Glass-forming binaphthyl chromophores

The use of the binaphthyl framework to synthesize glass-forming organic chr omophores is described. Suzuki coupling reactions of racemic 6,6 ' -dibromo -2,2 ' -dialkoxy-1,1 ' -binaphthyl with 1,1-diphenyl-2-(4-dihydroxyboron-ph enyl-)-ethene using [Pd(dppf)Cl-2] (dppf = 1,1 ' -bis(diphenylphosphino)fer rocene-) as the catalyst provide a set of chromophores with the 4-(2,2 ' -d iphenyl-vinyl)-1-phenyl group at the 6- and 6 ' -positions and a range of g roups 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 ' -bi naphthyl compounds with styrene provide chromophores of the ty pe 2,2 ' -di alkoxy-1,1 ' -binaphthyl-6,6 ' -bis(2-phenyl-vinyl). Starting with enantiom erically enriched (R)-2Hex, one obtains (R)-4Hex. Molecules of the type 4 c ontain two 1-naphthyl-2-phenyl ethylene chromophores with a pseudo-orthogon al relationship. Similar procedures can be used to obtain fragments with mo re extended conjugation length. Thus, the Heck coupling reaction of 2Hex wi th 4-(4 ' -tert-butylstyryl)styrene, 1-(4 ' -tert-butylstyryl)-4-(4 ' -viny lstyryl)benzene, and 1-(3 ' ,5 ' -dihexyloxystyryl)4-(4 ' -vinylstyryl)benz ene provides 5Hex, 6Hex, and 7Hex, respectively. DSC measurements and powde r diffraction experiments indicate that the bi-naphthol chromophores show a resistance to crystallization. In some cases, considerably different therm al behavior is observed between enantiomerically enriched samples and their racemic counterparts. Increasing the size of the conjugated fragment on th e binaphthol core leads to materials with higher glass-transition temperatu res and a less pronounced tendency to crystallize. Fluorescence spectroscop y gives evidence of "excimer"-type interactions in the solid state, except for the chromophores with 4-(2,2 ' -diphenylvinyl)-1-phenyl groups. It is p ossible to obtain amorphous films of these chromophores directly from solut ion, and to fabricate light-emitting diodes, in which the electroluminescen t layer corresponds to the binaphthyl chromophore.