Linear and nonlinear optical properties of the twelve styryl dyes are investigated using density functional theory (DFT). Range-separated hybrid CAMÀ B3LYP and global hybrid BHandHLYP estimate high second order hyperpolarizability. Mean polarizability (α 0 ), polarizability anisotropy (Δα), static first-order hyperpolarizability (β 0 ) and second hyperpolarizability (γ) were found to be overestimated in CAMÀ B3LYP than in BHandHLYP. As bond length alternation (BLA) increases first order hyperpolarizability increases. Multilinear regression analysis (MLR) shows the solvent basicity, polarizability and dipolarizabilty are responsible for absorption solvatochromism. The ratio of the dipole moments increases as donor strength and conjugation increases which support charge transfer. The figure of merit (FOM) and intrinsic hyperpolarizability found more in chromophores with dialkylamine donors. As the stability indicated by electrophilicity indices decreases the hyperpolarizability increases. Interrelationships between α 0 , β 0 and γ were evaluated and it shows good linear fit. Absorption is red shifted and hyperpolarizability increases with the amplitude of the sine-shaped potential along the conjugation chain. A high molecular electrostatic potential was observed in dyes containing 2-piperidinothiophene donor. Figure 1. 2-(1,1-dioxidobenzo[b]thiophen-3(2H)-ylidene)malononitrile2-(1,1dioxidobenzo[b]thiophen-3(2H) ylidene)malononitrile
Analogs of 2-[(2Z)-2-[[4-(dihexylamino)-2-methylphenyl]methylidene]-1,1-dioxo-1-benzothiophen-3-ylidene]propanedinitrile (Foron blue SR, Disperse Blue 354) are studied in terms of photophysical, structural aspects and its nonlinear optical properties evaluated by using Density Functional Theory (DFT) and Time Dependent Density Functional Theory (TD-DFT). The structures were optimized by using function B3LYP and basis set used was 6-31G(d). Polarizability (α), first and second order hyperpolarizability (β and γ) was determined by three density functionals B3LYP, CAM-B3LYP and BHandHLYP. B3LYP functional and the basis set 6-311+G(d,p) shows high values of α, β and γ. The B3LYP functional gives the highest first order hyperpolarizability value for (Z)-2-(2-(4-(dimethylamino)benzylidene)-1,1dioxidobenzo[b]thiophen-3(2H)-ylidene)malononitrile (3a) is 373.31 × 10 −30 e.s.u and 486.32 × 10 −30 e.s.u in ethylacetate and dimethylformamide respectively. Effect of bond length alteration (BLA) and bond order alteration (BOA) on first order hyperpolarizability was evaluated. Intrinsic hyperpolarizability shows the compound (Z)-2-(4-(dimethylamino)benzylidene)benzo[b]thiophen-3(2H)-one 1,1-dioxide (1a) intrinsically good. Perturbation potential is found to decrease as absorption energy deceases and hyperpolarizability increases.
A set of linear and asymmetric coumarin–imidazole hybrid compounds having a N,N‐diethylamine at 7‐position and imidazole at 3‐position on the coumarin were synthesized. Insertion of thiophene π‐spacer between coumarin and imidazole moieties (5b, 5d) leads to redshifted absorption and emission compared to 5a and 5c. All the compounds show a noticeable response to trifluoroacetic acid with a redshifted absorption and an increase in emission intensity by twofold. The ratio of ground and excited state acidity constant was calculated using Förster energy cycle, and the ratios were found to be 0.25, 0.96, 0.52 and 1.87, respectively, for 5a‐5d. Due to the thiophene π‐spacer, elongation of π‐conjugation in 5b and 5d leads to high values of polarizability (α), first‐order hyperpolarizability (β) and second‐order hyperpolarizability (γ). Compound 5b exhibits a high value (895 GM) of two‐photon absorption cross section (σ2PA), measured using two‐level model.
Density functional theory (DFT) and time-dependent DFT computations were employed to examine linear and nonlinear optical (NLO) characteristics of (E)-4-((1,1-dioxido-3-oxobenzo[b]thiophen-2(3H)-ylidene) ethyl)-1-phenyl-1H-pyrazol-5(4H)-one derived styryl dyes. NLO properties were computed using the two different global hybrid functionals B3LYP, BHandHLYP and three range separated hybrid functionals CAM B3LYP, wB97, wB97X and wB97XD with the basis sets 6–311++G(d,p), cc-pVDZ and cc-pVTZ. The compounds shows higher values of dipole moment around 8–9 Debye than the other compounds. They show higher values of α
0, ß
0 and γ
0 values. The values of γ
0 are around 204–544 × 10−36 e.s.u. with the method, B3LYP/6–311++G(d, p). We have calculated the mean absolute error (MAE) for dipole moment, α
0, ß
0 and γ
0 values. It is observed that MAE is less (0.89) for wB97/6–311++G(d,p) which indicates that wB97 is the most suited functional for all three compounds. Chemical stability and reactivity of these dyes were studied using electrophilicity index and chemical hardness and hyperhardness.
Novel fused polycyclic benzimidazole derivatives were synthesized from dimethyl 4,5-diaminophthalate/dimethyl 3,4-diaminophthalate with aromatic anhydride (a-b) by condensation. The UV-Visible absorption and fluorescence emission spectra of the dyes were studied in solvents of differing polarity. The dyes were characterized by the spectral analysis. Density Functional Theory computations have been used to derive more understanding of structural, molecular, electronic and photophysical parameters of the push-pull dyes. The computed absorption wavelength values were observed to be in good agreement with the experimental results. The second order hyperpolarizability (β(o)) values were computed by Density Functional Theory and found to be in the range of 67.16 × 10(-31) to 107.76 × 10(-31) e.s.u.
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