Abstract: UV and FTIR spectroscopic studies containing 0.01 and 0.001m solute Chlorochromones with electron donating and withdrawing groups) were done in 10 - 90% (w/w) methanol (ME) in DMSO/DMF solvent mixtures at room temperature The λmax of solutes vary with the % of ME. The decrease in λmax of all solutes was more in ME + DMSO than in ME + DMF. The amount of blue shift (lower wave length) has been used as a measure to the strength of hydrogen bond. Absence of n →* excitation in solute + ME + DMSO/ DMF was ascribed due to hydrogen bond formation. An irregular trends in OH,C=O ,S=O, C-Cl ,C-H ,NH etc. with increase of ME in solution at a particular concentration of solute indicated structure of the medium changed with ME content. In certain compositions of 0.01 and 0.01m, no changes in vibration frequencies were detected. Hydrogen bond formation of ME with carbonyl of, CL1 and CL2 was well supported by shifting of normal C=O to 1650 -1640 cm-1.In the case of 0.01m CL1, there was an initial increase in OH  50%ME. Further addition of ME in the system dropped it. Dilute solute concentration (i.e. 0.001m) did not show much appreciable change for this frequency upto 40%ME, while further addition of ME decreased the same. The magnitude of S=O remain unchanged after 10% ME for both 0.001 and 0.01m solute concentrations. The C-Cl was around 700 cm-1 in 20 - 80%ME. These results demonstrate the presence of strong interactions among the molecules of the solvent as well as between solute and solvent. Geometry optimizations of heterocyclic compounds, pure solvents and their 1:1 and 1:1:1 complex were carried out using the DFT/B3LYP method with medium size 6-31G (d) basis set available in G03(W) series of programs All optimized geometries were viewed through Gauss View 4.1 software to know exact nature of intermolecular interaction.

Keywords: Chalcones, Chlorochromones UV, FTIR, DFT and molecular interaction.

| DOI: 10.17148/IARJSET.2021.8618