研究目的
Investigating the low-temperature effect on the electronic structure and spectral-fluorescent properties of highly dipolar merocyanines.
研究成果
The absorption and fluorescence bands of negatively solvatochromic merocyanines are shifted hypsochromically upon freezing of their ethanol solutions to 77 K. This distinguishes them from both positively solvatochromic merocyanines and negatively solvatochromic ionic polymethines. The contribution of the dipolar polyene structure A3 to their electronic structure noticeably increases at low temperature in both the ground state S0 and excited state S1 due to the higher polarity of frozen ethanol and ordering of the solvate shell in the charge field of a dye.
研究不足
The PCM approach does not take into account strong specific solute-solvent interactions and is therefore unable to properly represent solvent effects in many cases. The solubility of polymethine dyes decreases and their tendency to form intermolecular associates/aggregates increases at low temperatures.
1：Experimental Design and Method Selection:
Absorption and fluorescence spectra of merocyanines were studied in frozen ethanol solutions at 77 K. The spectral bands were analyzed by the method of moments and deconvolution into Gaussian components.
2：Sample Selection and Data Sources:
A vinylogous series of reversely solvatochromic merocyanines based on benzimidazole and malononitrile were used.
3：List of Experimental Equipment and Materials:
Cary-500 spectrophotometer for absorption spectra, a large-aperture setup for fluorescence spectra, glass cuvette with a long protuberance immersed in liquid nitrogen.
4：Experimental Procedures and Operational Workflow:
The absorption and fluorescence spectra were recorded in ethanol solutions at 293 K and 77 K. The fluorescence intensity was corrected by the sensitivity of the equipment used.
5：Data Analysis Methods:
The spectral bands were analyzed by the method of moments, and the bandwidths were characterized as the deviation of a spectral band from its gravity center. The absorption and fluorescence bands were also analyzed using their deconvolution into Gaussian components.
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