Design,Synthesis And Photoelectric Properties Of Fluorenyl Strained Triangle Windmill-type Gridarenes

Steric design is an independent direction for the innovation of organic semiconductors beyond the donor-acceptor approaches.Until now,the typical steric design includes steric hindrance,strain,configuration,through space π-stacks as well as attractor-repulsor and so on.Under this background,it is significant to explore the design of the state-of-the-art steric complex systems that contain the multifactors such as both π-π stacks and strains,serving as the key scaffolds for the design of organic intelligent semiconductors to tune electronic,excitonic and ionic behaviors.Macrocycles are appealing building blocks for further systematic design by integrating not only the steric design but also the electronic design.However,most macrocycles have drawbacks in terms of the connectivity for the molecular architectures.Organic nanogrids are recently created by the vertical linkage of gridarenes,especially fluorene synthons,which possess the potentially extraordinary extendability,expandability as well as scalability.Under this circumstance,we combine strain and gridarenes,explore the new design of cross-scale molecular architecture,and design a series of strained triangle windmill-type gridarenes combining strain and π...π stacking.On the basis of the previous work of our research group,this paper studies the theory,synthesis,strain effects and aggregation effects of the strained triangle windmill-type gridarenes.The specific results are as follows.1.Combining the structural characteristics of the strained ring and the gridarenes,we design four strained triangular windmill-type gridarenes,namely fluorenyl triangle windmill-type gridarenes（TWG）,cyclopentadipyridine triangle windmill-type gridarenes（TWN）,cyclopentadithiophene triangle windmill-type gridarenes（TWC）and indenothiophene triangle windmill-type gridarenes（TWI）.Through Gauss View,Multiwfn and VMD software,their total molecular energy and strain energy,HOMO and LUMO electron cloud distribution,and weak intramolecular interaction are analyzed.It is found that TWG is the best synthetic target model for strained triangle windmill-type gridarenes.TWG has two diastereoisomers of cis-trans-TWG/cis-cis-TWG.The strain energies of cis-trans-TWG and cis-cis-TWG are 15.60 kcal/mol and 13.31 kcal/mol.In addition,compared with other reported strained rings,the strained energy of TWG is greater than that of square windmill-type gridarenes containing cyclopentadithiophene（SWGs-CPDT,5.52 kcal/mol）or fluorene（SWGs-F,8.1 kcal/mol）,tic-tac-toe-type nanogrids（TG,7.4 kcal/mol）,figure-8 shaped nanogrids（8G,5.8 kcal/mol）and [18] CPP（5 kcal/mol）,but less than [12] CPP（28 kcal）/mol).2.Based on the previous work of our research group,in the work of this chapter,we successfully synthesize TWG with a 35% yield through C-H bond activation reaction of 2-bromo-9-aryl-9H-fluorene with diastereoselectivity of cis-trans-TWG/cis-cis-TWG（80:20）.During the C-H bond activation reaction,we find that the palladium catalyst and PPh3 play an important role in the diastereoselectivity of TWG.To verify this phenomenon,we calculate TWG-TS1 and TWG-TS2,which proves that TWG-TS2 is more stable than TWG-TS1.Because the benzene at the 9-position of the fluorenyl group has a π···π interaction with the benzene of PPh3 for TWG-TS2,it is easier to generate cis-trans-TWG.At the same time,the structures of cis-trans-TWG and cis-cis-TWG were further confirmed by HRMS,MALDI-TOF-MS,¹H NMR and single crystal XRD diffraction.3.In the work of this chapter,we analyze the structural characteristics of cis-trans-TWG/ cis-cis-TWG.The structural characteristics mainly include weak intramolecular interaction and strain through single crystal and theoretical calculation.It is found that both cis-trans-TWG and cis-cis-TWG have delta-stacked π···π repulsive intraactions.The angle strain and bending strain of cis-trans-TWG are not much different from those of cis-cis-TWG,and torsional strain of cis-trans-TWG is much greater than that of cis-cis-TWG.Through the analysis of time-dependent density functional theory（TDDFT）simulation and experimental PL spectra of cis-trans-TWG and cis-cis-TWG,we find that the PL spectrum of cis-trans-TWG（348 nm）have a red shift of 25 nm than the spectrum of cis-cis-TWG（323 nm）.And compared with the 0-0 transition peak of dimeric molecule 3,the PL spectra of cis-cis-TWG and cis-trans-TWG have red shifts of 12 nm and 37 nm,respectively.These results indicate that TWG exhibits strain-induced photophysical properties.In addition,in the UV absorption spectra and PL spectra of cis-trans-TWG(10^-5 mg/m L-10^-1 mg/m L),the peak basically remains unchanged as the concentration increases.O nly when it increases to 10-1 mg/m L,there are obvious red shifts of 22 nm and 18.5 nm,respectively.These results indicate that the process involves the mechanism of aggregation-induced emission.