Design,Synthesis,Self-assembly And Crystal Luminescence Stability Enhancement Of SFDBA And Its Derivatives

As typical organic wide band gap semiconductors,fluorene-based materials are more flexible in functionalization at 9-position than benzene.The design of bulky fluorenes is an ideal model to determine the complex interactions of bulks and to gain a deep understanding of the effects on exciton,mobility and stability.Among them,spirocyclic aromatic hydrocarbons(SAHs)have wide applications in the field of organic optoelectronics due to their unique orthogonal rigid framework,steric hindrance,conjugation-interrupted spiroconjuntion effect,good thermal stability and color stability.At present,there are many reports on the synthesis of SAHs.However,there are still some deficiencies in reducing the synthesis steps,increasing the total yield and obtaining more new functional derivatives,and new simple synthesis methods still need to be developed.On the other hand,in previous work,we have found that SAHs tend to self-assemble into three-dimensional polyhedral structures,and the low-dimensional micro/nano structures obtained are based on the strategy of using planar conjugated fragments to modify SAHs.Can SAHs self-assemble into low-dimensional structure and the formation mechanism are still unknown issues.Furthermore,the defects caused by the instability of spiro plane in SAHs have not been solved.In response to above problems,we developed a new synthesis method of SAHs derivatives,realized low-dimensional morphology of SAHs by reprecipitation method and explained the structure-activity relationship.Finally,based on model molecule SFDBA,the effect of different aggregation states on photooxidation was explored,and a new strategy for crystallization to improve photochemical stability was proposed.1.Based on the classic Ullmann reaction,the carbazole-substituted SFDBA and SFDBAO derivatives were effectively synthesized.The heteroatom and carbonyl moieties on SAHs act as reaction guide groups and induce the remote C-H bond activation.Compared with the previous C-H bond activation reaction,this method has several major advantages:(1)Provide a series of SAH derivatives with good yield and excellent chemical selectivity;(2)Different from most C-H bond activation reactions,direct arylation of C-H coupling involves fewer steps,lower costs,fewer toxic reagents and higher atom economy,and the reaction conditions are easier to achieve;(3)The particularity of the reaction sites,there is the remote induction of the guiding group.This synthesis reaction will provide a flexible way to produce various SAH derivatives without harsh conditions,toxic reagents and precious metals.Moreover,these carbazole-substituted derivatives exhibit as a donor-acceptor-donor(D-A-D)model,which have potential application prospects in the field of optoelectronics.2.Two typical SAHs derivatives SFDBA and SFDBX were used as models to explore whether SAHs can form low-dimensional structures and their structure-activity relationships,and further explored the photophysical behavior of the two compounds under diverse aggregation states.The belt-like one-dimensional structures of two compounds were obtained without adding any surfactants.As the supramolecular interaction sites are concentrated on the heterocyclic planes,HAPs are arranged with each other in the middle,and FPs on the two sides to form an independent interdigital layer standing on the(100)plane.Due to the weak van de Waals forces along a-axis,the growth rate in this direction is suppressed and finally leads to a layer-by-layer low-dimensional structure.This work testified SSH effects are no longer limited to SAHs containing substituents,but can be modified under different scales.Our well-distributed structures in crystalline states of both compounds exhibit prominent crystalline-enhanced emission.3.A new strategy to improve the crystalline photooxidation stability was proposed and verified by model molecule SFDBA.Time-resolved photooxidation experiments of SFDBA in different aggregation states were designed,subsequent model analysis and spectral characterization were carried out to propose and verify the crystallization stability enhancement strategy.The experimental results show that as the degree of aggregation and periodic array increases,the rate of photooxidation has a significant decreased,and it takes longer to deteriorate.In particular,steric hindrance part form an“armor”layer to protect fragile and self-sensitive units in the layer,can effectively obstruct O₂ infiltration,dramatically enhanced their photophysical constancy.Crystallization has become another new tactic for photochemistry stability elevation:(1)The stable steric hindrance frame forms firm“armor”layers;(2)Orderly accumulation after crystallization shelter the vulnerable units in the“armors”.This crystallization strategy allows susceptible molecules to defend themselves through aggregation without resorting to other external conditions,leading to excellent photophysical properties and stability,which is significant for constructing stable and durable optoelectronic devices.