Synthesis And Properties Of Stable Olympi-cenyl Radicals

The study of spin 1/2 open-shell graphene fragments（OGFs）with one unpaired electron offers opportunity to establish their well-defined structural property relation-ship,thus provides guidelines for designing stable OGFs with novel functionalities.However,spin 1/2 OGFs systems with one unpaired electron remain largely unexplored.The main problems are listed as follows:（1）It is difficult to synthesize and isolate the spin 1/2 OGFs compounds due to their intrinsic poor stability;（2）The lack of system-atic study for spin 1/2 OGFs system with variable size and shape in the current literature,with major focus on phenalenyl radical with three fused rings.Hence,exploration of new spin 1/2 OGFs is the key to promote the development of OGFs towards material application.In this thesis we focus on the synthesis and property of olympicenyl radical,which is a more complex spin 1/2 OGFs system with five fused rings.The second chapter introduces a kinetic protection strategy to synthesize two sta-ble olympicenyl radical derivatives,OR1 and OR2,protected with triisopropylsi-lylethynyl（TIPSE）.X-ray single crystal analysis disclosed unique 20-center-2-electronπ-dimer structure both for OR1 and OR2,indicating a negligible effect of bulky sub-stituents at 4,8 positions on theπ-dimerization.In addition,π-dimerization behavior both for OR1 and OR2 in solution state were systematically investigated by variable-temperature electron spin resonance（ESR）spectroscopy,UV-vis-NIR spectroscopy and cyclic voltammetry.Theoretical calculations by NICS_zz scan and ACID plot indi-cated thatπ-dimer showed an enhanced aromaticity compared with monoradical,re-vealing the essential reason for the formation ofπ-dimer.In the third chapter,the complicated stereochemistry and energetics ofσ-dimer of OR1（σ-OR1₂）were demonstrated by theoretical calculations,and the energetic pref-erence ofπ-dimer overσ-dimer was found.Next,E-biolympicenylidene derivative was isolated by treatment of the toluene solution of OR1 with p-chloranil,hence,theσ-dimerization of OR1 in solution was proved experimentally.Then,the single crystal structure and physical properties of E-biolympicenylidene were investigated in detail.Finally,the energy profile of electrocyclization pathway and the spin density at the bonding sites for radical-radical coupling pathway were investigated by theoretical cal-culation,which disclosed the reason for low reactivity towards ring-closing reaction of E-biolympicenylidene.In the last chapter,we developed a synthetic strategy to synthesize a series of 6-aryl-olympicene derivatives,which realized the synthesis of E-biolympicenylidene.Then,6-pentafluorophenyl-olympicenyl radical derivative（PFP-OR2）can be synthe-sized successfully after introducing substituents at 4-and 8-position.X-ray crystallo-graphic analysis indicated that there is noπ-dimer formation in single crystal for PFP-OR2,and it showed a moderate stability with a half-life times in air-saturated toluene solution of 10 days.Therefore,the dimerization behavior and stability of olympicenyl radicals can be regulated by different substituents.