Arresting Tautomerization in a Single Molecule by the Surrounding Polymer: 2,7,12,17-Tetraphenyl Porphycene

Abstract

2,7,12,17-Tetraphenyl porphycene (TPPo) is known to undergo ultrafast (<1 ps) double-hydrogen transfer in solution. Fluorescence studies of single TPPo molecules embedded in a polymer matrix and excited with an azimuthally polarized laser beam reveal, for a considerable fraction of the population, double-lobe spatial emission patterns attributed to the absence of tautomerism. In consecutive image scans, these patterns change their orientation to nearly orthogonal. In some cases, switching of the orientation direction occurs through an intermediate case with a doughnut-shaped pattern, indicating the presence of fast tautomerism. These findings demonstrate that local polymer environment can drastically change the thermodynamics or kinetics of tautomerization. They also point out the contribution of the motion of peripheral substituents in the hydrogen-transfer coordinate. TPPo is proposed as a good probe for studying relaxation dynamics in thin polymer films.