A reactivity index study to monitor the role of solvation on the interaction of the chromophores with amino-functional silanol surface for colorimetric sensors.

Amino-functional silanol surface are mostly used for the immobilization of inorganic ions, molecules, organic or biochemical molecules onto the mesopore surface. In analytical chemistry, the metal ion uptake was visualized through colorimetric sensors using chromophore molecules. One needs to know the structure-property correlation between the chromophore and silylating agent while choosing chromophore, which is very important to design the sensors. We have used two chromophores representative of hydrophobic and hydrophilic type. We used density functional calculation on all the interacting molecules in both the unsolvated phase and solvated medium within the domain of hard soft acid base principle (HSAB) to look at the localized activity of the interacting atoms of these reacting molecules to formulate a priori rule to choose of the best chromophore. We have as well postulated the mechanism of interaction between chromophore and the silylating agent. The results were compared with experiment and it is observed that solvation plays a detrimental role in the binding of chromophore with silylating agent. The results also show that, the range of reactivity index can be used as a suitable property to scale activity of chromophore molecules suitable for the sensing process. It is observed that the hydrophobic chromophore binds stronger with both the metal and the silylating agent; whereas for the hydrophilic one, it binds only with the silylating agent when solvated and in all cases the metal ion binding is weaker compared to that of the hydrophobic one.