PHOTOPHYSICAL BEHAVIOUR OF NEW PYRROLOCOUMARIN DERIVATIVES

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Abstract
Abstract— The photophysical behaviour of new pyrrolocoumarins with different substituents on the nitrogen are reported. The photophysical properties of these pyrrolocoumarins are generally in agreement with those of the psoralens: a strong absorption (240–400 nm), a weak fluorescence (400–680 nm) characterized by a short singlet lifetime, and a rather strong phosphorescence at 77 K (480–600 nm). The absorption and fluorescence properties were investigated in several solvents. The shift of the fluorescence maximum is interpreted on the basis of the solvatochromic parameters π*, α and β. The triplet‐triplet absorption spectra also depend on the nature of the solvent, while the triplet excited state has a lifetime of a few microseconds at room temperature (concentration 2.5 × 10−4M). Some absorption and fluorescence characteristics of the 4′,5′‐dihydropyrrolocoumarins, which are suitable models for the 4′,5′‐monoadducts to pyrrolocoumarins are reported.