Theoretical Study Of The Nonlinear Optical Properties Of Benzothiadiazole Derivatives With D-π-A Structure

Organic materials with nonlinear optical (NLO) properties are currently veryimportant in high-technology field and attracting considerable attention because of theirpotential applications in optoelectronic devices of telecommunications, information storage,optical switching, and signal processing. The searching and designing of high-performanceNLO materials is the main task in this field. The organic compounds with D-π-A structurereveal good NLO activity by theoretical study of the NLO property about a series of organiccompounds, and these organic compounds has been supposed to be new generationmultifunctional NLO materials by more decorating.The nonlinear optics and nonlinear optical materials and briefly summarized researchprogress of the organic nonlinear optical materials with D-π-A structure were introduced inthis paper.Four basic theoretical simulation about the nonlinear optical properties,those weremolecular orbital (MO) theory, HF self-consistent field, semi-empirical calculational methodand density functional theory (DFT), and two kinds of commonly-used methods calculatingnonlinear optical susceptibility that were finite-field method(FF) and completely summationmethod (SOS) were reviewed briefly.Multiple series of benzothiadiazole derivatives with D-π-A structure and differentpush-pull electronic group were esigned in this research work. The symmetric or asymmetricπ-conjugated bridge of benzothiadiazole derivatives were lengthen with carbon-carbondouble bond or graphene nanoribbon. The nonlinear properties of this benzothiadiazolederivatives were calculated by semi-empirical finite filed/AM1method of Mopac2009in CSChem3D Ultra12.0. The calculation results show that:(1) When the length of π-conjugatedbridge with graphene nanoribbon was the same long as π-conjugated bridge withcarbon-carbon double bond, π-conjugated bridge with graphene nanoribbon has a greaterimpact on the hyperpolarizability of title molecules than π-conjugated bridge withcarbon-carbon double bond.(2) Compared to the title molecule with asymmetric increase ofπ-conjugated bridge, the second-order hyperpolarizability β and third-orderhyperpolarizability γ of the title molecule with symmetric increase of π-conjugated bridge hasa greater undulating increase.(3) For the title molecules with short π-conjugated bridge, there was a good linear correlation between polarizalbilities and π-conjugated length. For the titlemolecules with longer π-conjugated bridge, the hyperpolarizability of the title moleculeswas undulating increase with the increase of π-conjugated bridge.(4) Compared to someangular molecules and the molecules including donor-graphenenanoribbon-acceptor,thepolarizalbilities or hyperpolarizability of some linear molecules containing graphenenanoribbon was larger increase with the increase of π-conjugated bridge.(5) The strongerpush-pull electronic group imposed on the electric charge, the greater the degree of the chargetransfer and the greater the nonlinear optical polarizability. Trinitrofuran performed well thanTricyanofuran on electron withdrawing ability and then has a greater impact on thehyperpolarizability of title molecules.(6) The relationship of second-orderhyperpolarizability β of the partial molecules with α ΔE-1, third-order hyperpolarizability γwith α ΔE-2and β ΔE-1was a good correlation. Anyway, benzothiadiazole derivatives withD-π-A structure was expected to become the candidate of high performance nonlinear opticsmaterials.