The molecular electronic properties of a novel tetraphenylporphyrin derivative †

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Abstract
The Langmuir properties of a novel tetraphenylporphyrin derivative based on tetra(4-aminosulphonyl)phenylporphyrin have been investigated. Porphyrin materials are of interest since they can readily exist in two electronic states, which can be characterized by their optical absorption spectra. These correspond to an uncharged free base species showing a main absorption band (Soret band) near 415 nm and a positively charged dication species with a shifted Soret band near 440 nm. Thew switching between these two states can be achieved by the addition or removal of two protons into or from the central porphyrin ring system. Recently, we have identified an additional state in which the Soret band lies at 490 nm and can be observed for porphyrin molecules existing in the form of a floating Langmuir layer at the air-water interface.