| Due to their unique electronic structure and excellent optoelectronic properties, siloles have attracted more and more attention among numerous areas such as photoelectric materials, chemo-sensing, bio-detection and imaging, and smart materials, making the design and development of functional siloles with novel properties become an important issue in the fields of organic synthesis and materials. They are of great significance both in the theoretical research and real-world applications of organic semiconductors.The improvement of synthesis methods and the investigation on structure-property relationship as well as the expansion of their applications are the key points of the exploring of novel silole systems. Exploiting of silole as a platform for functional siloles is a fundamental strategy to figure out these problems but at the meantime itself is a challenge. Owing to the incompatibility between polar groups and catalysts used in silole preparation, polar or active functional groups are hard to be incorporated into silole systems. Among the existed siloles, functional siloles are numbered and the ones can be used as modification platforms are very rare. In this paper, we take this challenge. Through the protection and in-situ deprotection of aldehyde group, we successfully synthesized two siloles functionalized with aldehyde group and by taking advantage of their polyreactivity, several other siloles were further prepared and the long-wavelength emission of silole has been achieved. Utilizing the specific reaction between these functional siloles and some particular amino acids, we constructed efficient biosensors. Meanwhile, through systematic investigation of the molecular structure and electronic structure of these functional siloles, and their properties such as photo-physical, thermal, electro-chemical and electroluminescence properties, we gained a deep insight into the influence of the type and the position of these polar substituents on the properties of siloles.We firstly synthesized three novel functional silole derivatives symmetrically substituted on their2,5-positions with electron-accepting or donating moieties by means of modifying the classical Tamao procedure. A systematical study and comparative analysis of the structure and physicochemical properties provided a strong basis and effective guidance for follow-up study of functional siloles. The obtained functional siloles exhibit a typical aggregation-induced emission (AIE) or aggregation-enhanced emission (AEE) characteristics and unique solvatochromism as well as intriguing charge effect. Aldehyde-functionalized silole, i.e. DMTPS-ALD is an effective post-functionalization platform, and the DMTPS-DCV prepared from it is orange-red emissive. DMTPS-DPA is the first example that successfully transform an aggregation caused quenching (ACQ) fluorophore into an AEE active one with a silole molecule. It can not only act as a hole-transporting layer but also a light-emitting layer simultaneously, and the resulted device performance is comparable to or even better than the reported results of yellow light EL. These functional silole derivatives filled the blank of polar siloles and expanded the silole family.Secondly, carefully examined and summarized the previous works, we then found that the propeller-shaped AIE molecules have the great potential to be used as a building block to construct soft porous crystals (SPCs). Thus then we came up with a bran-new SPCs construction rationale which is distinctly different from the ones used to build the classic organic frameworks and metal-organic framework. We screened out the pure conjugated component possessing photoelectronic activities, i.e. DMTPS-DCV, to verify the above design concept, and the SPCs with outstanding performance were obtained. The softness of the resulted SPC is rendered by the intramolecular rotations between the multiple rigid aromatic substitutes and the conjugated core. Its porosity is intrinsically generated by the non-coplanar configuration of the extended rotatory aryl blocks and the long-range structural regularity is guaranteed by the dipole-dipole interactions between the polar groups of the building blocks. More importantly, the present SPC has demonstrated unique emission behavior that is acutely sensitive to environmental stimuli such as solvents, mechanical force and thermal treating. Conceiving the promising and interesting applications of the ordered frameworks with electronic-optical activities and structural transformability in chemical and biological sensing arrays, the present strategy to build up SPCs has great significance and is helpful to construct and develop novel organic porous materials with specific functions based on various conjugated building blocks.Thirdly, based on DMTPS-ALD, we developed a novel fluorescent (FL) probe, which utilizing the aldehyde groups as reactive functionalities and the AIE active DMTPS core as the signaling moiety. The probe exhibited excellent specificity and selectivity and its response was reflected in the enhancement of fluorescence, shift of emission peak and the precipitation of products. Due to the aldehyde functionalities, this specially designed probe can selectively react with Cys and Hey in distinct kinetics, which discriminated these two highly similar amino acids. GSH shows a significant quenching effect on the FL responses of the probe molecule to Cys or Hey and thus can be reversely detected. We set up an unprecedented strategy of using a single fluorescent probe to discriminately detect Cys, Hey and GSH by FL turn-on and turn-off strategies. The present strategy is intrinsically a fluorescent titration, which combines the high sensitivity of FL spectroscopy and the reliability of precipitate titration methodology. What’s more, the primary investigation of the FL response to deproteinized human plasma indicates that this FL probe is a promising one for the discriminatory detection of Cys on a clinical level.We used the AIE-active fluorogens (DMBFDPS and TPE-ALD) as a probe to detect Cys and Hey and verified that the above mentioned fluorescence titration method is a proof-of-concept study. The action principles for the present probes are consistent to be the precipitates (aggregation)-induced emission and the discriminatory detection of Cys over Hey depends on the kinetic difference. Moreover, the response behaviors of DMBFDPS and TPE-ALD to Cys in the deproteinized human plasma or biocompatible medium showed that their response point meets coincidently with the normal level of Cys in human plasma, which gives a clue that these two dialdehy-substituted AIE molecules could be applied as potential indicators of Cys deficiency. It’s worthy mentioning that although their response behaviors are largely the same, their detection performances is different. Thus we could come to the conclusion that the capability of discriminatorily detecting Cys over Hey is a common attribute to all the dialdehyde-functionalized AIE-active molecules and the response performance could be modulated by the molecular structures and the hydrophobicity.Finally, using DMBFDPS as an intermediate, we synthesized DMTPS-m-DCV and then carefully studied these two weto-functionalized siloles and their/rara-substituted isomers on their structure and physiochemical properties (crystal structure, electronic structure, thermal, AIE, solvatochromism properties and their emitting behaviors in their PMMA blended films) and further carried out a detailed comparative analysis of them. In general, by virtue of the difference in conjugation, the meta-substituted groups exert smaller impact on the parent silole compared to para-substitution. This work not only enlarged the family of polar siloles and perfect the silole systems but also provided a solid basis for the research and development of silole. In view of the reactivity between a,αxβ-unsaturated malononitrile and mercapto compound, the solution of DMTPS-DCV and DMTPS-m-DCV was spotted on the TLC plates to fabricate "fluorescent testing strips", which acted as very handy sensors to detect the mercapto compounds in organic solvents and showed different response behaviors due to the difference in the reactivity of the thiols and the solubilities of products. Compared with DMTPS-DCV, DMTPS-m-DCV is more reactive to thiols. In particular, the "testing strips" of DMTPS-m-DCV can readily respond to the Cys in water in1min and the response concentration is as low as0.0003mg mL-1. In addition, DMTPS-m-DCV possessed a very high specificity to Cys in aqueous solution but hardly showed any response to Hcy, in other words, DMTPS-m-DCV can discriminate Cys over Hey in water, indicating that it has great potential to be clinically used as an efficient fluorescent probe. |
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