Investigations of Donor-Acceptor Interactions in 1,3,5-Tris-(3-Methoxy & 3-Methyl Carboxy) Phenyl Ethynyl Benzene Derivatives Using Experimental and DFT Study

Two new 1,3,5-tris-(3-methoxy (6a) & 3-methyl carboxy (6b)) phenyl ethynyl benzene derivatives were synthesized from 1,3,5-triethynylbenze and 3-bromo anisole/methyl-3-bromo benzoate, respectively, under Sonogashira cross-coupling reaction conditions. The molecular structures of these two compounds were confirmed by spectral, CHN, and single-crystal XRD analysis. The compound 6a, crystallized in triclinic system (Space group = Pi, Z = 2, a (angstrom) = 8.4849(1); b (angstrom) = 12.0292(2); c (angstrom) = 12.9601(2); alpha(degrees) = 95.580(1); beta(degrees) = 93.170(1); gamma (degrees) = 99.942(1)) and 6b, crystallized in monoclinic system (Space group = P2(1)/n, Z = 4, a (angstrom) = 3.9282(6); b (angstrom) = 32.274(1); c (angstrom) = 27.440(2); beta(degrees) = 92.29(1)). Furthermore, the optimized molecular geometries were compared with experimental counter parts employing DFT approach. The complete spectroscopic studies of the titled compounds were carried out using analytical techniques, such as FT-IR, NMR, CV, and UV-VIS analysis and compared with the theoretical results. The first order hyper-polarizability, natural bond orbital analysis, frontier molecular orbitals, and molecular electrostatic potentials were performed on 6a&b, by employing the DFT method and compared with their ortho- and para-substituent compounds. These results indicated that the two compounds 6a&b, showed different donor-acceptor (D-A) interactions based on donor (-OCH3) or acceptor (-COOCH3) moieties attached to the benzene ring.