Department of Chemistry, Indian Institute of Technology Delhi , Hauz Khas, New Delhi 110016, India.
Langmuir. 2017 Sep 26;33(38):9781-9792. doi: 10.1021/acs.langmuir.7b01981. Epub 2017 Sep 6.
Deep eutectic solvents (DESs) have shown potential as novel media to support molecular aggregation. The self-aggregation behavior of two common and popular carbocyanine dyes, 5,5',6,6'-tetrachloro-1,1'-diethyl-3,3'-di(4-sulfobutyl)-benzimidazole carbocyanine (TDBC) and 5,5'-dichloro-3,3'-di(3-sulfopropyl)-9-methyl-benzothiacarbo cyanine (DMTC), is investigated within DES-based systems under ambient conditions. Although TDBC is known to form J-aggregates in basic aqueous solution, DMTC forms H-aggregates under similar conditions. The DESs used, glyceline and reline, are composed of salt choline chloride and two vastly different H-bond donors, glycerol and urea, respectively, in 1:2 mol ratios. Both DESs in the presence of base are found to support J-aggregates of TDBC. These fluorescent J-aggregates are characterized by small Stokes' shifts and subnanosecond fluorescence lifetimes. Under similar conditions, DMTC forms fluorescent H-aggregates along with J-aggregates within the two DES-based systems. The addition of cationic surfactant cetyltrimethylammonium bromide (CTAB) below its critical micelle concentration (cmc) to a TDBC solution of aqueous base-added glyceline shows the prominent presence of J-aggregates, and increasing the CTAB concentration to above cmc results in the disruption of J-aggregates and the formation of unprecedented H-aggregates. DMTC exclusively forms H-aggregates within a CTAB solution of aqueous base-added glyceline irrespective of the surfactant concentration. Anionic surfactant, sodium dodecylsulfate (SDS), present below its cmc within aqueous base-added DESs supports J-aggregation by TDBC; for similar SDS addition, DMTC forms H-aggregates within the glyceline-based system whereas both H- and J-aggregates exist within the reline-based system. A comparison of the carbocyanine dye behavior in various aqueous base-added DES systems to that in aqueous basic media reveals contrasting aggregation tendencies and/or efficiencies. Surfactants as additives are demonstrated to control and modulate carbocyanine dye self-aggregation within DES-based media. The unique nature of DESs as alternate media toward affecting cyanine dye aggregation is highlighted.
深共熔溶剂 (DESs) 已显示出作为支持分子聚集的新型介质的潜力。在环境条件下，在基于 DES 的系统中研究了两种常见且流行的碳菁染料，5,5',6,6'-四氯-1,1'-二乙基-3,3'-二（4-磺丁基）-苯并咪唑碳菁（TDBC）和 5,5'-二氯-3,3'-二（3-磺丙基）-9-甲基苯并噻咯碳菁（DMTC）的自聚集行为。尽管 TDBC 已知在碱性水溶液中形成 J-聚集体，但 DMTC 在类似条件下形成 H-聚集体。所使用的 DES，甘油和雷林，分别由盐氯化胆碱和两种截然不同的氢键供体甘油和尿素以 1:2 的摩尔比组成。在存在碱的情况下，两种 DES 都被发现支持 TDBC 的 J-聚集体。这些荧光 J-聚集体的特征是小的斯托克斯位移和亚纳秒荧光寿命。在类似条件下，DMTC 在基于两种 DES 的系统中形成荧光 H-聚集体和 J-聚集体。在添加到水性碱的甘油 DES 中的 TDBC 溶液中添加低于其临界胶束浓度 (cmc) 的阳离子表面活性剂十六烷基三甲基溴化铵 (CTAB) 显示出 J-聚集体的明显存在，并且随着 CTAB 浓度增加到 cmc 以上，导致 J-聚集体的破坏和形成前所未有的 H-聚集体。DMTC 仅在水性碱添加的甘油 DES 中的 CTAB 溶液中形成 H-聚集体，而与表面活性剂浓度无关。在添加水性碱的 DES 中低于其 cmc 的阴离子表面活性剂十二烷基硫酸钠 (SDS) 通过 TDBC 支持 J-聚集；对于类似的 SDS 添加，DMTC 在基于甘油的系统中形成 H-聚集体，而在基于雷林的系统中存在 H-和 J-聚集体。将碳菁染料在各种添加水性碱的 DES 系统中的行为与在水性碱性介质中的行为进行比较，揭示了相反的聚集趋势和/或效率。表面活性剂作为添加剂被证明可以控制和调节基于 DES 的介质中碳菁染料的自聚集。突出了 DES 作为影响菁染料聚集的替代介质的独特性质。
