Structural and femtosecond third-order nonlinear optical properties of electron donor – acceptor substituted chalcones: An experimental and computational approach

Abstract

Structural and third-order nonlinear optical (NLO) properties of two D-π-A-π-A [ (2E)-3-(3-chlorophenyl)-1-(3-nitrophenyl)prop-2-en-1-one (3C3NC) and (2E)-3-(4-fluorophenyl)-1-(4-nitrophenyl)prop-2-en-1-one (FNC)] and one D-π-A-π-D [(2E)-1-(9-anthryl)-3-(4-fluorophenyl) prop-2-en-1-one (FANC)] type chalcone derivatives were investigated experimentally as well as theoretically. All the three chalcones are centrosymmetric (CS) and crystallized in P21/c space group. In crystal packing, all compounds exhibit C–H⋯O hydrogen bonds and π···π interactions. From UV–Vis–NIR absorption spectra, the cut-off wavelength and optical band gaps of the chalcones were evaluated. The thermal stability and the melting point of the chalcones were determined from the TGA/DTA techniques. The ultrafast third-order NLO properties of the three chalcones in solution (0.01 M) were evaluated by Z-scan technique using femtosecond (fs) pulses from Ti: Sapphire laser (∼150 fs, 80 MHz, 800 nm). Third-order nonlinear absorption (NLA) coefficient (β ∼ 10−9 cmW−1), nonlinear refraction (NLR) index (n2∼10−14 cm2W−1), susceptibility (χ(3) ∼ 10−12 esu) and molecular hyperpolarizability (γh ∼ 10−31 esu) were unambiguously determined. The chalcones satisfy the condition to observe reverse saturable absorption (RSA) mechanism (σex > σg). Further, the larger values of σex/σg (∼2–3) indicate that the chalcones would exhibit remarkable optical limiting property. The estimated optical limiting (OL) threshold values are in the order of μJ/cm2. Further, all the chalcones have satisfied the one-photon and two-photon figures of merit conditions (W > 1 and T < 1) for the optical switching applications. In addition to experimental findings, the optimized geometry, HOMO-LUMO energy gap, NLO parameters such as electronic dipole moment, polarizability, first and second hyperpolarizabilities of all the three chalcones were determined theoretically (DFT) for different wavelength at B3LYP/6-311 + G (d,p) basic set. The experimentally determined second-order susceptibilities (Z-scan technique) are reasonably in agreement with the computational values (TD-DFT). The MEP surface revealed that the 3C3NC, FNC and FANC molecules have some potential sites for electrophilic and nucleophilic attack. The experimental and computational NLO data clearly suggest that the nonlinearity of chalcone molecules greatly depends on the electron donor and acceptor strengths of the substituents. Further, all the chalcones are potential materials for optical limiting and optical switching applications.