Spectral characteristics of fluorescence probes based on pyrene in solution and in polymer matrix

Abstract

Spectral properties of four types of bifunctional probes based on pyrene and sterically hindered amines (HAS) were compared in solution of cyclohexane and methanol and in polymer matrices as isotactic polypropylene (iPP), polystyrene (PS), poly(methyl methacrylate) (PMMA) and poly(vinyl chloride) (PVC). Absorption spectra of these probes strongly depend on the type of linkage. When the carbonyl group in the linkage is in α-position to pyrene ring, the absorption bands are broader with rather poor vibrational resolution. The carbonyl group in α-position influences the emission spectra as well. For derivatives of 4-oxo-4-(1-pyrene)butanoic acid (I), the broad emission band was observed. Some vibrational resolution was observed for probes based on 1-pyrenecarboxylic acid (IV). Lifetime of these probes is in the range 1–10 ns. When methylene group instead of carbonyl is attached to pyrene and forms the link, the absorption spectra are the same as that of alkyl-substituted pyrene. This behaviour was shown for derivatives of 1-pyreneacetic acid (III) and 4-(1-pyrene)butyric acid (II). The emission spectra of these probes are similar as parent alkyl pyrene. The lifetime is in the range above 100 ns. The influence of solvent polarity and polymer matrix on spectra was not very pronounced for probe of parent amine types Ic–IVc. The decay of fluorescence of probes of this type was satisfactorily fitted to monoexponential function. The efficiency of intramolecular quenching observed for oxidised probes Id–IVd is in the range from about 1.5 for derivative Id to value of about 10 for IIId. It was influenced by type of linkage and medium. The decay of fluorescence of linked pyrene chromophore of probes Id–IVd is better fitted by biexponential function.