Synthesis, crystal structure, Hirshfeld surface analysis, density function theory calculations and photophysical properties of methyl 4′-[(4-bromobenzoyl)oxy]biphenyl-4-carboxylate: a compound with bromine...oxygen contacts

In the mol-ecular title compound, C₂₁H₁₅BrO₄, the dihedral angles between the aromatic bromo-benzene ring and the immediate neighbors (first and second aromatic ring of the biphenyl moiety) are 56.57 (2) and 50.91 (4)°. The dihedral angle between the aromatic rings of the biphenyl fragment is 5.78 (4)°. The torsion angles across the ester groups associated with bromo-benzene and methyl moieties are 178.0 (1) and 176.86 (2)°, respectively, revealing an <i>anti</i>-periplanar conformation in both cases. In the crystal, the packing of the mol-ecules is stabilized by Br⋯O contacts running infinitely along [001]. In addition, the crystal packing is consolidated by various C-H⋯π inter-actions. Hirshfeld surface analysis revealed that the most important contributions to the crystal packing arise from H⋯H (27.1%), C⋯H/H⋯C (39.3%), O⋯H/H⋯O (15.4%) and Br⋯H/H⋯Br (10.6%) contacts. The net inter-action energies for the title compound were computed as <i>E</i> _ele = -41.9 kJ mol^-1, <i>E</i> _pol = -11 kJ mol^-1, <i>E</i> _dis = -209.7 kJ mol^-1 and <i>E</i> _rep = 108.9 kJ mol^-1, with a total inter-action energy <i>E</i> _tot of -167.9 kJ mol^-1. The ground-state dipole moment (μ_g) is calculated as 1.2936 debye and the energy gap between HOMO and LUMO orbitals is 4.5203 eV as calculated with density functional theory using the B3LYP/6-31 G level basis set. The electronic absorption and fluorescence spectra of the compound were recorded and studied in different solvents by varying polarity. These results were used to elucidate the solvatochromic properties, and spectral deviations were studied by the linear solvation energy relationship. Lippert, Bakhshiev, and Bilot-Kawski-Chamma-Viallet equations were used to estimate the ground and excited-state dipole moments (μ_e). The excited dipole moment is found to be higher than the ground state dipole moment, which indicates that π-electrons are more distributed in polar excited mol-ecules.