Abstract
4,4-Difluoro-3a,4a-diaza-4-bora-s -indacenes, commonly named boron dipyrromethene dyes (F -Bodipy), were utilized as precusors to 4,4-diethynyl-3a,4a-diaza-4-bora-s -indacenes. Symmetrically substituted 4,4-diethynyl-3a,4a-diaza-4-bora-s -indacenes were synthesized using substituted ethynyllithium reagents, while the use of a 1:1 mixture of two different ethynyl Grignard reagents gave dissymmetric products. Using (trialkylsilyl)ethynyllithiums (alkyl = Me, Et) gave 4,4-bis[(trialkylsilyl)ethynyl]-3a,4a-diaza-4-bora-s -indacenes, that in the case of the trimethylsilyl derivative could be deprotected to give the mono- or dideprotected product. The dideprotected 4,4-diethynyl-3a,4a-diaza-4-bora-s -indacene was coupled with bromopyrene, -anthracene, or -terpyridine to give the corresponding 4,4-bis(arylethynyl)-3a,4a-diaza-4-bora-s -indacenes. The monodeprotected 4-ethynyl-4-[(trimethylsilyl)ethynyl]-3a,4a-diaza-4-bora-s -indacenes were either coupled with bromopyrene and then deprotected and oxidatively homocoupled or directly oxidatively homocoupled to give the 1,4-bis(3a,4a-diaza-4-bora-s -indacen-4-yl)butadiyne products. The synthesis of disymmetric 3a,4a-diaza-4-bora-s -indacenes allows the design of fluorescent dyes bearing various functionalities including an oxazoline ring. All the dyes synthesized are strongly fluorescent and redox active and cascade energy transfer is evidenced when excited in the pyrene fragment.
Key words
bodipy - alkynes - boron - luminescence - energy transfer
