Design and syntheses of efficient and thermally stable diamino chromophores for NLO application
Wei Wu, Cheng Ye and Dong Wang*
Institute of chemistry, Chinese Academy of Sciences, Beijing 100080, China
E-mail:
[email protected]
Dedicated to Professor Zhi-Tang Huang on his 75th birthday
(received 25 Oct 02; accepted 20 Jan 03; published on the web 28 Jan 03)
Abstract
A novel series of diamino imidazole-type chromophores has been synthesized, which can be chemically incorporated into polymer matrices. Furthermore, their molecular optical nonlinearity, transparency and thermal stability were determined and studied comparatively. Theoretical calculation and experimental results indicate that good nonlinearity-transparency- thermal stability is well balanced in chromophore 4, which possesses a µgß0 of 554.8×10-48esu, a rather blue-shifted absorption peak at 384 nm in THF, and a high decomposition temperature Td of 377°C. It is strongly suggested from these results that multiple substitution strategy should be useful for designing novel NLO chromophores.
Keywords: Diamine-imidazole-type chromophore, NLO, thermal stability
Introduction
Organic molecules with large first hyperpolarizabilities (ß) have drawn considerable attention over the last 20 years for their potential applications in optical data storage, telecommunications and optical signal processing1,2. It is already well known that molecules that contain electron- donor and electron-acceptor groups separated by a large conjugated framework possess large values of ß.3 Many of these chromophores fall into the category of substituted benzenes, biphenyls, Schiff bases, stilbenes, azo stilbenes and tolans4,5. Molecular nonlinearities can be enhanced significantly by increasing the donor and acceptor strength or the length of the conjugation pathway.6
Although significant progress has accrued in the design and synthesis of such one- dimensional dipole chromophores7,8, other properties, such as transparency, thermal stability and capability to be incorporated into bulk materials must also be optimized. Most NLO chromophores synthesized for electro-optic and frequency doubling application typically exhibit trade-off between nonlinearities and each of the other properties.9,10 For those traditional D- p-A chromophores, the increase in NLO response is usually accompanied by bathochromic shifts of the maximum absorption peak and decrease in thermal stability.
