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
