Elsevier

Dyes and Pigments

Volume 102, March 2014, Pages 142-149
Dyes and Pigments

Novel second-order nonlinear optical chromophores containing multi-heteroatoms in donor moiety: Design, synthesis, DFT studies and electro-optic activities

https://doi.org/10.1016/j.dyepig.2013.10.042Get rights and content

Highlights

  • A series of novel second-order nonlinear optical chromophores has been synthesized and systematically characterized.

  • The resulting NLO chromophores exhibited both good thermal stability and good solubility in common organic solvents.

  • The film-C displayed the highest r33 value of 31 pm/v at the same doping concentrations of 20 wt%.

Abstract

A series of novel second-order nonlinear optical chromophores containing additional heteroatoms in donor moieties has been synthesized and systematically characterized. The resulting nonlinear optical chromophores exhibited both good thermal stability (the decomposition temperature in the range of 249 °C–275 °C) and good solubility in common organic solvents such as chloroform, acetone and N, N-dimethyl formamide. In order to investigate the influence of additional heteroatom on the electro-optic activities, UV–Vis spectra and density functional theory calculations were carried out. The results revealed that the donor derived from m-phenylenediamine had higher electron density compared with other three donors. As to electro-optic activities, the doped polymer film-C displayed the highest electro-optic coefficient value of 31 pm/v at the doping concentration of 20 wt%. All these results indicated that the nonlinear optical activities could be enhanced by introducing suitable additional heteroatoms into donor moiety.

Introduction

Organic and polymeric electro-optic (EO) materials have drawn much attention because of their attractive potential applications in optical data transmission and optical information processing [1]. Compared with traditional inorganic and semiconductor materials, the organic EO materials have many advantages such as larger nonlinear optical coefficients, simpler preparation and lower cost [2], [3], [4], [5], [6]. Generally, the nonlinear optical (NLO) chromophore molecules possessing a dipolar D-π-A type structure is the core component in such materials, which turned the design and preparation of NLO chromophores into a hot research spot in the area of organic EO materials [7], [8]. Much great attentions have been paid to the rational design of chromophores with not only high first-order hyperpolarizability but also good thermal and photochemical stabilities, and in addition, have good solubility and compatibility with polymer matrix.

It is a well-established fact that the conjugation length and donor/acceptor strength of these D-π-A type push–pull chromophore molecules can cause dramatic influences to their second-order nonlinear responses [3], [5], [6], [7]. In order to search for highly efficient NLO chromophores, finding an optimal combination of their donor/acceptor still represents one of the critical challenges [9], [10], [11]. In the past decade, the researches on NLO chromophores have mainly focused on the design of electron bridges and electron acceptors [12], [13], [14], [15]. However, the electron donors, which are important components of NLO chromophores, have received much less attention as the general class of traditional alkyl and aryl amines were considered to be the idea electron donors and were constantly-used. These amines have been proven to possess suitable energy levels of the nitrogen nonbonding lone pair, which is well matched to donate electrons into the π* of the attached aromatic ring [7], [16].

In recent years several studies have demonstrated that introducing additional heteroatoms into the donor moiety of chromophores could dramatically modulate the conjugation of the π-electron networks and the electronic character of the charge transfer kinetics, which could further influence the chromophores' first-order hyperpolarizability [5], [17], [18], [19]. Meanwhile, additional heteroatoms can also provide abundant opportunities for further modifications [5], [20]. However, such kind of electron donors are usually confronted with problems like their complicated synthetic steps and first-order hyperpolarizability, which are still needed to improved. In order to investigate the influence of additional heteroatoms in traditional donor moiety of the NLO chromophores and to achieve better first-order hyperpolarizability and macroscopic EO activities, we designed a series of chromophores in this article with one or two heteroatoms in ortho-position towards the π-bridge where they can more effectively conjugate with the π-system to donate lone pair electrons. Oxygen atom and nitrogen atom were selected as candidates due to their potential suitable electron-donating abilities. For reasonable comparison, these NLO chromophores all choose 2-dicyanomethylene-3-cyano-4,5,5-dimethyl-2,5-dihydrofuran (TCF) as electron acceptors. 1H NMR, MS and crystal structure analysis were carried out to demonstrated the preparation of these chromophores. Thermal stability, photophysical properties, density functional theory (DFT) calculations and EO activities of these chromophores were systematically studied and compared to illustrate the influences of the suitable additional heteroatoms on rational NLO chromophore designs.

Section snippets

Materials and instrument

All chemicals are commercially available and are used without further purification unless otherwise stated. N, N-dimethyl formamide (DMF) was distilled over calcium hydride and stored over molecular sieves (pore size 3Å). Acetone was dried with anhydrous MgSO4, then distilled and stored over molecular sieves (pore size 3Å). The 2-dicyanomethylene-3-cyano-4-methyl-2,5-dihydrofuran(TCF) acceptor was prepared according to the literature [21]. TLC analyses were carried out on 0.25 mm thick

Synthesis and characterization

Scheme 1 showed the synthetic approach for the chromophores AD. Compounds 9 and TCF were prepared according to the literature [21], [22]. Starting from the aromatic amine or substituted aromatic amine, chromophores AD were synthesized in good overall yields through simple 2–3 step reactions: SN2 substitution reaction with bromoethane, Vilsmeier reaction, and the final Knoevenagel condensation with TCF acceptor. This route has been established for the high yield synthesis of this kind of NLO

Conclusion

A series of organic NLO chromophores with multi-heteroatoms donors have been synthesized and systematically characterized by NMR, MS, UV–Vis absorption spectra, and single-crystal X-ray diffraction methods. The new compounds obtained good yields which are ensured by the simple work-up procedures. Thermogravimetric analysis showed good thermal and thermoxidative stabilities of the four chromophores. The effects of bathochromic and solvatochromic behavior on the UV–Vis absorption were also

Acknowledgments

We are grateful to the Directional Program of the Chinese Academy of Sciences (KJCX2.YW.H02), Innovation Fund of Chinese Academy of Sciences (CXJJ-11-M035) and National Natural Science Foundation of China (No. 11104284 and No. 61101054) for the financial support.

References (37)

  • M.J. Cho et al.

    Prog Polym Sci

    (2008)
  • K.P. Guo et al.

    Dyes Pigm

    (2008)
  • B.K. Spraul et al.

    Tetrahedron Lett

    (2004)
  • S. Suresh et al.

    Tetrahedron Lett

    (2005)
  • H.Y. Huang et al.

    Mater Lett

    (2012)
  • M.C.R. Castro et al.

    Tetrahedron

    (2012)
  • R.M. El-Shishtawy et al.

    Dyes Pigm

    (2013)
  • K.S. Thanthiriwatte et al.

    J Mol Struct

    (2002)
  • F. Kajzar et al.

    Polymeric materials and their orientation techniques for second-order nonlinear optics

  • M. Hochberg et al.

    Nat Mater

    (2006)
  • H. Kang et al.

    Angew Chem Int Ed

    (2005)
  • T.D. Kim et al.

    J Am Chem Soc

    (2007)
  • J.Y. Wu et al.

    Chem Commun

    (2012)
  • C. Zhang et al.

    Chem Mater

    (2001)
  • L.R. Dalton et al.

    Chem Rev

    (2010)
  • M. Lee et al.

    Science

    (2002)
  • S.J. Benight et al.

    J Mater Chem

    (2009)
  • D.R. Kanis et al.

    Chem Rev

    (1994)
  • Cited by (0)

    View full text