Development of Non-linear Optical Material involving the Boron Atom

到目前为止，每个共轭体系都由一个施主、一个芳香环和一个受体组成，是众所周知的非线性光学材料，特别是用于产生二次谐波。我们认为芳环的主要作用是减少电子基态中给电子体对受体的电子给予，从而相对增强电子激发态中的相互作用。尽管这些体系具有显著的效率，但最近的研究强调，芳环的闭壳性赋予了体系作为非线性光学材料的上限。三价硼与碳正离子是等电子的。因此，它的行为就像一个pi电子受体。然而，由于它的电性，它与碳原子的pi型共轭被认为是像闭壳芳环一样弱的。从这一观点出发，我们研究了与杂烯有关的钻柱，如TH…。更多的e吡咯或噻吩环，它们都是电子供体。经过多次尝试，合成了1-苯基硫代-[3，4-d]苯基吡咯(1)、1-苯基硫代[2，3-d](2)、5-甲基-1-苯基吡咯[3，4-d](3)和5-三(异丙基硅基)-1-苯基吡咯[3，4-d](4)。所开发的方法一般可用于合成含硼原子的共轭芳香族化合物。随着胡椒环和杂醇环的环化方式的改变，对乙酸的反应活性有显著差异。荧光发射的位移与溶剂极性的变化呈明显的线性关系，表明各化合物在激发态的偶极矩远大于基态的偶极矩。尽管激发态具有上述电荷转移特性，但观察到了适度的蓝光透过率。这些发现表明，含硼原子的共轭体系作为非线性光学材料是有用的。较少

To date, conjugated systems, each being composed of a donor, an aromatic ring and an acceptor, have been the well-known non-linear optical materials, in particular, for the purpose of second harmonic generation. We consider that the main role of the aromatic ring are to decrease donation of pi-electron from the donor to the acceptor in the electronically ground state and, accordingly, to relatively enhance the interaction in the electronically excited state. In spite of the marked efficiency of these systems, the recent examinations have stressed that the closed-shell character of the aromatic rings endows the systems with the upper-limit as non-linear optical materials.A trivalent boron is isoelectronic to a carbocation. Hence, it behaves as a pi-electron acceptor. Due to the electropositivity, however, its pi-type conjugation with the carbon atom is considered to be weak like the closed-shell aromatic rings. From this viewpoint we examined borepin annelated with heteroles, such as th … More e pyrrole or thiophene rings both of which are electron donors. After some trials, synthesis of 1-phenylthieno- [3,4-d] borepin (1), 1-phenylthieno [2,3-d] borepin (2), 5-Methyl-1-phenylpyrrolo [3,4-d] borepin (3), and 5-tris (isopropylsilyl)-1-phenylpyrrolo [3,4-d] borepin (4) were achieved. The methods developed are generally useful for the synthesis of conjugated aromatics involving a boron atom. The marked difference in reactivity toward acetic acid was observed with the change of the annelation modes of borepin and heterole rings. The shifts of fluorescent emissions showed the clear linear relationship with the change of solvent-polarity and indicated that the dipole moment of each compound in the excited state is much larger than that in the ground state. The moderate blue-light transparency was observed, despite the above-mentioned charge-transfer character in the excited state.These findings indicate that conjugated systems involving the boron atom are useful as non-linear optical materials. Less