Molecular structure analysis of 4-fluoro phenyl(4-methyl piperidin-1-yl) methanone and a comparative study of its optical, antimicrobial and antioxidant activities with 4-chloro phenyl (4-methyl piperidin-1-yl) methanone

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A new fluoro derivative of 4-methyl piperidine (FPMPM) was synthesized by Scholten-Baumann condensation reaction, and the crystal structure was elucidated using single-crystal X-ray diffraction intensities. The molecules are arranged in monoclinic P21/n symmetry allowing for a dihedral angle of 36.76 (8)° observed between the mean plane of the benzene ring and the mean plane of the piperidine chair. Essentially projected non-bonded interactions were corroborated through Hirshfeld surface analysis. Predominant H…H and long-ranged halogen interactions packed with weak dispersion forces suggest the sizeable hydrophobic surface area. The chloro analogue (CPMPM) of FPMPM was compared for its FT-IR and FT-Raman spectra displaying their characteristic vibration modes of the functional groups. The bandgaps of 2.82 and 3.97 eV in FPMPM and CPMPM divulged by the Tauc's plots of UV–vis spectral data are concomitant with the optical band gaps disclosed by photoluminescence spectra. A longer delayed fluorescence lifetime of 31.5(8) and 33.1(1) ns with relatively high contribution confirmed the intermediate triplet state in the materials. The fast, prompt fluorescence decay of 3.72 (2) and 2.85 (1) ns in FPMPM and CPMPM with 54 (1) and 69 (1) % percent fractional contribution are promising shreds of evidence for the materials to act as an optical imaging fluorophore and an imminent scintillating material at moderate temperatures. Relatively moderate values of nonlinear susceptibility (3.44 and 3.85) × 10−6 (e. s. u.) and positive nonlinear absorption coefficient with z-scan measurements supported thermal concave lensing behavior and reverse saturable absorption in both the materials. Thermogravimetry coupled with Differential Scanning Calorimetry (DSC) declares the moderately low melting point (70.4 and 107 °C) for the material, FPMPM, and CPMPM, respectively. The F substituent in FPMPM possesses high hydrophobicity and lipophilicity, mitigating antibacterial activity, while moderate H…F and C-H…π interactions allow for susceptible antimicrobial activities. CPMPM exhibits robust antifungal activity against Trichoderma with reference to amphotericin-B. The antioxidant scavenging property is reflected by relatively high proton reactivity sites in FPMPM and hence relatively low % DPPH activity in CPMPM.