Properties of novel azodyes containing powerful acceptor groups and thiophene moiety

An important goal in the development of materials for quadratic nonlinear o ptics is to find chromophore molecules, which have a large beta value. In t he area of electrooptical applications, the early attempts included improve ment of the electronic biasing strengths by increased donor-acceptor streng ths and optimization of conjugation. Replacement of benzene moieties by fiv e-membered conjugated heterocycles increases the electron transmission betw een donor and acceptor groups, owing to lower resonance energy, determining an improvement of beta value. Our approach to design improved nonlinear op tical 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 fr om p-aminobenzaldeide or 2-amino-5-formylthiophene was coupled on the 2-(N- ethylanilino)ethanol; (2) aldehydic group reacted with carbanion of 1,3-ind andione, malonitrile, 3-dicyanovinylindan-1-one, and benzo[b]thiophen-3-(2H )-one-1,1-dioxo by Knoevenagel procedure. mu beta>(*) over bar * (0) values , inferred from EFISH measurements at 1.34 and 1.9 mum using the two-level model, show that the substitution of a benzene ring by a thiophene one dete rmines a general enhancement of the hyperpolarizability up to three times t han the DR1 (450 x 10(-48) esu). Solvatochromic data are in agreement. Anal ogous effect is observable in benzene series inserting the vinyldicyano gro up on indandione moiety. Thermal stability was evaluated by TG-DTA. Decompo sition temperatures appear lower than DRI (260-299 degreesC) and, in genera l, chromophores with improved nonlinearity exhibit decreased thermal stabil ity, but again exceeding 200 degreesC, limit value as far as the processing and device fabrication is concerned. (C) 2000 Elsevier Science S.A. All ri ghts reserved.