ABSTRACT
The use of the binaphthyl framework to synthesize glass-forming organic chromophores is described. Suzuki coupling reactions of racemic 6,6'-dibromo-2,2'-dialkoxy-1,1'-binaphthyl with 1,1-diphenyl-2-(4-dihydroxyboronphenyl)-ethene using [Pd(dppf)Cl2] (dppf = 1,1'-bis(diphenylphosphino)ferrocene) as the catalyst provide a set of chromophores with the 4-(2,2'-diphenylvinyl)-1-phenyl group at the 6- and 6'-positions and a range of groups on the oxygen atom. Starting with enantiomerically enriched (R)-6,6'-dibromo-2,2'-dihexyloxy-1,1'-binaphthyl ((R)-2Hex), one can obtain (R)-3Hex. Heck coupling reactions of 6,6'-dibromo-2,2'-dialkoxy-1,1'-binaphthyl compounds with styrene provide chromophores of the type 2,2'-dialkoxy-1,1'-binaphthyl-6,6'-bis(2-phenyl-vinyl). Starting with enantiomerically enriched (R)-2Hex, one obtains (R)-4Hex. Molecules of the type 4 contain two 1-naphthyl-2-phenyl ethylene chromophores with a pseudoorthogonal relationship. Similar procedures can be used to obtain fragments with more extended conjugation length. Thus, the Heck coupling reaction of 2Hex with 4-(4'-tert-butylstyryl)styrene, 1-(4'-tert-butylstyryl)-4-(4'-vinylstyryl)benzene, and 1-(3',5'-dihexyloxystyryl)4-(4'-vinylstyryl)benzene provides 5Hex, 6Hex, and 7Hex, respectively. DSC measurements and powder diffraction experiments indicate that the binaphthol chromophores show a resistance to crystallization. In some cases, considerably different thermal behavior is observed between enantiomerically enriched samples and their racemic counterparts. Increasing the size of the conjugated fragment on the binaphthol core leads to materials with higher glass-transition temperatures and a less pronounced tendency to crystallize. Fluorescence spectroscopy gives evidence of "excimer"-type interactions in the solid state, except for the chromophores with 4-(2,2'-diphenylvinyl)-1-phenyl groups. It is possible to obtain amorphous films of these chromophores directly from solution, and to fabricate light-emitting diodes, in which the electroluminescent layer corresponds to the binaphthyl chromophore.
