The first exampleof octasubstituted 2,3-naphthatoc.yanines showingdiscoticmesophase bebaviour is described. @ 1997ElsevierScienceLtd.
Interestin phthalocyanines hasincreasedenormouslyin recentyearsowingto theirintriguingelectrical, optical,photochemicaland catalytic properties.] While there havebeen extensivestudiesof the chemistry, propertiesandapplicationsof thisfascinatingclassof compounds, therehasbeenmuchless workcarriedouton therelated2,3-naphthalocyanine system.z Thebenzofusionon the macrocycliccorerendersthesecompounds absorbing strongly in the near-IR region and exhibiting superior electrical properties compared with phthaiocyanines,q that havealsobeensupportedby theoreticrd calctdations.4Substituted2,3-naphthalocyanines in particularare rare which may be due to the lack of convenientsyntheticroutes to their precursors2,3dicyanonaphthalenes.Considerableprogresshas only been made in this respect very recently.s Here we describetwo syntheticpathwaysto differentlysubstituted2,3-naphthalocy anines 1-3. These macrocycles incorporatedwitheightlong-chainsubstituentsexhibitliquidcrystallineproperties.Althoughphthalocyaninebasedliquidcrystalsare well-documented,6 to our knowledge, the compounds1-3representthe fwstdiscotic mesogensbasedon 2,3-naphthrdocyanine core.
The synthetic routes to octasubstituted zinc naphthalocyanines1-3 are shown in Scheme 1.7,8 Treatmentof l,2,4,5-tetrabromobenzene withbutyllithiumand2,5-dimethylfuran gavethe endoxide4, which underwent deoxygenation yieldingthe dibromonaphthalene 5. Benzylicbrominationfollowedby alkoxylation introducedtwolong-chainsubstituentsto the naphthalenering. Thedibromides7 and8 werethenconvertedto the respectivedinitriles 9 and 10 by using the Rosenmund-vonBraunreaction. The 6,7-disubstituted2,3dicyanonaphthalene 11 was prepared by a different strategy which involved the aromatic nucleophilic substitutionof 12withthiolateNaSC12H25. Thisdinitrilewasdescribedpreviouslyandwasconvertedto the correspondingmetal-freeand coppernaphthalocyanines.9 Cyclisationof dicyanonaphthalenes 9-11withzinc acetateand 1,8-diazabicyclo[5 .4.Olundec-7-ene (DBU)in l-hexanolledto the formationof 1-3,respectively, in moderateyields. All of these macrocyclespossessgood volubilityin commonorganic solventsand were purifiedmainlyby columnchromatography withhexaneortoluenemixedwithtetrahydrofuran (THF)as eluent. Thelatterwasemployedin orderto disruptthe molecularaggregation associatedwiththelargez-system.