Synthesis of a kind of poly[thiophene methines] with azo side groups and research on its third order nonlinearity

With the aim of enhancing the nonlinear optical property of poly (thiophene methines), poly[(thiophene-2,5-diyl)p-(N,N-dimethylamino) azobenzylidene] (PTDMAAB) is prepared from 4-aldehyde-4'-dimethylamino azobenzene (ADMAA) and thiophene through condensation polymerization reaction. Then PTDMAAB is oxidized to final polymer-poly[(thiophene-2,5-diyl)p-(N,N-dimethylamino) azo-benzylidenequinomethane](PTDMAABQ). The PTDMAABQ and PTDMAAB are characterized by infrared absorption spectrum (IR), ultraviolet-visible absorption spectrum (Uv-Vis) and proton magnetic resonance spectrum. Compared with PTDMAAB, PTDMAABQ has an enlarged absorption peak at 1650 cm^-1 in its IR spectrum and absorption peak red moves 35 nm in Uv-Vis spectrum, indicating that PTDMAAB has been successfully oxidized and the quino-structure is formed. The X-ray diffraction spectrum of PTDMAABQ shows that there exists a tiny crystallized region. The study of thermal stability by thermal gravity analysis indicates that thermal decomposition temperature of PTDMAABQ is greater than 275°C. The PTDMAABQ films have rather big nonlinear refractive index and 3rd nonlinear coefficient, i.e. 4.926×10^-6 and 3.644×l0^-9 esu, respectively analyzed by Z-scan system.