Professor Xie Linghai, Nanjing University of Posts and Telecommunications Research Group: build multi-level ordered structure through stereoisomerization strategy to improve the stability and efficiency of blue light emission

The stereoisomeric effect of lead organic molecules is a hot topic in the field of materials science and chemistry It is the key factor to precisely adjust the molecular arrangement, control the self-assembly behavior of molecules and optimize the condensed structure Recently, Professor Xie Linghai, School of materials science and engineering, Nanjing University of Posts and Telecommunications By controlling the stereoisomerization of the molecules, the racemate of the broad band gap blue light molecule fluorene alcohol (2o8-dpfoh-sfx) has been successfully introduced into the hierarchical ordered crystal structure The ordered supramolecular framework shows extraordinary crystal enhanced emission and excellent spectral stability, which is not achieved by the internal racemate So far, the macropositive effect of the non enantiomer has been found Relevant results were published online in chem (DOI: 10.1016 / j.champr 2019.06.021) Professor Xie Linghai's research group is based on the information materials and Nanotechnology Research Institute (IAM) of Nanjing University of Posts and telecommunications and the National Key Laboratory of organic electronics and information display, led by academician Huang Wei Since then, we have been carrying out scientific research and innovation with molecular system and mechanical parts as the central axis, involving such cutting-edge interdisciplinary directions as organic electronics, neural morphological computing, artificial intelligence chemistry and gefluorene intelligent machine At present, it has made progress and formed a foundation in the fields of organic wide band gap semiconductor chemistry, efficient and stable blue light emitting and laser materials, organic nanocrystals and their green manufacturing, organic data storage and memristor The research group has published more than 230 papers in internationally renowned academic journals, including Chem, NAT Commun., adv mater., J am Chem SOC And other internationally renowned journals In the past, the research group has trained a group of outstanding young scholars, overseas doctors, research and development engineers in the fields of OLED semiconductor chips and drugs At present, there are 6 young teachers, 1 postdoctoral, 5 doctors and 30 masters Prof Xie Linghai Xie Linghai graduated from Fudan University in 2006 with a doctor's degree from academician Huang Wei Now, he is the vice president of the Institute of materials science and Engineering (IAM) of Nanjing University of Posts and telecommunications, the leader of chemistry discipline, the director, professor and doctoral supervisor of the center for molecular systems and organic devices (CMS OD); he is the new century talent of the Ministry of Education, the winner of the National Excellent Youth Fund, and the leader of the "six talent peaks" of Jiangsu Province The innovative talents team and the excellent scientific and technological innovation team leaders of Jiangsu colleges and universities enjoy the special allowance of the government of the State Council He has been engaged in the research of organic wide band gap semiconductors for a long time, and his main contributions include the one pot method of spiro aromatics, the theory of molecular absorption and repulsion coordination (SMART), organic nanolattices and their nano polymers, and molecular multimedia semiconductors Currently, as a writer or corresponding author, he has worked in Chem, NAT Commun., adv mater., J am Chem SOC, More than 150 SCI papers have been published in prog.polymer.sci.and other magazines, all of which have been cited for more than 4500 times, with H-index of 39, 5 Monographs (chapters) written, more than 20 invention patents authorized, more than 10 national and provincial scientific research projects presided over, and won the second prize of National Natural science There are three prizes (ranking the third), the first prize (ranking the second), the second prize (ranking the third and the fourth), the first prize (ranking the second), the 13th "Challenge Cup" National College Students' extracurricular academic and technological works competition excellent instructor award Cutting edge scientific research achievements: in nature, it is an effective strategy to precisely control the stereochemistry of organic molecules to achieve mechanical flexibility, self-healing and intelligent materials by building multi-level ordered structure through stereoisomerization strategy and improving the stability and efficiency of blue light emission Relatively ordered molecular stereoisomers, such as isotactic or syndiotactic isomers, can usually induce regular molecular packing and thus exhibit excellent macroscopic properties in condensed structure Stereoisomers in organic semiconductors, including CIS and trans isomers, enantiomers and chiral compounds, have been widely concerned in the field of Organic Optoelectronics in recent years, but their main purpose is to achieve unique photophysical properties, especially chiral behavior, polarized emission and light detection/ However, few attention has been paid to the use of isomerization to precisely control the structure and morphology of graded and ordered condensed matter Stereoisomerism with stereoregular configuration is expected to have a profound impact on orientation conformation, ordered molecular accumulation and chemical and physical properties, so that stereoisomerism becomes a molecular platform to achieve hierarchical ordered condensed structure Fluorene derivatives have been widely studied due to their deep blue light emission and high photoluminescence quantum efficiency As a functional site, fluorene 9-position chiral SP 3 carbon is an active site for the preparation of various stereoisomers, the regulation of photoelectric structure and the control of molecular arrangement In this work, the author designed and synthesized the supermolecular oligofluorenol 2o8-dpfoh-sfx of spirofluoreoxyanthracene (SFX) according to the principle of synergetic molecular attractor repulsor theory (SMART), and connected a benzene ring and hydroxyl group on its chiral SP 3 carbon (Fig 1) As expected, the molecule shows different stereoisomers: racemate and racemate, further showing different conformation and self-assembly behavior, as well as photoelectric properties Figure 1 Two stereoisomers of hydrogen bonded sterically hindered supramolecular oligofluorenol: