Effect of solvent influence on J-aggregate of tetra-p-hydroxyphenylporphyrin (THPP) under different pH

In this paper, tetra-p-hydroxyphenylporphyrin (THPP) is dissolved in different solvents (chloroform, ethanol and N,N-dimethylformamide(DMF), Solvent effect is closely related to the nature and extent of solute–solvent interactions. Solvents have great influence on spectral characteristic and physicochemical processes of THPP. It is commonly acknowledged that solvent-dependent spectral shifts can arise from either general or specific solvent effects in the electronic transitions of solutes. For porphyrin, the solute–solvent interaction promotes conformational distortion of porphyrin plane in solution. Based on observed photophysical behavior in different polar solvent, the porphyrin can be grouped into “normal” and “perturbed” categories. The distortion of porphyrin plane causes redistribution of electron density, which changes the acid and basic properties of pyrrolic nitrogen atoms in the center of porphyrin ring. Furthermore, the solvent effects influence aggregate properties of porphyrin in solution. We confirm the results by the pH-titration experiment in the three solvent and investigate the difference of structure between J-aggregate and monomer by the Raman.