Synthesis and optical properties of derivatives of oligobipyridines

Two oligobipyridyl derivatives, 1,4-bis[5′-methyl-(2,2′-bipyridin-5-yl)-ethyl]-benzene (L1) and 5,5′-bis[4′-methyl-(2, 2′-bipyridin-4-yl)-ethyl]-2,2′-bipyridine (L2), which belong to partially conjugated oligomers in structure, were synthesized and found to show strong photoluminescence. In its as-obtained powder states, L1 shows an emission at 403 nm under the excitation of 365 nm; while when mixed with KBr, it shows one emission peak at 402 nm and one shoulder at 389 nm; and in its chloroform solution, it emits with two peaks at 344 nm and 356 nm. The as-obtained powder state of L2 emits with a peak at 418 nm under the excitation of 367 nm, while its doped state in KBr plate has two emissions at 403 nm and 423 nm; in its chloroform solution, two peaks at 393 nm and 414 nm appear under the excitation of 364 nm light. Films of L2 fabricated by vacuum evaporation emit at 406 nm and 428 nm. Both compounds show emission in the range of deep blue or violet color. It is proposed that one way to obtain blue emitting materials is to shorten the conjugation length in the polymeric and oligomeric structures. Silver complex of L1 show emission at 445 nm under the excitation of 348 nm. EL properties of L2 were studied preliminarily.