Design, synthesis, and characterization of the electrochemical, nonlinear optical properties, and theoretical studies of novel thienylpyrrole azo dyes bearing benzothiazole acceptor groups (original) (raw)
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Dyes and Pigments, 2012
Two series of novel thermally stable second-order nonlinear optical (NLO) heterocyclic azo dyes 4e5 have been designed and synthesized. The two series of compounds were based on different combinations of acceptor groups (thiadiazole or arylthiadiazole electron-deficient heterocycles) linked to bithiophene which acts at the same time as a donor group and as a p-conjugated bridge. The solvatochromic behavior of azo dyes 4e5 was investigated in several solvents of different polarity, while their thermal stability was evaluated using thermogravimetric analysis. Optimized ground-state molecular geometries and an estimation of the lowest energy single electron vertical excitation energies in DMF solutions were obtained using density functional theory (DFT). Their redox properties were studied by cyclic voltammetry, while hyper-Rayleigh scattering (HRS) was employed to evaluate their second-order nonlinear optical properties. The measured molecular first hyperpolarizabilities and the observed electrochemical behavior showed variations for the different acceptor systems used (thiadiazole or arylthiadiazole) and were also sensitive to the electronic acceptor strength of the substituents (R) linked to thiadiazole or arylthiadiazole heterocycles. Donoreacceptor arylthiadiazole-bithienyl diazenes exhibit the most promising thermal (T d ¼ 237e305 C) and solvatochromic (Dn ¼ 1117e2503 cm À1 ) properties and second order nonlinear optical response (136e226 Â 10 À30 esu).
Photoswitching in azo dyes bearing thienylpyrrole and benzothiazole heterocyclic systems
Dyes and Pigments, 2012
Visible light promotes the conversion of the E-isomer of benzothiazol-2-yl and benzothiazol-6-yl diazenes to the thermal unstable Z-isomer that reverts in few seconds to the initial form. The kinetics of the thermal Z-E process is strongly influenced by the linkage position of the N=N function to the benzothiazole heterocycle. Thienylpyrrole azo dyes functionalized with benzothiazol-6-yl groups are particularly interesting since they show an excellent compromise between the switching speed (rate constants: 0.068-0.12 s-1) and the amplitude of the absorbance variation (37-42%).
Journal of Photochemistry and Photobiology. A, Chemistry
The solvatochromism and other spectroscopic and photophysical characteristics of four azo disperse dyes, derived from 2-amino-5-nitrothiazole, were evaluated and interpreted with the aid of experimental data and quantum mechanical calculations. For the non-substituted compound two conformers, E and Z, were proposed for the isolated molecules, being the second one considerably less stable. The optimization of these structures in combination with a SCRF methodology (IEFPCM, simulating the molecules in a continuum dielectric with characteristics of methanol), suggests that the Z form is not stable in solution. This same behaviour is expected for the substituted compounds, which is corroborated by experimental data presented in previous investigations [A.E.H. Machado, L.M. Rodrigues, S. Gupta, A.M.F. Oliveira-Campos, A.M.S. Silva, J. Mol. Struct. 738 (2005) 239-245].
Thienylpyrrole azo dyes: synthesis, solvatochromic and electrochemical properties
Tetrahedron, 2005
The synthesis and the evaluation of solvatochromic and electrochemical properties of new donor-acceptor-substituted thienylpyrrole azo dyes 3 are described. These derivatives exhibit dramatic changes in both their electronic and redox properties in comparison with thienylpyrroles 1. In agreement with the solvatochromic and electrochemical studies of push-pull derivatives 3 the new compounds prepared, may find application in the manufacture of new materials with notable non-linear optical properties. Recently we have reported the synthesis of thienylpyrroles 1 through a combination of Friedel-Crafts and Lawesson reactions. 28 Compounds 1 have proved to be versatile substrates in diazo coupling reactions, allowing the preparation of several new donoracceptor substituted thienylpyrroles. The synthesis of thienylpyrrole azo dyes 3 is outlined in Scheme 1. The coupling reaction of aryldiazonium salts 2a-d, with 1-alkyl(aryl)-2-(2´-thienyl)pyrroles 1A-H gave rise to the formation of 1-alkyl(aryl)-2-(2´-thienyl)-5-phenylazopyrrole derivatives 3. This functionalization was made by reacting 1-alkyl(aryl)-2-(2´-thienyl)pyrroles 1A-H with aryldiazonium salts 2a-d in acetonitrile/acetic acid for 2h at 0 ºC. Diazo coupling was accomplished selectively at the 5-position 29-30 of pyrrole ring to give compounds 3 in moderate to excellent yields (31-90%), (Scheme 1, ).
Tetrahedron, 2007
The synthesis and full characterization of new chromophores with second-order nonlinearities containing thienylpyrrolyl and benzothiazolyl moieties are reported. The solvatochromic behavior of the compounds was investigated. The hyperpolarizabilities b of derivatives 4-6 were measured using hyper-Rayleigh scattering and thermogravimetric analysis (TGA) was used to evaluate their thermal stability. The experimental results indicate that strong nonlinearity is balanced by good thermal stability especially for chromophores 6b and 6c, making them good candidates for NLO applications.
2-Arylthienyl-Substituted 1,3-Benzothiazoles as New Nonlinear Optical Chromophores
European Journal of Organic Chemistry, 2006
A series of nonlinear optical chromophores 6 containing a substituted benzothiazole ring have been synthesized and characterized. 1,3-Benzothiazoles 6 were prepared by treating various formyl derivatives of thienyl compounds with ortho-aminobenzenethiol in fair to excellent yields. These in turn were prepared by Suzuki coupling between aryl and thienyl precursors. The electronic interactions between donor and acceptor end groups in the conjugated 1,3-benzothiazoles 6 are revealed by the intense and markedly solvatochromic CT transitions. The solvatochromic behaviour of compounds 6 was determined by linear regression analyses of absorption maxima in several solvents, where benzothiazole 6f was found to be a very appropriate indicator dye
Physical Chemistry Chemical Physics, 2010
A detailed spectroscopic and photophysical study has been carried out on a series of heterocyclic compounds-known to display nonlinear optical properties-consisting on a electron donating thienylpyrrolyl p-conjugated system functionalized with an electron acceptor benzothiazole moiety. The absorption, emission and triplet-triplet absorption together with all relevant quantum yields (fluorescence, intersystem crossing and internal conversion), excited state lifetimes and the overall set of deactivation rate constants (k F , k IC and k ISC) were obtained in solution at room (293 K) and low (77 K) temperature. The optimized ground-state molecular geometries for the compounds together with the prediction of the lowest vertical one-electron excitation energy and the relevant molecular orbital contours for the compounds were also determined using density functional theory (DFT) at the B3LYP/3-21G* level. The experimental results showed that the photophysical properties are influenced by the relative position of the pyrrole and thiophene relative to the benzothiazole group.