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

Abstract

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 = Pî, Z = 2, a (Å) = 8.4849(1); b (Å) = 12.0292(2); c (Å) = 12.9601(2); α(°) = 95.580(1); β(°) = 93.170(1); γ (°) = 99.942(1)) and 6b, crystallized in monoclinic system (Space group = P21/n, Z = 4, a (Å) = 3.9282(6); b (Å) = 32.274(1); c (Å) = 27.440(2); β(°) = 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.