Fluorescence of carbonyl-containing intraionic polymethines

Area of Science:

• Organic Chemistry
• Photophysics
• Computational Chemistry

Background:

• Indole-based intraionic polymethines are a class of dyes with potential applications in various fields.
• The electronic structure and spectral-fluorescent properties of these dyes are influenced by their molecular structure, particularly the presence and position of carbonyl groups.
• Solvation effects can further modulate the photophysical behavior of these molecules.

Purpose of the Study:

• To investigate the electronic structure and spectral-fluorescent properties of four related indole-based intraionic polymethines.
• To understand how the position of carbonyl groups within the polymethine chromophore affects UV/Vis absorption and fluorescence spectra.
• To elucidate the influence of solvation on the fluorescence quantum yield of these dyes.

Main Methods:

• Experimental measurements of absorption and fluorescence spectra.
• Quantum chemical simulations using time-dependent density functional theory ((TD) DFT).
• Analysis of spectral data in conjunction with theoretical calculations.

Main Results:

• The position of carbonyl groups in the acceptor part of the molecule substantially affects the UV/Vis and fluorescence spectra.
• Solvation of carbonyl groups by electrophilic protic solvents can lead to either an increase or decrease in fluorescence quantum yield, or have no significant effect, depending on the specific dye structure.
• Observed spectral and fluorescence behaviors are consistent with (TD) DFT simulation results.

Conclusions:

• The carbonyl group's position is a critical determinant of spectral and fluorescence characteristics in these indole-based polymethines.
• Solvent-solute interactions, specifically solvation of carbonyls, play a complex role in modulating fluorescence quantum yield.
• A combination of experimental spectroscopy and (TD) DFT calculations provides valuable insights into the structure-property relationships of these dyes.