The title compound, C20H18O4 (I), was synthesized by O-acylation of 6-hydroxycoumarin with 4-tert-butylbenzoyl chloride. The compound was characterized with ESI-MS, FT-IR, 1H and 13C NMR spectroscopic analysis. Furthermore the single crystal X-ray structure obtained has C2/c space group and crystallizes in the monoclinic system with dimensions of 𝑎 = 36.7355 (4) Å , 𝑏 = 6.8375 (1) Å , and 𝑐 = 13.6203 (2) Å . In the structure, the planar coumarin ring system and the benzene ring of the benzoate group are almost perpendicular, forming a dihedral angle of 87.22 (8)°.
These moieties are linked by the exocyclic ester (-COO-) fragment making a torsion angle of 66.0°. The molecules are associated via C—H•••O interactions to form R22(24) dimers which arrange the coumarin moiety into layers nearly parallel to the (20 ) plane. Likewise, the crystal structure is supported by C–H•••π and π–π interactions between neighboring rings with centroid–centroid distances less than 3.8 Å . Also, the DFT method was used to minimize the title compound and assess its HOMO and LUMO electron density plots, as well as its molecular electrostatic potentials. Additionally, the HOMO-LUMO energy gap and non-linear optical (NLO) effects were calculated to better understand the molecule's properties. These
calculations yield dipole moment, HOMO–LUMO energy gap, polarizability and first-order hyperpolarizability values of 7.71 D, 4.45 eV, 39.2x10-24 and 5.37x10-30 esu, respectively and are compared with those of the urea molecule for the assessment of NLO properties, as well as with the related coumarin derivative 2-oxo-2H-chromen-6-yl-4-methoxybenzoate (II).

6-Substituted coumarin derivative, Spectroscopic analysis, Conformational analysis