pH-Responsive Switchable Aggregation Phenomena of Xanthene Dyes Adsorbed on Tungsten(VI) Oxide Colloid Surface

Abstract

The surface interactions between xanthene (XN) dyes, including rhodamine B, rhodamine 3B, rhodamine 19, rhodamine 6G, rhodamine 110, and rhodamine 123, and tungsten(VI) oxide (WO 3 ) colloid particles were investigated. These XN dyes were strongly adsorbed as monolayer onto the WO 3 surface via the electrostatic interaction between their peripheral cationic amino-substituents and negatively surfacecharged WO 3 colloid particles, and most of ones adsorbed eventually formed the stable π-stacked dimers.The geometry of dimers formed on the WO 3 colloid surface is discussed on the molecular exciton theory framework. Cationic XN dyes formed the approximately ideal face-to-face H-dimers on the WO 3 colloid surface, whereas zwitterionic ones had a higher tendency to form the oblique J-dimers. Additionally, we have experimentally demonstrated the possibility of pH-induced switching between H-and J-aggregation modes of the XN dye's dimers formed on the WO 3 colloid surface. The findings lead to a better understanding of organic dye's adsorption/aggregation behaviors on the metal oxide surface.

Dimerization of Organic Dyes on Luminescent Gold Nanoparticles for Ratiometric pH Sensing

“…This suggested that the pH did not significantly affect head-to-head coupling between transition dipoles of dimers; however, it did significantly strengthen the head-to-tail coupling between transition dipoles. These changes also implied that the angle between two transition dipoles became larger and the couplings were weaken with pH increase [13] . Therefore, energy transfer between TAMRA dimers became less efficient and emission of TARMA dramatically increased [12a, 12b, 13] .…”

“…An additional small shoulder peak at 522 nm was due to association between monomeric TAMRA molecules in aqueous solution [11] . After the conjugation to GS-AuNPs, the strong absorption at 550 nm was split into two peaks: one peak was located at 522 nm and the other was red shifted to 557 nm, consistent with previous reports [12] on dimerization of TAMRA molecules, further confirming dipole-dipole couplings of TAMRA dimers on GS-AuNPs.Since both blue and red shifts in absorption of TAMRA were observed, according to wellknown molecular excitation coupling theory [12a] , the dimers of TAMRA are not parallel to each other but have intermediate geometries [13] .While both monomeric TAMRA and GS-AuNPs are insensitive to pH changes from 6 to 10 (Figure 2A), TAMRA exhibited strong pH-dependent emission after being conjugated onto GS-AuNPs. As shown in figure 2B, with the increase of the pH value from 6 to 10, the fluorescence intensity at 587 nm gradually increased for more than 5 times while the emission intensity from the GS-AuNPs changed less than 10% in this range.…”

“…Since both blue and red shifts in absorption of TAMRA were observed, according to wellknown molecular excitation coupling theory [12a] , the dimers of TAMRA are not parallel to each other but have intermediate geometries [13] .…”

“…After the conjugation to GS-AuNPs, the strong absorption at 550 nm was split into two peaks: one peak was located at 522 nm and the other was red shifted to 557 nm, consistent with previous reports [12] on dimerization of TAMRA molecules, further confirming dipole-dipole couplings of TAMRA dimers on GS-AuNPs. Since both blue and red shifts in absorption of TAMRA were observed, according to wellknown molecular excitation coupling theory [12a] , the dimers of TAMRA are not parallel to each other but have intermediate geometries [13] .…”

MCM-41@Schiff Base-Mn(OAc)2 Catalyzed Synthesis of Xanthene Derivatives in Water

“…同时, 在 pH 敏感型荧光材料 [4] 、激 光技术 [5] 和染料 [6] 等方面也有很好的应用. 随着氧杂蒽 在各领域上的广泛应用, 其在合成方面备受人们关注, 且在近几年出现了很多合成氧杂蒽的方法 [7～9] .…”