Electro-optical properties investigation of a series of hydroxylphenylporphyrins

A one-step method was used to synthesize five hydroxylphenylporphyrin monomers with different structures [R.G. Little, J. Heterocyclic Chem. 18 (1981) 129]. They were confirmed by means of different spectroscopic analysis methods. The effects of the number and the position of the peripheral hydroxylphenyl groups of the porphyrin ring and solvents on their fluorescence spectra were discussed according to the change of the UV spectra. It was found that the fluorescence intensity was enhanced with an increase in the number of the peripheral hydroxylphenyl groups of the porphyrin ring. It was also found that the fluorescence intensity at 430 nm was very weak for tetrahydroxylphenylporphyrin (TPP) and tetraphenylporphyrin (5). This phenomenon is related to the structural symmetry. The red shift of the fluorescence spectra in polar solvent DMF relative to that in CH2Cl2 can be explained on the basis of the effect of solvation. The fluorescence intensity of hydroxylphenylporphyrin 2 in DMF at 430 nm is much stronger than that in CH2Cl2. The surface photovoltaic property of TPP and hydroxylphenylporphyrins 1–5 was studied by means of surface photovoltage spectra (SPS) and field induced surface photovoltage spectra (FISPS), which reveals that all the hydroxylphenylporphyrin are P-type semiconductors. The SPV spectral bands of all the hydroxylphenylporphyrins correspond to the π → π* transition. The SPS was similar to the UV–Vis spectra. It has also been found that the stronger the fluorescence intensity is, the weaker the surface photovoltage intensity is. For all the hydroxylphenylporphyrins and TPP, the surface photovoltage (SPV) of TPP is the weakest, that of hydroxylphenylporphyrin 1 is the strongest, then the SPV of the other hydroxylphenylporphyrins are gradually weakened with an increase in the number of the peripheral hydroxylphenyl groups of the porphyrin ring. This result indicates that controlling the number and position of the peripheral hydroxylphenyl substituting groups of the porphyrin ring and using different solvents could obtain the porphyrins with different electro-optical properties.