Luminescent Molecule/Mesoporous Molecular Sieves As Assembly Sensing Materials

In recent years, the discoveries of sensing materials and devices have become extremely important in environmental and biological fields. A remarkable development of luminescent chemosensing materials has already been made because of their high sensitivity and selectivity. But the study is still localized on characteristics of compounds, it is a key for application that how to turn the compounds into materials and then to form devices. It is demonstrated that the direction in this field is to design and synthesize luminescent molecules and suitable matrix and then to assemble the molecules into the matrix to form materials or devices. So the development of new matrix is an important step for the sensing materials and devices. In this article we use mesoporous molecular sieves as a new class of matrix due to their high surface areas, ordered pore structure, narrow pore size distribution and hydroxyl-covered surfaces and select some organic or complex molecules with fine luminescent chemosensing properties. Then these functional molecules could be physically or chemically incorporated into mesoporous materials to obtain sensing materials, here mainly refer to oxygen sensing materials and metal ion sensing materials. Oxygen sensing material is usually composed of two parts, a support matrix and functional molecules of which the luminescent intensity is depended on the oxygen concentration. Oxygen molecule can quench the luminescence of the functional molecules through the pore of the matrix. Five diimine ruthenium complexes [Ru(bpy)3]2+, [Ru(dtBubpy)3]2+, [Ru(phen)3]2+, [Ru(dphphen)3]2+ and [Ru(tmephen)3]2+, have been synthesized and incorporated into MCM-41 to form sensing materials. The luminescent intensities of these materials decrease with increasing the oxygen concentration. The sensitivity I0/I100 (where I0 and I100 represent the detected luminescent intensities of the oxygen sensing materials exposed to 100% nitrogen and 100% oxygen, respectively.) satisfies the requirement of oxygen sensing materials, the quenching time is less than 2 s and the recovery time is less than 8 s. Especially of [Ru(tmephen)3]2+/MCM-41, the sensitivity is 39.5, the quenching time is less than 1.7 s and the recovery time is less than 5.0 s indicating the potential for the formation of oxygen sensing material or device. Compared with conventional oxygen sensing materials used polymers or silicones as matrix, the sensing properties used MCM-41 as matrix have been improved because MCM-41 can enhance the effective collision between the diimine ruthenium complexes and oxygen quencher. Therefore, oxygen sensing materials with higher performance are obtained. In order to study further the effect of mesoporous molecular sieves on the sensing materials, we have designed and synthesized two metalloporphyrins, PtTPyP and PtTMPyP4+, as sensing molecules and incorporated them into MCM-41 to fabricate materials with oxygen sensing properties. The performance of PtTMPyP4+/ MCM-41 is better than that of the other one, the sensitivity is 55.5, the quenching time is 0.33 s and the recovery time is 26.62 s. The same luminescent sensing molecule, PtTPyP, used MCM-48 as matrix instead of MCM-41 to form sensing material. Through the comparison between PtTPyP/MCM-41 and PtTPyP/MCM-48, it is shown that the sensitivity and respond time of the latter are higher than that of the former because the three-dimensional pore structure of MCM-48 benefit for the gas transition without barrier. The results indicated that controlling the structure of matrix would improve the performance of sensing materials. The research of metal ion sensing materials is focused on the field that the effect of luminescence of the sensing molecule with different metal ions. But for most metal ion sensing molecules, the poor hydrophlicity of the organic sensing molecules doesn't benefit for the examination of the metal ions in water solution. We increased the hydrophlicity of the sensing materials by using MCM-41 as matrix with hydrophilic hydroxyl on the surface. And the metal ions in solution can be absorbed by MCM-41 for its pore structure that will enhance the sensitivity of the sensing materials for low concentration metal ion. The sensing material constituted of TTMAPP as luminescent molecule and MCM-41 as matrix. Emission spectrum study revealed that zinc (II) cation and copper (II) cation caused different luminescence changes of TTMAPP/MCM-41 even when the metal ion concentration was very low. It is much important for the development of metal ion sensing materials that the sensitivity is high for low concentration metal ions. We have also synthesized a quinacridone derivative with long alkyl chains, BEDAHQA, and used MCM-41 to improve the hydrophlicity of BEDAHQA/ MCM-41, which exhibits high luminescent property in solid state. Because of the ethylenediamine groups on the side chain of BEDAHQA, there is no direct interaction between the chelating group and the fluorophore, which avoids pH sensing. The luminescence of BEDAHQA/MCM-41 could be changed by the metal ions, especially when low concentration cobalt (II) cations existed, the...