GROUND AND EXCITED STATE DIPOLE MOMENTS OF ELONGATED P-AMINOBENZOICACID ANALOGUE, 4-((4)DIAZENYL)BENZOIC ACID, FROM SOLVATOCHROMIC ANALYSES BY MODIFIED SOLVATOCHROMIC EQUATIONS

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.