作者:A. J. Kay、A. D. Woolhouse、G. J. Gainsford、T. G. Haskell、C. P. Wyss、S. M. Giffin、I. T. McKinnie、T. H. Barnes
DOI:10.1039/b103148c
日期:——
A suite of zwitterionic pyridylidene-based merocyanines that contain no interconnecting π-bridge between the donor and acceptor rings has been synthesised and their second-order NLO properties evaluated largely by semi-empirical computational methods (MOPAC 97/AM1). Contrary to expectation, increasing the degree of inter-ring twist (θ), at least up to 55°, in these new pyridylideneazolone chromophores is found to have little or no effect on the figure of merit [μβ(0)]. An X-ray crystallographic appraisal of one of these chromophores, 14, reveals however that the twist angle (albeit in the solid state) is greater than that predicted by computation and that all other features are consistent with the highly zwitterionic nature of these systems. In spite of this, a combination of factors—insufficient acceptor strength, insufficient extent
of conjugation and perhaps insufficient twist angle, in particular—clearly leads to the low values of the quadratic hyperpolarisabilities. The trade-off between targeting a more modest β from a minimum of π-conjugating framework between D and A (and therefore synthetic expediency) and seeking a moderate-to-high dipole moment has therefore resulted in only low figures of merit for these systems.Calculations performed on a suite of readily accessible, isoelectronic cyanines, in which the acceptor is a stabilised cyclopentadienide carbocycle rather than a heterocycle, have revealed the potential that these systems, exemplified by 27, have as NLO chromophores. Representative polymer-tetherable derivatives of this system have been prepared as have the corresponding TDI-based polyurethanes.
合成了一系列不含捐赠体与受体环之间相互连接π桥的氨基吡啶基美罗青(merocyanine),并主要通过半经验计算方法(MOPAC 97/AM1)评估了它们的二阶非线性光学(NLO)特性。与预期相反,在这些新的氨基吡啶基氮酮色素中,增加环间扭转角度(θ),至少到55°,对性能指标[μβ(0)]几乎没有影响。然而,对其中一种色素14进行的X射线晶体学评估显示,虽然在固态中,扭转角度超过了计算预测的值,并且所有其他特征与这些系统的高度双性离子特性一致。尽管如此,一系列因素——如受体强度不足、共轭程度不足以及可能的扭转角度不足——显然导致了二次超极化率的低值。因此,在以D和A之间的最小π共轭框架为目标来获得更适度的β(因此在合成上的便利性)和寻求适度至高偶极矩之间进行了权衡,结果导致了这些系统的性能指标仅为低值。对一组易于获得的等电子氰类色素进行的计算显示,以稳定的环戊二烯基碳环作为受体,而非杂环的这些系统(以27为例)作为NLO色素具有潜力。已经制备了该系统的代表性聚合物连接衍生物,以及相应的基于TDI的聚氨酯。