Molecular structure tuning impact on optical linearity and nonlinearity of novel push-pull conjugated organic systems for photonic applications

Abstract

In the present work, we have designed and synthesized push-pull conjugated (symmetric d-π-A-π-D type) organic chromophores 2-(2,6-bis((E)-2-(anthracen-9-yl) vinyl)-4H-pyran-4-ylidene)malononitrile (M2) and 2-(2,6-bis((E)-2-(pyren-1-yl) vinyl)-4H-pyran-4-ylidene) malononitrile (M3). These chromophores are the derivatives of 2-(2, 6-dimethyl-4H-pyran-4-ylidene) malononitrile (DPM) with DPM acting as an electron acceptor unit whereas anthracene and pyrene substituents are represented as the electron donor units in M2 and M3 respectively. The structural and photophysical properties of these compounds have been analyzed using IR, NMR, UV–Vis absorption and emission spectroscopies. We comparatively investigated the third-order NLO properties of these novel compounds in CHCl3 for different dye solution concentrations and various laser powers. Moreover, the effect of substitution (electron acceptor unit anthracene and pyrene) on the nonlinear optical properties have been discussed based on the structural modification. The quantum chemical calculations (DFT) were performed to obtain optimized geometry, frontier molecular orbitals, natural bond orbitals (NBO), and NLO parameters of these compounds. The time-dependent density functional theory (TD-DFT) was employed for insight into the electronic structure, photophysical, and NLO properties of these compounds. Experimental results have been supported by the obtained theoretical results.