Light Induced Proton Coupled Charge Transfer Triggers Counterion Directional Translocation.

Area of Science:

• Photochemistry
• Supramolecular Chemistry
• Spectroscopy

Background:

• The BPym-OH dye molecule exhibits coupled excited-state intramolecular proton-transfer (ESIPT) and charge-transfer (CT) reactions, termed PCCT.
• Understanding light-induced ion motion in molecular systems is crucial for developing advanced optical materials.

Purpose of the Study:

• To demonstrate and visualize directed anion translocation along the BPym-OH dye molecule.
• To investigate the driving forces and temporal dynamics of coupled ESIPT and CT reactions.
• To correlate ion motion with fluorescence spectral shifts.

Main Methods:

• Steady-state and time-resolved spectroscopy.
• Computer simulation and modeling.
• Synthesis of the BPym-OH dye molecule.

Main Results:

• Directed translocation of perchlorate (ClO4-) anions from cationic to neutral sites on the BPym-OH molecule was observed.
• Excited-state charge redistribution, enhanced by ESIPT, provides a stronger driving force for ion motion than CT alone.
• A red-shifted fluorescence band (750 nm) associated with ion translocation appears at ~83 ps, distinct from the initial PCCT fluorescence (640 nm, <200 fs).

Conclusions:

• Fluorescence techniques can visualize light-triggered ion translocation and its driving force.
• The study successfully separates the temporal and energetic manifestations of ion motion and PCCT.
• This work offers insights into controlling and observing ultrafast ion dynamics in molecular systems.