Design,Synthesis And Properties Of Novel Photoswitchable Molecules

Photoswitchable molecules has been used in many fields such as instant image,data storage,and molecular machines for their reversible photo-induced transformation between two or more isomers.The photoisomerization mechanism of the well-developed photoswitches includes trans-cis isomerization,pericyclic ring-opening and ring closing reaction,heterolytic bond break and formation and homolytic bond break and formation(HBBF).Among them,the strategy based on light or thermal induced reversible HBBF is less investigated.Recently,our group has developed a novel class of chiral photoswitchable molecule named cyclopentadienone dimer(CPDdimer)based on HBBF mechanism.This dissertation is focused on the design,synthesis and characterization of CPDdimer derivatives.This dissertation is targeted at revealing the relationship between structure and photoswitching properties of CPDdimer derivatives and providing novel photoswitches with widely tunable properties.The first part is mainly focused on the chemical modifications of CPDdimers.We develop two feasible strategies to derive CPDdimer and receive 7 CPDdimer derivatives in total.One of the strategies is to introduce bromine into the precursor,and the following cascade reaction provides two dibrominated CPDdimers.In order to investigate the effect of substituents on photoswitching properties of CPDdimer,one of dibrominated CPDdimer are used as an example to be further functionalized with different aromatic compounds.The other method is to introduced malononitrile at the carbonyl of cyclopentadienone.The structure of the two dibrominated CPDdimers are confirmed by single-crystal X-ray analysis.All new compounds are characterized by nuclear magnetic resonance and high-resolution mass spectra.This work provides two dibrominated CPDdimers that can be used as precursors for on-demand functionalization.Furthermore,CPDdimer derivatives enrich the molecular library for the study of photo switching properties and applications.In the second part,we systematically investigate the impacts of substit uents on photoswitching properties of CPDdimer derivatives through absorption spectra,cyclic voltammograms,NMR and so on.The substituents on naphthalene ring could effectively modulate the absorption spectra and HOMO-LUMO energy gaps of CPDdimer derivatives.On the other hand,the steric hindrance effect of substituents increases the length of C-C single bonds linking two cyclopentadienone derivatives in CPDdimer derivatives,resulting in the decrease of their thermal isomerization activation energies compared with pristine CPDdimer.In this part,we have proved that the properties of CPDdimer can be widely tuned by the substituents.The length of C-C single bonds linking two cyclopentadienone derivatives in CPDdimers plays a key role in the reverse thermal isomerization.The third part summarizes the research work at the beginning of my master degree.We incorporate heterocyclic aromatic rings into imide-fused corannulene and investigate its influence on properties of corannulene.Diindole-fused corannulene imide are synthesized through two steps,Suzuki coupling and subsequent reductive cyclization reaction.Fusing indole rings into corannulene imide leads to significantly red-shifted absorption,a lower HOMO-LOMO band gap,and a lower bowl-to-bow inversion barrier than those of corannulene imide.The heterocycle also decreased the aromaticity of the rings of corannulene moiety adjacent to heterocycles.This work provides a straightforward strategy to enrich the molecular library of heterocyclic compounds annulated corannulene and also presents a potential n-channel semiconductor.