Properties of novel azodyes containing powerful acceptor groups and thiophene moiety

• Published in: Synthetic metals 2000-11, Vol.115 (1), p.213-217
• Main Authors: Ledoux, I, Zyss, J, Barni, E, Barolo, C, Diulgheroff, N, Quagliotto, P, Viscardi, G
• Format: Article
• Language: English
• Subjects: Azobenzene; Azodyes; Degradation temperature; EFISH; Exact sciences and technology; Frequency conversion; harmonic generation, including high-order harmonic generation; Fundamental areas of phenomenology (including applications); Harmonic generation, frequency conversion; NLO properties; Nonlinear optics; Optical materials; Optics; Other nonlinear optical materials; photorefractive and semiconductor materials; Physics; Thiophene
• ISSN: 0379-6779; 1879-3290
• DOI: 10.1016/S0379-6779(00)00337-4

An important goal in the development of materials for quadratic nonlinear optics is to find chromophore molecules, which have a large β value. In the area of electrooptical applications, the early attempts included improvement of the electronic biasing strengths by increased donor-acceptor strengths and optimization of conjugation. Replacement of benzene moieties by five-membered conjugated heterocycles increases the electron transmission between donor and acceptor groups, owing to lower resonance energy, determining an improvement of β value. Our approach to design improved nonlinear optical chromophores is based on the employment of both strong acceptor group and thiophene ring instead of benzene in a mixed azobenzene–stilbene like chromogen. The synthesis was performed in two steps: (1) diazonium salts from p-aminobenzaldeide or 2-amino-5-formylthiophene was coupled on the 2-( N-ethylanilino)ethanol; (2) aldehydic group reacted with carbanion of 1,3-indandione, malonitrile, 3-dicyanovinylindan-1-one, and benzo[b]thiophen-3-(2H)-one-1,1-dioxo by Knoevenagel procedure. μβ(0) values, inferred from EFISH measurements at 1.34 and 1.9 μm using the two-level model, show that the substitution of a benzene ring by a thiophene one determines a general enhancement of the hyperpolarizability up to three times than the DR1 (450×10 −48 esu). Solvatochromic data are in agreement. Analogous effect is observable in benzene series inserting the vinyldicyano group on indandione moiety. Thermal stability was evaluated by TG-DTA. Decomposition temperatures appear lower than DR1 (260–299°C) and, in general, chromophores with improved nonlinearity exhibit decreased thermal stability, but again exceeding 200°C, limit value as far as the processing and device fabrication is concerned.