Double J-Coupling Strategy for Near Infrared Emitters.

Fluorophores emitting in the near-infrared (NIR) are highly desired for various applications, but increasing nonradiative rates cause severe fluorescence quenching for wavelengths beyond 800 nm. Here, a bis(squaraine) dye is reported that bears two NIR dyes in a head-to-tail chromophore arrangement. This arrangement leads to molecular J-type exciton coupling, resulting in an absorption maximum at 961 nm and a fluorescence peak at 971 nm with a quantum yield of 0.33% in chloroform. In less polar toluene, the bis(squaraine) self-assembles into nanofibers, affording another bathochromic shift with an absorption maximum at 1095 nm and a fluorescence peak at 1116 nm originating from molecular J-type coupling.