Time-Resolved Fluorescence Measurements on Poly(ethylene naphthalene-2,6-dicarboxylate)

Abstract

The time-resolved fluorescence behavior of poly(ethylene naphthalene-2,6-dicarboxylate) (PEN) has been investigated by synchrotron radiation. Solutions of different concentrations of PEN dissolved in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) (10-4 and 10-2 M) have been excited at a wavelength of 340 nm, and the emission has been monitored in the wavelength range from 360 to 480 nm in 10 nm steps. The measurements have been performed at two different temperatures (288 and 298 K). Nearly all decay curves can be fitted by a sum of three exponential functions. These three exponential decay time components seem to be parameters which give the main values of a distribution of decay times. We obtained such distribution functions by assuming a simple model on the basis of excitation energy migration from monomer units (donors) to excimer sites (traps) by a Förster type mechanism. These distribution functions can be fitted by a sum of three exponential functions with reliable confidence parameters. The fits on the calculated distribution functions are in good agreement with the fits obtained from the measured data. We compared these results with data obtained on amorphous PEN films excited at the same energy. Again three exponential functions are needed to fit the measured data. The measured fluorescence decay curves can also be explained by our model.