| Organic optoelectronic materials have potential applications in display,storage,detection,etc.,of which organic single crystals with long-range ordered structures are considered to be the most ideal choice to reflect the intrinsic properties and build electronic devices with high performance.However,compared with inorganic crystals,the development of organic crystals is still at an early stage.Research on related crystallization mechanisms,polymorphic phase transitions,and growth methods is far from systematic.Therefore,only when these intrinsic scientific problems were understood can organic optoelectronic crystal step into the practical stageTo fundamentally improve the photoelectric performance,we should establish the relationship between the crystal structure and the properties.On the one hand,we can introduce specific substituents to adjust performance by molecular design.The way of changing the structure generally requires redundant chemical synthesis.On the other hand,we can easily adjust the performance by changing the aggregation state based on the same molecule.This approach refers to the classic problems of polymorphism and phase transitions.How molecules crystallize into polymorphs,the specific conditions for phase transitions between polymorphs,and the mechanism of phase transitions are urgent problems to be solved.Especially for the phase transition processes in the solid state,it is difficult to track the details of the interface changes by conventional X-ray diffraction and other spectroscopy methods.Thus,most of the phase transition mechanisms have not been explained clearly.To solve these problems will help us better regulate the material properties and give play to the advantages of optoelectronic crystals in practical applicationsTwo-dimensional organic crystals have inherent advantages in organic optoelectronic devices and are expected to truly realize the application of large-area flexible electronic devices.However,the large-area two-dimensional crystal fabrication technology has not a substantial breakthrough so far.On the one hand,most organic crystals have poor crystallinity for weak intermolecular van der Waals forces.On the other hand,organic crystal growth methods are usually based on the solution method and the physical vapor transport method,which are both spontaneous growth and have poor controllability for materials that tend to grow into three-dimensional organic crystals.In addition,the current organic single crystal growth method is only suitable for growing a small number of crystals to verify the intrinsic of the material.Therefore,it is necessary to develop anew high-throughput growth method to meet the application requirements of optoelectronic devices for organic crystals,especially two-dimensional semiconductor crystals.To sum up,we take high-performance organic single crystals as the research goal,and have an in-depth discussion of the photoelectric properties of organic single crystals Then we emphatically studied the basic problems in the process of organic polymorphism and phase transition.On this basis,a large-area two-dimensional organic semiconductor growth method was further put forward.The main research contents are as follows:1.Three compounds 1DQCN,2DQCN and 3DQCN with aggregated fluorescence enhancement characteristics were designed and synthesized by introducing a tetraphenylethylene twisted skeleton and the dicyanopyrazine group.By analyzing the molecular stacking modes of these compounds in different aggregated states,a deep-level relationship between aggregated state structure and mechanical force-emission properties was established,breaking the traditional phenomenon of mechanical force-induced emission redshift and crystallization-induced emission blueshift.The conclusion provides theoretical guidance help us understand,design,and regulate the properties of materials from the perspective of chemical structure and molecular accumulation.2.The polymorphism and phase transition of 2DQCN and its application in the detection of volatiles are discussed in depth.By controlling the growth conditions,red crystal phase,orange crystal phase,and yellow amorphous phase with distinct emission wavelengths can be generated.Through different heat and solvent stimuli,these polymorphs can be quickly switched.2DQCN can be used as a visual probe to detect volatile organic compounds(VOCs)with high sensitivity and selectivity This intuitional vision sensor has immeasurable application value in the detection of automobile exhaust and industrial emissions.3.In situ microscopic observation of the single crystal to single crystal phase transition process of 3DQCN by fluorescence/polarization switching.The transformation rule of the phase change interface was analyzed using the photoelectric signal of the organic molecule itself.The retention of the molecular layer and the orientation movement of the interface were reasonably determined to avoid lattice collapse The micro/nano scale structure analysis revealed that the crystal phase transition mechanism is "nucleation-growth".This work has important significance in studying the mechanism of organic crystal growth and phase transition.4.The confined flux growth of large-area two-dimensional organic semiconductor single crystals was developed.Innovative introduction of polydimethylsiloxane as flux,dispersant and protectant.The growth mechanism and applicability of the confined flux growth were studied.The crystals can be directly integrated on the substrate or made by inkjet printing.The confined space in the Z direction allows crystals that have two-dimensional growth characteristics.This method is universal,that can grow high-quality crystals for more than a dozen organic semiconductor materials that have been tried so far.This method has the following characteristics with no need for vacuum,high raw material utilization,low cost,easy operation,and fast speed. |
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