Unconventional Langmuir–Blodgett films: alignment of an optically nonlinear dye where the donor and π-electron bridge are hydrophobic and the acceptor is hydrophilic
作者:Geoffrey J. Ashwell、Alison A. Maxwell、Andrew Green
DOI:10.1039/b200565b
日期:——
The optically nonlinear dye, 5-4-[2-(4-dibutylaminophenyl)vinyl]benzylidene}-2-(1-ethylpropyl)-5,6,7,8-tetrahydroisoquinolinium bromide (1a), differs from other LangmuirâBlodgett (LB) film-forming materials. The molecule is amphiphilic and, therefore, may be aligned at the airâwater interface but, instead of a conventional aliphatic tail, has an extended Ï-electron bridge. It forms non-centrosymmetric LB films which exhibit second-harmonic generation (SHG) and have a high second-order susceptibility: Ï(2)zzz
= 40 pm Vâ1 at 1.064 µm for a monolayer thickness of 1.8 nm and chromophore tilt angle of 55° from the substrate normal. The octadecyl sulfate salt (1b) also forms non-centrosymmetric films but with improved properties: Ï(2)zzz
=
90 pm Vâ1 at 1.064 µm for d
= 2.4 nm and Ï
= 33°. Both films exhibit charge-transfer bands at 360 nm but with absorbance cut-off above 560 nm for 1a and 530 nm for 1b. The latter is fully transparent at the fundamental and harmonic wavelengths and its susceptibility is the highest to date for such a film. This results from an optimised packing arrangement, a conjugation enhanced molecular hyperpolarisability of β
= 4.3 Ã 10â38 m4 Vâ1, and the proximity of the absorption band, albeit non-overlapping at 532 nm. The properties are compared with those of conventional long alkyl tailed materials (2 and 3) of the same chromophore.
光学非线性染料 5-4-[2-(4-二丁基氨基苯基)乙烯基]亚苄基}-2-(1-乙基丙基)-5,6,7,8-四氢异喹啉溴化物 (1a) 与其他 Langmuir 不同。 Blodgett (LB) 成膜材料。该分子是两亲性的,因此可以在空气-水界面处排列,但不是传统的脂肪族尾部,而是具有延伸的π电子桥。它形成非中心对称的 LB 薄膜,表现出二次谐波产生 (SHG) 并具有高二阶磁化率:Ï(2)zzz
= 40 pm V-1 at 1.064 µm,单分子层厚度为 1.8 nm,发色团与基底法线的倾斜角为 55°。十八烷基硫酸盐 (1b) 也形成非中心对称薄膜,但具有改进的性能:Ï(2)zzz
=
晚上 90 点 Vâ1 在 1.064 µm 处持续 d
= 2.4 nm 和 Ï
= 33°。两种薄膜均在 360 nm 处呈现电荷转移带,但 1a 的吸光度截止值高于 560 nm,1b 的吸光度截止值高于 530 nm。后者在基波和谐波波长下是完全透明的,其敏感性是迄今为止此类薄膜中最高的。这是由于优化的堆积排列、共轭增强的 β 分子超极化性所致
= 4.3 × 10−38 m4 V−1,以及吸收带的接近度,尽管在 532 nm 处不重叠。将这些性能与相同发色团的常规长烷基尾材料(2 和 3)的性能进行了比较。