Optical imaging of excited-state tautomerization in single molecules

Abstract

Tautomerism process of single fluorescent molecules was studied by means of confocal microscopy in combination with azimuthally or radially polarized laser beams. During a tautomerism process the transition dipole moment (TDM) of a molecule changes its orientation which can be visualized by the fluorescence excitation image of the molecule. We present experimental and theoretical studies of two porphyrazine-type molecules and one type of porphyrin molecule: a symmetrically substituted metal-free phthalocyanine and porphyrin, and nonsymmetrically substituted porphyrazine. In the case of phthalocyanine the fluorescence excitation patterns show that the angle between the transition dipole moments of the two tautomeric forms is near 90°, in agreement with quantum chemical calculations. For porphyrazine we find that the orientation change of the TDM is less than 60° or larger than 120°, as theoretically predicted. Most of the porphyrin molecules show no photoinduced tautomerization, while for 7% of the total number of investigated molecules we observed excitation patterns of two different trans forms of the same single molecule. We demonstrate for the first time that a molecule, undergoing a tautomerism process stays in one tautomeric trans conformation during a time comparable with the acquisition time of one excitation pattern. This allowed us to visualize the existence of each of the two trans forms of one single porphyrin molecule, as well as the sudden switching between these tautomers.

Detection of charge dynamics of a tetraphenylporphyrin particle using GaAs-based nanowire enhanced by particle–metal tip capacitive coupling

“…3(a), was 20 nm from the nanowire surface. This height of the particle corresponded to the stack of twenty TPP molecules, which was estimated from the π-π intermolecular distance 28) and the thickness of the TPP molecule 29) , assuming that planar-shaped TPP molecules were stacked on the nanowire in parallel to the surface plane 30) .…”

The Role of Molecular Dipole Orientation in Single‐Molecule Fluorescence Microscopy and Implications for Super‐Resolution Imaging

“…[19] A further twist on such approaches can be realized by exciting the molecule with azimuthally or radially polarized doughnut modes. [20] Due to the scanning nature of all these techniques they are not well suited for detecting many molecules in parallel, which makes them non-ideal for incorporation into single-molecule super-resolution imaging (see Section 2).…”

Real-time fluorescence visualization of slow tautomerization of single free-base phthalocyanines under ambient conditions

“…10 This suggests a much slower rate of tautomerization for isolated H 2 Pc molecules. However, an early attempt to use fluorescence microscopy to visualize the ETDMs of single H 2 Pcs embedded into polymers or attached to silica failed, 17 presumably because of the low rate of image acquisition (B100 s) compared with the rate of tautomerization. In this study, we report the real-time visualization of the ETDMs of single H 2 Pcs using defocused wide-field microscopy at a temporal resolution of 100 ms. [18][19][20][21][22][23] We found that a H 2 Pc derivative shows slow tautomerization at an air/octadecyl-group-modified glass interface, which is consistent with previous DFT calculations.…”