Theoretical study on naphthyl-phenylacetylenes for second-order nonlinear optical applications

The ground state dipole moments (μg), excited state dipole moments (μe), linear polarizabilities (α), first hyperpolarizabilities (β), and absorption maxima [Formula: see text] of a new series of 6,4′-disubstituted 2-naphthylphenylacetylenes have been calculated using the finite field – MNDO (Modified Neglect of Diatomic Overlap) technique and studied for second-order nonlinear optical (NLO) applications. Among all the molecules studied here, the strongest and the weakest electron donor/acceptor pairs [N(CH3)2/NO2] and [CH3/CN] exhibit the largest and the smallest βμ (projection of β on the axis of the μ) of 46.3 × 10−30 esu and 10.2 × 10−30 esu, respectively. The coefficients of the power law that describes the dependence of α and β on the number of conjugated bonds (n) were calculated for [NH2/NO2]n=1–5 and [NH2/CN]n=1–5 molecules. For β, exponents of 0.36 and 0.31 were obtained for [NH2/NO2]n=1–5 and [NH2/CN]n=1–5 molecules, respectively, and for α, an exponent of 0.37 was obtained for both series of molecules. A comparison is made between naphthylphenylacetylenes and diphenylacetylenes on the basis of their hyperpolarizabilities. Keywords: nonlinear optics, organic molecules, hyperpolarizabilities.