Ultrafast time-resolved fluorescence spectroscopy of novel ketocyanine dyes

Abstract

Using ultrafast time-resolved fluorescence spectroscopy, the fluorescent characteristics of two ketocyanine dyes—2,5-di[(E)-1-(4-diethylaminophenyl)methylidene]-1-cyclopentanone (CPET) and 2,5-di⨑ub;(E)-1-[4-(4,7,10,13-tetraoxa-1-azacyclopentadecyl)phenyl] ???methylidene⫂ub;-1-cyclopentanone (CPCR)—are studied in organic solvents and in membranes of human erythrocyte ghosts. The position of the fluorescence spectrum of each probe depends strongly on the polarity of the environment due to a considerable change in the dipole moment of the probe after its excitation. An inhomogeneous broadening of the electronic spectra of both dyes is observed, which manifests itself in the bathochromic shift of the fluorescence spectrum upon displacement of the excitation frequency toward the red edge of the absorption spectrum, as well as in the dependence of the shape of the excitation spectrum on the frequency of recording. The lifetime of the excited state of the probes increases with increasing polarity or viscosity of the environment. Analysis of the instantaneous emission spectrum of CPET and of its fluorescence decay time distribution in human erythrocyte ghosts shows that there are two types of binding sites of the probe to the lipid membrane.