Functionalized porphyrins and other tetrapyrrole derivatives are of great importance in biological, chemical, and optical systems because of their unique physicochemical and optoelectronic properties. Nitro substituted porphyrinoids have been investigated extensively for their redox catalytic activity, nonlinear optical materials, theranostics, and in artificial solar energy harvesting devices. We present here the photophysical properties of a series of nitro porphyrinoids in polar (DMSO) and non polar (toluene) solvents. The nitro group on the porphyrins acts as precursor for the amino group formation also reported to decrease the fluorescence quantum yield and the amount of quenching depends on the number and position of the nitro groups. The low fluorescence quantum yield is complementary of their high triplet quantum yield, makes them to use as a good platform to generate new generation photosensitizer for photodynamic therapy. Nitro groups drastically affect the electronic properties of the Porphyrins when attached to the β-pyrrole position and can interact with a nearby bulky meso substituent to significantly distort the macrocycle. There are two fluorescence life times for each studied nitro porphyrinoid both under ambient conditions as well as under inert N2 atmosphere, which corresponds to distinct molecular structure, may be tautomers, atropisomers or some kind of confirmers. We propose that molecular distortion due to steric hindrance is the prevailing cause behind all of the unusual photophysics.

Photophysical studies of nitro substituted porphyrinoids

253rd National Meeting (2017)

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