Enhanced photochromism of chromen-based colorants near silver nanorods in sol–gel matrix
作者:Mei-Lin Ho、Bo-Jen Chi、Tzu-Yi Hung、Hua-Yang Liao、Jing-Chang Wang、Ting-Yi Wang、Jing-Jong Shyue
DOI:10.1039/c3ce40293b
日期:——
In this article, Ag rods with four different aspect ratios were synthesized at 4, 16, 24, and 32 °C (denoted as Ag4, Ag16, Ag24, and Ag32, respectively) in a solâgel matrix and coated with a photochromic dye, 8-N,N-dimethylamino-2,2-dimethyl-2H-pyrano[3,2-c]chromen-5-one (NN-DDPC-CF, CF denotes the ring-closed form), forming AgX-NN-DDPC-CF (X = 4, 16, 24, and 32). They were prepared, structurally characterized and proven to enhance the reversible photochromism of NN-DDPC. Upon irradiation with UV light at various irradiation wavelengths, the NN-DDPC adsorbed onto the Ag rods in the solâgel underwent a ring opening reaction to produce the opened forms and had a bright yellow reflective appearance. The kinetic results clearly account for the fact that the reaction rate of NN-DDPC-coated Ag rods with different aspect ratios is about 6â11 times faster than NN-DDPC alone due to the excitation of localized surface plasmon resonance (LSPR). A solâgel matrix was also used as a soft environment for NN-DDPC so as to decrease the barrier of the closed form to the opened form and hence, increase the photochromic reaction efficiency. The noteworthy photochromic reaction efficiencies of NN-DDPC-covered Ag rods in the solâgel under irradiation at different irradiation wavelengths were also evaluated. The enhancement factor (E) and the volume percentages of the enhanced areas (FE) in the entire shell of the forward photochromic reaction of Ag4- to Ag32-NN-DDPC, depending on the irradiation wavelengths, i.e. 365, 385, 400, and 415 nm, can be deduced to be 12â42 (13â24%), 6â55 (11â16%), 7â38 (12â22%), and 5â39 (12â22%), respectively. It should be noted that for Ag4- to Ag32-NN-DDPC, the E factors in the forward process show more promising values than the reported results. E values of <30 have been reported in past relevant studies. Moreover, the recovery efficiencies and FE values of Ag4- to Ag32-NN-DDPC have been evaluated. It should be noted that without the addition of Ag nanorods, the recovery process of NN-DDPC is negligible. On the other hand, reversibility experiments for Ag32-NN-DDPC under alternating UV and visible irradiation were carried out for fifteen repeated cycles and the around 90% recovery of the absorbance for Ag32-NN-DDPC in each cycle demonstrated the high degree of reproducibility. Accordingly, it is clear that a future extension of this type of photochromic dye with the assistance of the LSPR of inert-metal nanorods should be versatile and prospective.
在这篇文章中,合成了四种不同长宽比的银杆,分别在4、16、24和32°C下(分别标记为Ag4、Ag16、Ag24和Ag32),它们被包覆在一种光致变色染料8-N,N-二甲氨基-2,2-二甲基-2H-呋喃[3,2-c]香豆酮(NN-DDPC-CF,CF表示闭环形式),形成AgX-NN-DDPC-CF(X = 4, 16, 24, 和 32)。这些银杆经过制备、结构表征,并证明能够增强NN-DDPC的可逆光致变色性。在不同波长的紫外光照射下,吸附在溶胶-凝胶中的NN-DDPC与银杆发生开环反应,产生开环形式,并呈现明亮的黄色反射外观。动力学结果清晰表明,由于局部表面等离子体共振(LSPR)的激发,NN-DDPC包覆的银杆在不同长宽比下的反应速率比单独的NN-DDPC快约6至11倍。溶胶-凝胶基质也作为NN-DDPC的软环境,以降低闭合形式与开环形式之间的反应障碍,从而提高光致变色反应效率。NN-DDPC覆盖的银杆在不同波长照射下的显著光致变色反应效率也得到了评估。根据照射波长(即365、385、400和415 nm),Ag4到Ag32-NN-DDPC前向光致变色反应的增强因子(E)和增强区域的体积分数(FE)可以推断为:分别为12-42(13-24%)、6-55(11-16%)、7-38(12-22%)和5-39(12-22%)。值得注意的是,对于Ag4到Ag32-NN-DDPC,前向过程中的E值显示出比已有报告结果更具潜力,以往相关研究中E值报告为<30。此外,Ag4到Ag32-NN-DDPC的恢复效率和FE值也进行了评估。应当指出,在未添加银纳米杆的情况下,NN-DDPC的恢复过程可以忽略不计。另一方面,对Ag32-NN-DDPC在交替紫外光和可见光照射下进行了15个循环的可逆性实验,每个循环中Ag32-NN-DDPC的吸光度恢复率约为90%,显示了高重复性。因此,可以明确未来这一类型光致变色染料结合惰性金属纳米杆的LSPR,将具有多功能性和前景。