Nonlinear Optical Properties of Porphyrin, Fullerene and Ferrocene Hybrid Materials

In this research, we investigated the second-order nonlinear optical (NLO) properties of multicomponent hybrid materials formed by meso-tetraphenylporphyrin P (both as free base and ZnII complex), carrying in 2 or 2,12 β-pyrrolic position an electron donor ferrocene (Fc), and/or an electron acceptor fullerene (C60) moiety, connected to the porphyrin core via an ethynyl or an ethynylphenyl spacer. We measured the NLO response by the electric-field-induced second-harmonic generation (EFISH) technique in CH2Cl2 solution with a 1907 nm incident wavelength, recording for all the investigated compounds unexpected negative values of μβ1907. Since density functional theory (DFT) calculations evidenced for P-Fc dyads almost null ground state dipole moments and very low values for P-C60 dyads and Fc-P-C60 triads, our EFISH results suggested a significant contribution to γEFISH of the purely electronic cubic term γ(−2ω; ω, ω, 0), which prevails on the quadratic dipolar orientational one μβ(−2ω; ω, ω)/5kT, as confirmed by computational evidence.

A semi-empirical estimation of ground and excited state dipole moments of zinc phthalocyanine from solvatochromic shift data

A semi-empirical determination of ground and excited state dipole moments of zinc phthalocyanine (ZnPc) from solvatochromic shifts is hereby presented. The ratio of the excited- and ground-state dipole moments of ZnPc ( ) was estimated by a combination of the Bakshiev and the Kawski-Chamma-Viallet’s equations, while the difference in the excited- and ground-state dipole moments (Dm) was estimated usingthe molecular-microscopic solvent polarity parameters ( ), alongside the Stokes’ shifts (Dῡ) in the various solvents. The dipole moment of ZnPc is significantly higher in the excited singlet state (me = 3.12 D) than in the ground state (mg = 1.50 D). Obviously charge separation is greater in the excited state of ZnPc than in its ground state.

Studies on Photophysical Properties of Mono-carbonyl Curcumin Analogues: Experimental and Theoretical approach

The solvatochromic fluorescence behaviour of mono-carbonyl curcumin analogues has been studied in ten different solvents ranging from non-polar to polar. The solvent effect on the spectral properties of analogues has been discussed. The ground state dipole moments were estimated experimentally by Bilot-Kawski equation which is a function of Stokes shift with the solvent polarity parameters and Guggenheim method and theoretically by TD-DFT studies. The excited state dipole moment was determined using Bilot-Kawski equations. The excited state dipole moments for the two molecules were found to be higher than their corresponding ground state dipole moments. Theoretically Frontier molecular orbital (HOMO/ LUMO) energies were determined by Gaussian 09 W software using TD-DFT.

Photovoltaic Effect in Single Layer 1H-Pyrazolo[3,4-b]quinoline and 1H-Pyrazolo[3,4-b]quioxaline/Poly(3-Decylthiophene) Polymer Cells

We have explored photovoltaic (PV) reponse for the pyrazoloquinoline and pyrazoloquinoxaline dyes incorporated into the poly(3-decylthiophene) (PDT) polymer matrices. The photovoltaic response correlates generally with the enhancement of the state dipole moments. Generally we have shown that enhanced state dipole moments lead to an increase of the open circuit voltage. The surrounded polymer matrix of the polythiophene enhances the ground state dipole moments and its relative changes are decreased with the increase of the particular state dipole moments. An appearance of the three-phenyl backside groups substantially diminishes the effect.

Theoretical and Experimental Dipole Moments of Purines

As a follow-up on our previous study of a series of purines (purine, 6-chloropurine, purine-6-thiol, hypoxanthine, theobromine, theophylline, caffeine, and uric acid), we have investigated six additional biologically important purines (adenine, guanine, isoguanine, thioguanine, xanthine, and kinetin). Their ground-state dipole moments were measured in dioxane at 293 K. The first excited singlet-state dipole moments were obtained using the solvatochromic shift equations (McRae, Suppan, Bakhshiev, and Kawski-Chamma-Viallet). The theoretical dipole moments were calculated as a combination of the π-moment (PPP method) and the σ-moment (vector sum of the σ-bond and σ-group moments). The same approach was used to obtain their first excited singlet-state dipole moments (excited state π-moment; σ-moment assumed to be the same as in the ground state). Ab initio HF 6-31G** calculations were also used to obtain ground-state dipole moments for all the fourteen purines under study. In addition, a DFT/B3PW91/6311++(2df,2p) calculation has been carried out for purine for comparison. The different sets of theoretical dipole moments were compared with the respective experimental values. There is an approximately equally good agreement among the experimental dipole moments and the PPP + σ dipole moments (±6.9%) and the ab initio dipole moments (±7.4%). The effect of structure on the dipole moments is discussed.

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.