Energy transfer in ternary macrocycle complexes

Certain commercially available macrocycles, such as gamma-cyclodextrin and [8]-cucurbuturil, are able to form three-component complexes with two small-molecule guests. These ternary complexes have been exploited for catalytic applications. Energy transfer between the two small-molecule guests has rarely been investigated, although efficient energy transfer could be used in a variety of sensing applications. Reported herein is the generation of ternary complexes with gamma cyclodextrin, anthracene, and a series of near-infrared emitting squaraine dyes. These ternary complexes demonstrate efficient fluorescence-based energy transfer. Exciting the anthracene at 350 nm results in efficient energy transfer to and emission from the squaraine molecules at approximately 700 nm. Without the gamma-cyclodextrin, no energy transfer is observed. These results have substantial potential applications, for example, in the detection of explosives via ternary-complex formation and energy transfer.