Synthesis of novel conjugated oligomers for second-order nonlinear optics: incorporation of a central spacer as a conjugation modulator
作者:Jian Xin Zhang、Philippe Dubois、Robert Jérôme
DOI:10.1039/a606547c
日期:——
A new series of second-order nonlinear optical chromophores has
been synthesized that consists of a conjugated segment end-capped with
an electron acceptor and an electron donor, respectively, and a central
spacer intended to modulate the electro-optical effect. Conjugated
chains have been tailored with trans-vinylene-1,5-thienylene as
the building unit and N,N-dimethylamino and nitro
groups as the donor–acceptor pair. Four spacers have been
incorporated into the central part of the conjugated oligomers, which
range from saturated to totally unsaturated functions, i.e.
from methylene to vinylene units. The general strategy relies upon two
consecutive Wittig or Wittig–Horner reactions between the spacer
precursor and an aromatic phosphonium or phosphonate bearing the strong
electron donor and the acceptor, respectively. Two synthetic pathways
have been studied. The first procedure is based on the use of a
symmetric precursor for the spacer. However, a reaction byproduct is
formed, which must be removed and decreases the reaction efficiency. The
second approach requires an asymmetric precursor for the spacer, the
synthesis of which is a multistep process. In order to evaluate the
effect of the spacer, a completely conjugated oligomer has been prepared
by the one-step coupling of two conjugated segments end-functionalized
by the electron donor and the acceptor, respectively.
一种新的二阶非线性光学染料系列已被合成,该系列由一个共轭段组成,两端分别封端为电子受体和电子给体,并包含一个中心间隔器,旨在调节电光效应。共轭链使用反式乙烯-1,5-噻吩单元作为构建单元,N,N-二甲基氨基和硝基作为给体–受体对。四种间隔器被引入到共轭 oligomer 的中央部分,这些间隔器从饱和功能到完全不饱和功能,即从亚甲基到乙烯基单元。一般策略依赖于间隔器前体与带有强电子给体和受体的芳香族膦盐或膦酸酯之间的两次连续 Wittig 或 Wittig–Horner 反应。研究了两条合成路径。第一种程序基于使用对称前体作为间隔器。然而,会形成一个反应副产物,必须去除,这降低了反应效率。第二种方法需要不对称的间隔器前体,其合成是一个多步过程。为了评估间隔器的影响,通过将两个分别被电子给体和受体功能化的共轭段进行一步耦合,制备了一个完全共轭的 oligomer。