First observation of spectral fluctuation in a single molecule of a rigid-rod π-conjugated polymer

The photonic function of the light-emission from a rigid-rod conjugated polymer, poly(9,10-anthracenediyl-ethynylene-1,4-phenylene-ethynylene) [poly(AEPE)], was measured using total internal reflection fluorescence microscopy (TIRFM), which is a single molecule detection technique that is carried out in methanol at room temperature. The light-emission from a single polymer molecule as it slowly and dynamically changes over a cycle lasting a few seconds has been successfully detected using TIRFM with a built-in spectroscope. Special mention must be made of the fact that we were able to observe for the first time fluctuations in the wavelength of the emission spectra resulting from structural changes in a single polymer molecule. Although poly(AEPE) had a rigid-rod main chain, these changes occurred very slowly over a time-scale of several seconds at room temperature. Thus, single molecule spectroscopy appears to be a powerful tool for studying the dynamic behavior of single macromolecules.