Photothermally induced conformational changes in poly(substituted thiophene) film leading to nanometer surface protrusion: A near-field fluorescence microspectroscopic study

The relationship between changes of fluorescence spectrum, polymer conformation, and surface morphology of a poly{3-[2-(N-dodecylcarbamoyloxy)ethyl]thiophene- 2,5-diyl} (P3DDUT) film were examined by near-field fluorescence microspectroscopy. By a 488 nm excitation using the near-field probe, a nanometer scale protuberance was formed on the surface. The excitation also induced a blue shift in the fluorescence spectrum. By analyzing the spectral change, it was confirmed that photothermally induced conformational changes (rod-coil transformations) lead to the nanometer surface protrusion. Moreover, in exposure time dependence measurements, it was found a time lag in appearances of the blue shift and the protrusion, indicating that an accumulation of transformed polymers is necessary to evolve into the surface protrusion.