Density functional theory characterisation of 4-hydroxyazobenzene.

Area of Science:

• Computational chemistry
• Molecular modeling
• Spectroscopy

Background:

• 4-hydroxyazobenzene is an important organic compound with potential applications.
• Understanding its structural and electronic properties is crucial for its use.
• Computational methods offer a way to study these properties without experimental limitations.

Purpose of the Study:

• To investigate the structural properties, vibrational spectra (IR and Raman), dipole moment, polarisability, hardness, and chemical potential of trans and cis 4-hydroxyazobenzene.
• To compare the stability and electronic characteristics of the two isomers.
• To identify spectroscopic signatures for distinguishing between the trans and cis configurations.

Main Methods:

• Density Functional Theory (DFT) calculations using B3LYP functionals.
• Employment of various basis sets including 6-31G, 6-31++G, 6-31G(d,p), 6-31++G(d,p), 6-31G(2d,2p), 6-31++G(2d,2p), and 6-311++G(2d,2p).
• Validation of basis set performance and exploration of exchange-correlation functionals (SVWN, PW91).

Main Results:

• Optimized planar structures for trans configurations and asymmetric structural parameters in both isomers due to the hydroxyl group.
• Identification of two specific IR or Raman active frequencies capable of differentiating between trans and cis configurations.
• The trans configuration was found to be more stable than the cis configuration by 67 +/- 2 kJ mol(-1) at 0 K.
• The dipole moment difference between trans and cis 4-hydroxyazobenzene is smaller compared to azobenzene.

Conclusions:

• The study provides a comprehensive computational analysis of 4-hydroxyazobenzene's isomers.
• Distinct spectroscopic markers (IR/Raman frequencies) are proposed for isomer identification.
• The trans isomer exhibits greater thermodynamic stability, influencing potential applications.