| Organic luminescent materials have been widely used in optoelectronic devices due to their high quantum yield,amenable to optimization and excellent biocompatibility.Among them,single-benzene materials have attracted much attention because of their simple structure,easy modification,synthesis and purification.However,the development of single-benzene luminescent materials also faces two huge challenges: first,the skeleton of single-benzene is too small to achieve emission of different wavelengths,especially long wavelengths,so as to achieve full-color emission;second,such a mini-π system usually means a small radiation rate,so it would be a great challenge to improve its fluorescence quantum efficiency and realize excellent fluorescence emission.At the same time,traditional organic crystals are easy to split or fracture under the action of external forces,which immensely limits their application in actual production and life.Therefore,it is of great significance to design and synthesize new flexible organic crystals.In this paper,based on the structure of tetrasubstituted single-benzene,a series of organic single-benzene luminescent materials with different luminescence colors and different flexible properties were designed and synthesized.By modifying the substituent groups to regulate the molecular structure,firstly,we successfully realized elastic self-doping organic crystal.Secondly,the organic crystal can be freely bent and twisted to form a three-dimensional structure was attained.Finally,we reported self-doping organic crystals with size-dependent double mechanical bending(elasticity and plasticity)capabilities.The main content is as follows:1.In chapter II,we proposed a new strategy for the construction of full-color and highly emissive organic materials based on tetrasubstituted benzene,of which two electron-donating groups and two electron-withdrawing groups arranging in an X-shaped fashion.Firstly,by modifying different electron-donating and electron-withdrawing groups,we synthesized a series of organic single-benzene materials.They all have high fluorescence quantum yields.The emission color in the solid state can be adjusted from deep blue to red,achieving full-color emission.Secondly,we explained the reason of high efficiency and different emission wavelengths of the above materials through theoretical calculation and structural characterization of these compounds.And then we provided a method to regulate the luminescence of single-benzene material by modifying the donor and acceptor structure.Finally,we explore the application of these compounds as organic laser medium in the solid state.The results show that the compounds have good amplified spontaneous emission properties and can be applied in practice.Therefore,in this chapter,we not only proposed a new strategy but also highlighted the development potential and research value of the unique single-benzene structure.2,In chapter III,according to the work in the previous chapter,the first doped organic single crystal 1d@2d with elastic bending ability was designed and synthesized by introducing the electron-donating group of octylalkylamine into the X-shaped tetrasubstituted benzene structure.Firstly,through the “self-doping” method,we combined the host crystal 1d which is easily crystalized but non-fluorescent with the guest crystal 2d which has poor crystallization but is highly emissive.And then we obtained the doped emissive crystals 1d@2d with high quality and large size,integrating the advantages of both 1d and 2d.Significantly,the crystal has good elasticity.Secondly,we got deep insights into the “self-doping” and elastic mechanism from the crystal structure.In order to verify the conclusion,we introduced alkyl amine donating groups with different length carbon chains to synthesize a series of compounds 1a–c and 2a–c and investigated their crystal structures respectively.Finally,we studied their potential optical applications on account of that the doped crystal with high quality and large size are elastic and high emissive.The experiments show that the doped crystal displays good optical waveguide performance and amplified spontaneous emission property in both straight and bendable shape,making it possible for the application in flexible devices.3.In chapter IV,on the premise that elasticity has been achieved based on the tetrasubstituted single-benzene,changing the electron-donating group to an amino group,we reported the crystal DMDAT displaying not only elastic bending ability but also elastic twisting ability under applied stress.Firstly,we obtained the ribbon-like crystal DMDAT with high efficiency by controlling the crystal growth process.Meanwhile,the elastic bending of the crystal can occur in two directions respectively or simultaneously.What’s more,the crystal can be stretched into a three-dimensional structure by free bending or twisting.Secondly,we investigated its crystal structure to explain the mechanism of its free elasticity.Finally,the one-dimensional and two-dimensional optical waveguide were both realized due to the good quality,large size and efficient emissive of the ribbon-like crystal.Meaningfully,we ultimately achieved three-dimensional optical waveguide through constructing a one-dimensional crystal DMDTA with a three-dimensional stretching structure,making it possible for the use of fully flexible devices.4.In chapter V,we synthesized an X-shaped tetrasubtituted single-benzene luminescent material DMPAP with a amyl alkylamine group.It is a “self-doping”organic crystal with double mechanical bending ability.Firstly,we got crystals DMPAP of different sizes with high quality and efficient emissive through the“self-doping” method mentioned in chapter III.The crystal can not only undergo elastic bending,but also undergo plastic bending due to molecular layer slip when the elastic limit is exceeded.Secondly,we found that the mechanism of the elasticity of thin crystals by the analysis of its crystal structure.Finally,it is demonstrated that the crystals exhibited optical waveguide property not only in straight shape,elastic bending shape and plastic bending shape,but also in large two-dimensional crystals.On account of the anisotropy of crystal packing,it shows directivity of the optical waveguide in large two-dimensional crystals,showing the infinite potential of organic crystals in new optoelectronics fields in the future.To sum up,we designed and synthesized a series of single-benzene luminescent materials based on the X-shaped tetrasubstituted benzene structure.They are simple in structure,easy to synthesis and have excellent crystallization.They also have remarkable fluorescence quantum yields,exceptional physical properties and special mechanical properties,being excellent organic luminescent materials.Besides,we revealed the relationship between the microscopic molecular structure and the macroscopic performance,emphasizing the advantages of single-benzene luminescent materials and promoting the development of single-benzene luminescent materials.More importantly,this paper provided theoretical basis and application prospect of single-benzene materials in the future. |
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