Construction Of π-Gels With Controllable Fluorescence Emission

Recently,π-conjugated organogels have attracted considerable attentions in the supremolecular chemistry, because of their unique self-assembly structures and controllable optoelectronic properties.π-Conjugated organogelators can self-assemble into various dimensional and morphologic superstructures in organic solvents directed by noncovalent interactions such as H-bonding, vander Walls,π-πstacking ect. The supramolecular self-assembly ofπ-conjugated organogelors can attribute many new features beyond the single molecules. Meanwhile,π-conjugated organogelators could be selectively functionalized with the introduction of desired moieties so as to build up target system with various properties, which possess specific applications in light harvesting, energy and charge transfer, and switches.Herein, we have designed and synthesized a series of carbazole-based and phenothiazine-based organogelators, which can self-assembled into well-orderedπ-gels with controllable fluorescence emission. In order to mimic the natural light-harvesting system, diaryldiketopyrrolopyrrole and perylene-carboxylic diimides derivative were introduced into the obtained carbazole-based organogels. Some creative results have been obtained, and the main points are outlined below:(1) A series of carbazole derivatives were synthesized and their self-assembling as well as photophysical properties were investigated. It was found that the monomeric and dimeric carbazoles containing tert-butyl groups could gelatize some organic solvents, but the ones without tert-butyl groups could not form organogels, indicating that the tert-butyl unit plays a key role in the formation of the organogels. We suggested that the large spatial effect can enlarge the distance between aromatic moieties and weaken theπ-πinteraction between carbazoles, which may balance the solubility and deposition to lead to the formation of the gel. Based on the results of IR, UV-Vis and XRD, the possible molecular packing model was proposed. It is worth noting that the aggregation-induced-emission was detected during the process of gelation, which could be ascribed to a combination of the formation of J-aggregate, enhancement of planarization and the restriction of rotation of single bond in the chromophores. This work supplies a new way to design novel functional soft materials by controlling the intermolecular interaction.(2) We firstly synthesized rigid dendritic gelators based on oligocarbazoles, and the influence of the generation of dendron on their gelation ability was investigted. It was found that second generation of carbazole dendron could form gel by ultrasonic stimulus, and the obtained gel can emit strong blue-green light. The first generation of carbazole dendron can only form two-component gel assisted by 1,6-hexamethylenediamine, and the obtained gel can emit strong blue light. The third generation of carbazole dendron can not gelatinize any solvents owing to special spatial conformation.(3) We generated well-ordered 1D arrays based on carbazole and diaryldiketopyrrolopyrrole derivatives in order to mimic the natural light-harvesting system, in which carbazole-based organogel was used as a scaffold to make diaryldiketopyrrolopyrrole grow up along the gel fibers. In the composite gel, partial excitation energy transfer from carbazole-based organogelator, the light-harvesting antenna, to the diaryldiketopyrrolopyrrole derivatives, the acceptor, occurred. Notably, the composite gel could emit intense red light or purplish white light by tuning the excitation wavelength. It provided a simple way to fabricate functional supramolecular arrays. Such ordered soft materials with various emitting colors may have potential applications in sensor and photonic devices.(4) A white-light-emitting organogel system based on rigid dendritic carbazole-based gelator and diaryldiketopyrrolopyrrole derivatives was fabricated. In the composite gel, partial excitation energy transfer occurred from energy donor of carbazole-based organogelator with bluish green emission, to the diaryldiketopyrrolopyrrole derivatives, the acceptor, with red emission, leading to a white-light-emitting organogel. The energy transfer efficiency could be tuned by adjusting the intermolecular interaction between energy donor and acceptor, which provided a simple way to fabricate white-light-emitting soft material.(5) Phenothiazine and carbazole derivatives were synthesized, and their gelation ability and photophysical properties were investigated. It was found that phenothiazine formamide derivative with long carbon chain can gelatinize n-henxane, cyclohexane and enthanol/water by untrasonic stimulus. Notably, compared to the solution, the fluorescence emission of the gel phase bule shifted significantly, which were attributed to the suppression of TICT. Such functional soft material may possess potential applications in sensors.