Fluorescence of p-hydroxyazobenzocrowns - Tautomeric equilibrium effect

Area of Science:

• Photochemistry
• Organic Spectroscopy
• Supramolecular Chemistry

Background:

• Para-hydroxyazobenzocrowns are macrocyclic compounds with potential applications in sensing and molecular recognition.
• Understanding their spectroscopic properties is crucial for optimizing their function.
• Previous studies have not fully characterized their photophysical behavior or tautomeric equilibria.

Purpose of the Study:

• To investigate the spectroscopic properties of para-hydroxyazobenzocrowns, including novel compounds.
• To determine quantum yield (QY) values for this class of macrocycles.
• To analyze the influence of substituents and macroring size on spectral characteristics and tautomerism.

Main Methods:

• UV-Vis absorption and emission spectroscopy were employed.
• Nuclear Magnetic Resonance (¹H NMR) and Fourier-Transform Infrared (FTIR) spectroscopy were used for characterization.
• Theoretical calculations were performed to determine dipole moments and validate experimental findings.

Main Results:

• First-time reported quantum yield (QY) values for para-hydroxyazobenzocrowns range from 0.122 to 0.195.
• Highest QY values were observed in crowns with two phenyl substituents.
• Spectroscopic data revealed the impact of aromatic ring substituents and macroring size on spectral characteristics, considering the azophenol–quinone-hydrazone tautomeric equilibrium.

Conclusions:

• The study provides a comprehensive spectroscopic characterization of para-hydroxyazobenzocrowns.
• Quantum yield values and substituent effects offer insights into their photophysical behavior.
• Established alignment between experimental and theoretical results enhances understanding of these macrocycles.