Structure and Reactivity of Thiazolium Azo Dyes: UV–Visible, Resonance Raman, NMR, and Computational Studies of the Reaction Mechanism in Alkaline Solution

Real-time monitoring of multicomponent reactive dye adsorption on cotton fabrics by Raman spectroscopy

Accurate real-time determination of each dye in combination dyeing is critical to the control of dyeing process, which plays an important role in upgrading the dyeing techniques of textile. In this work, Raman spectroscopy was applied to dyeing baths containing multiple dye species of varying structures to quantitatively monitor the dyeing process of each individual dye. Quantitative models were successfully established by partial least squares (PLS) for all combinations of the nine commonly used reactive dyes studied. The correlation coefficients were greater than 0.99, the root mean squared errors of calibration (RMSEC) were less than 0.2650 and the root mean squared errors of prediction (RMSEP) were less than 0.1340, even for the three-component mixture of Reactive Red 239 (RR239), Reactive Yellow 176 (RY176) and Reactive Blue 194 (RB194), which are similar in structures. The model was shown to be valid in the presence of added electrolytes (sodium sulfates). Real-time adsorption monitoring based on the model revealed that the dyes interacted with one another and competed for active sites. The adsorption kinetics obtained by Raman analysis shed light on dye compatibility and could be used to guide the design of dyeing recipe and dyeing process for optimum color reproduction. In addition, in situ monitoring by Raman spectroscopy maybe integrated with real-time on line control of dyeing parameters for fully automated production of dyed fabrics.

Dyes in Liquid Crystals: Experimental and Computational Studies of a Guest-Host System Based on a Combined DFT and MD Approach

Practical applications of guest–host liquid crystal systems are critically dependent on the alignment of the guest species within the liquid crystal host. UV/Vis absorption spectroscopy shows that the 1,5-dihydroxy-2,6-bis-(4-propylphenyl)-9,10-anthraquinone dye aligns within the E7 nematic host, giving an experimental dichroic ratio of 9.40 and dye order parameter of 0.74. This alignment was modelled by using a combination of density functional theory (DFT) and molecular dynamics (MD) computational approaches that do not require the input of experimental data. Time-dependent DFT calculations show that the electronic transition dipole moment is highly aligned with the long molecular axis of the dye. Fully atomistic MD simulations show that the long axis of the dye is less highly aligned within the E7 host, indicating that this contribution limits the overall dye alignment and, thereby, the potential practical applications of this particular system. Importantly, this study demonstrates an experimental and combined DFT and MD computational approach that may be applied generally to guest–host systems, providing a potential route to their rational design.

Ring transformation of (4-chloro-5H-1,2,3-dithiazol-5-ylidene)acetonitriles to 3-haloisothiazole-5-carbonitriles

Improved conditions for the ring transformation of 1,2,3-dithiazoles into isothiazole-5-carbonitriles are presented together with mechanistic rationale.