) are indicative that static quenching and ground state complex formation between the fluorophore and quencher is the dominant mechanism of fluorescence quenching of these systems at higher quencher concentrations.