Abstract:
n the present study, 4-((4-aminophenyl)diazenyl)benzoic acid (4-APDBA) has been synthesized
via electrophilic aromatic substitution of activated benzene derivatives through diazonium
electrophiles by self-coupling of para-aminobenzoic acid (PABA) and characterized by UV–
Visible and Fourier transform infrared (FTIR) spectroscopy. The absorption and fluorescence
spectra of PABA and 4-APDBA have been assessed in a series of organic solvents. In the
modified solvatochromic equation the tricky of inferring the Onsager radius of an elongated
molecule is studied from the point of view of solvent cavity volume. The equation recovers
structural dependency by including the real size and shape of compound of interest. The ground
(μg) and excited state (μe) dipole moments are determined by means of the improved LippertMataga,
Bakhshiev’s, Bilot-Kawski and McRae’s equations based on the solvent polarity
parameters. The ground-sate dipole moment determined using the improved Lippert’s-Mataga
equation remarkably yields quite close result with a values estimated with integral equation
formalism polarizable continuum model (IEF-PCM) with density functional theory (at B3LYP/6-
31G+(d,p) basis set level) methods. Higher values of dipolemoment have been observed for
excited state compared to the corresponding ground state values indicating an intramolecular
charge-transfer (ICT) and substantial redistribution of the π-electron density in more polar
excited state. The ground state dipole moment calculated with Lippert-Mataga for PABA (3.39 D) is fairly accurate to stark splitting experiment (3.3 D) and the of 4-APDBA (6.25 D)
approximate to the density functional theory calculation, 7.041 D, while this value with normal
equation is 4.18 D and 8.51 D for PABA and 4-APDBA respectively, which are large compared
with the modified equation and with accurate experimental result for PABA although
approximate to the theoretical value from this result the normal equation overestimate the
dipolemoment value compared with the improved equation therefore the modification is valid.