racemate and racemate (source: Chem) The author first studied the effect of stereoisomerism on the construction of ordered crystal structure Rac-2o8-dpfoh-sfx was dissolved in toluene solution After a simple aging process, the solution changed from clear to turbid Under the irradiation of 365nm ultraviolet lamp, the color changed from dark blue to sky blue Take a little solution from the pipette gun and drop it on the silicon wafer to dry for observation, then regular rectangular nano wafer can be obtained (Fig 2) SEM, TEM and AFM show that the length, width and thickness of the nanocomposites are about 7 μ m, 3 μ m and 160 nm respectively Then, the crystallinity and crystal surface of the nanocomposites were characterized by saed, XRD and GIXD The results show that the Nanoflake is a layered structure, lying on the substrate with (001) surface as the support surface, and the phospholipid like bimolecular layer interleaved stacking mode (ILB) is adopted Under the same preparation conditions, the toluene solution drop film of meso-2o8-dpfoh-sfx can only obtain continuous films without regular nanostructures It can be seen that the self-assembly behavior of the two stereoisomers is obviously different Fig 2 The morphological characterization of rac-2o8-dpfoh-sfx and the interpenetrating stacking mode of phospholipid like bimolecular layer (source: Chem) were further studied by the authors (Fig 3) It was found that the absorption spectrum of racemic annealed film and nano film showed a shoulder peak at 402 nm, similar to that of polyfluorene β Compared with the initial spin coating film, the emission spectrum of the characteristic peak of the conformation has a significant red shift, indicating that it is a planar conformation However, when the annealing temperature of the racemate film is changed from 130 ° C to 250 ° C, the absorption spectrum of the racemate film does not change and there is no conformational change The generation of coplanar structure in racemates was further verified by the excitation and emission spectra at low temperature We also use the time-domain fluorescence lifetime imaging microscope (FLIM) to study the change of the average fluorescence lifetime of different conformations It is found that the exciton in the planarized conformation decays faster than the random conformation, resulting in a significant reduction of the fluorescence lifetime Fluorescence anisotropic imaging microscope (FAIM ）The results show that the anisotropy of the inner racemate film is low before and after annealing, the image morphology is uniform and narrow, it is amorphous, and energy transfer will lead to significant loss of emission polarization; while in the outer racemate, the formation of coplanar conformation leads to significant differences in the anisotropy: the initial film anisotropy is low, and the overall anisotropy is different after thermal annealing The distribution was wide Fig 3 Optical properties of rac-2o8-dpfoh-sfx in different states (source: Chem) The author further found that compared with the emission of aggregation induced quenching (ACQ) in traditional trimer, the nano film and annealed film of rac-2o8-dpfoh-sfx showed abnormal crystal enhanced luminescence, and the plqe of nano film increased to 65% , up 90% In addition, the racemic films annealed in nitrogen have no obvious green band emission, which shows that they have good spectral stability Similar to the molecular encapsulation strategy, the structural rigidity, dense packing and ordered conformation of crystal structure can lead to excellent morphology stability (limiting molecular movement) and chemical oxidation resistance (effectively preventing the permeation and diffusion of H 2O / O 2) In order to further study the luminescent properties of films and crystals, the stimulated radiation properties of two stereoisomers in different film states were studied The ASE peak of the annealed rac-2o8-dpfoh-sfx film redshifts to 445 nm, which corresponds to the 0-1 transition of the fluorescence emission spectrum of the planarized conformation The laser oscillation behavior of the racemic nano sheet can be directly observed under the excitation of the optically pumped laser (Fig 4) Figure 4 Crystal enhanced emission and spectral stability of rac-2o8-dpfoh-sfx crystal superstructure (source: Chem) In conclusion, the author systematically studied the effect of stereoisomerism on molecular orientation and crystallization behavior The centrosymmetric configuration of rac-2o8-dpfoh-sfx enables the molecules to self assemble to form a hydrogen bond assisted supramolecular crystal framework and stabilize their planar conformation Compared with meso-2o8-dpfoh-sfx, the hierarchical and ordered aggregation of racemic annealed films and nano film results in higher fluorescence anisotropy Fluorescence lifetime imaging also shows that the main chain structure of the plane has a shorter lifetime compared with the random phase Different from the traditional conjugated molecules, the crystal structure shows abnormal super stable crystal enhanced luminescence (plqe up to 65%) In order to further verify the effect of the planarized conformation on the properties of the material, we have realized the deep blue laser behavior of the racemic nano wafer The emission peak is located at 447 nm, which corresponds to the 0-1 transition of the fluorescence emission spectrum of the planarized conformation This is the first report on the influence of molecular diastereomer on the structure and photoelectric properties of graded condensed matter This work proves that the chirality diversity and its effect are potential factors that can not be ignored, and provides a basis and new idea for the study of the aggregation structure in organic semiconductor materials science by using chirality strategy The research results were recently published in chem (CHEM, 2019, DOI: 10.1016 / j.champr 2019.06.021) Academician Huang Wei of Northwest Polytechnic University and Associate Professor Lin Jinyi of Nanjing Polytechnic University are the co correspondents of the paper Yu Mengna, a doctoral candidate in school of materials science and engineering of Nanjing University of Posts and telecommunications, is the first author of the paper The research work has been supported by NSFC, national major basic plan integration, Jiangsu "six talent peaks" and other projects Nowadays, people and scientific research have been paid more and more attention in the economic life China has ushered in the "node of science and technology explosion" Behind the progress of science and technology is the work of countless scientists In Chemistry