Tailoring the band-gap, optical and fluorescent properties of 3,5-diamino-benzoic acid via functionalization with chemical groups: A DFT study

3,5-diaminobenzoic acid (3,5-DABA) with chemical formula C7H8N2O2 was functionalized with CH3-, OH-, NH2and NO2- to obtain: CH3-3,5 DABA, OH-3,5 DABA, NH2-3,5DABA and NO2-3,5DABA. These molecules were built with Gauss view 6.0 and their structural, spectroscopic, optoelectronic and molecular properties were investigated using density functional theory (DFT). B3LYP (Becke's 3-parameter exchange functional with Lee-YangParr correlation energy) functional and 6-311+ G (d, p) basis set were used to understand their reactivity, stability and optical activity. Integral equation formalism polarizable continuum model (IEF - PCM) was used to calculate the absorption wavelength, energy required to excite the molecules and oscillator strength. Our results reveal that the functionalization of 3,5 DABA with the groups caused a decrease of the energy gap from 0.1563 eV, to 0.1461 eV, 0.13818 eV and 0.13811 eV in NO2-3,5DABA, OH-3,5DABA and NH2-3,5DABA respectively. The lowest energy gap of 0.13811 eV for NH2-3,5DABA is in good agreement with its highest reactivity value (global softness of 7.240). The most observed significant donor - acceptor NBO interactions where found to occur between *& pi;C16-O17 & RARR; *& pi;C1-C2, *& pi;C3-C4 & RARR; *& pi;C1-C2, *& pi;C1-C2 & RARR; *& pi;C5-C6, *& pi;C3-C4 & RARR; *& pi;C5-C6, *& pi;C2-C3 & RARR;*& pi;C4-C5 natural bond orbitals having second- order stabilization energies of 101.95 kcal/mol, 368.41 kcal/ mol, 174.51 kcal/mol, 255.63 kcal/mol and 235.92 kcal/mol in 3,5-DABA, CH3-3,5-DABA, OH-3,5-DABA, NH23,5-DABA and NO2-3,5-DABA respectively. The highest perturbation energy was observed in CH3-3,5DABA while the lowest perturbation energy was observed in 3,5DABA. The absorption band of the compounds were observed in the order: NH2-3,5DABA (404 nm) > N02-3,5DABA (393 nm) > OH-3,5DABA (386 nm) > 3,5DABA (349 nm) > CH3-3,5DABA (347 nm).