New conjugated polyenes with 1,3-dialkyl-2-thiobarbituric acid moiety as materials for nonlinear optics: theoretical calculations, synthesis and spectral properties

In this work we report the results of our study on electronic and spectral properties of conjugated polyenes with electron-accepting 1,3-dialkyl-2-thiobarbituric acid moiety. In model calculations, we examine the effect of the conjugated polyene length on infrared (IR) and Raman spectra of the polyenes by means of ab initio HF/3-21G*. Nonlinear properties were also studied by AM1 method in frames of the sum-over-states (SOS) and finite-field formalism. It was concluded that in well-resolved IR and Raman spectra the frequencies and band intensities can provide valuable information relating to C=C bond lengths in polyene chain and relative polarizabilities. Near-linear correlation between polarizability and integral IR band intensity, corresponding to all C=C stretching modes, and the rather nonlinear relationship of polarizability with integral Raman activity, was found. In our calculation we predict that polarizability and the first hyperpolarizability increases with elongation of polyene chain while the second hyperpolarizability increases smoothly in a quadratic way. In contrast to the linear relationship between polarizability and polyene chain length the dipole moment versus chain length is predicted to be nonlinear. A good agreement was found between experimental and calculated Raman spectra of one newly synthesized compound studied.

Electronic structure and nonlinear optical properties of model push-pull polyenes with modified indanone groups: a theoretical investigation

Several model polyenes with modified indanone groups were studied by means of density functional theory (DFT) B3LYP/6-31G*, ab initio HF/3-21G* and semiempirical AM1 methods. We investigated the effect of several substituents upon the relationship between the structure, spatial distribution of the highest occupied and the lowest unoccupied pi-MOs, a concept of the global softness and the global hardness as well as both linear and nonlinear polarizabilities for the set of pi-electron chromophores represented by the short-chain model polyene (butadiene) carrying out p-methoxyphenyl group on the one end and several modified indanone groups on the opposite end of the molecule. As probing endocyclic groups used to modify the structure of indanone the following substituents: > CH2; > C=O; > SO2, > C=CH(NO2) and > C=C(CN)2 were selected. The cubic relationship between the polarizability and the global softness was found. The highest polarizabilities (alpha, beta, gamma) are predicted for the derivatives with > C=C(CN)2 group. It was found that the value of beta depends mainly on the difference between dipole moments in the excited and ground states of the molecules. In the case of > SO2 group the results of AMI calculations significantly deviate from relationships found for other derivatives. Experimental IR and Raman spectra of newly synthesized indandione derivative of cinnamaldehyde were compared with computed ones.