Intramolecular fluorescence energy transfer in nitrobenzoxadiazole derivatives of polyene antibiotics

Spectroscopic properties of the polyene antibiotic Nystatin and its nitrobenzoxadiazole derivative have been characterized by lifetime and quantum yield measurements. The data suggest that Nystatin and other polyene antibiotics exhibit spectral features common to other linear polyenes such as diphenylhexatriene and parinaric acid, and support the conclusion that the strong absorption (εmax ~70 000 M−1 cm−1; λ = 306 nm) is due to a symmetry-allowed transition to a higher excited state while the red-shifted emission occurs from a lower lying excited state through a weak, symmetry-forbidden transition.Nitrobenzoxadiazole derivatives also exhibit efficient intramolecular fluorescence energy transfer from the polyene chromophore to the nitrobenzoxadiazole chromophore (λcm = 535 nm). The lifetime and quantum yield measurements suggest that the predominant mechanism of energy transfer is via a Dexter type transfer in a fraction of molecules with appropriate conformations.