An unprecedented amplification of near-infrared emission in a Bodipy derived π-system by stress or gelation

We report an unprecedented strategy to generate and amplify near-infrared (NIR) emission in an organic chromophore by mechanical stress or gelation pathways. A greenish-yellow emitting film of pi-extended Bodipy-1, obtained from n-decane, became orange-red upon mechanical shearing, with a 15-fold enhancement in NIR emission at 738 nm. Alternatively, a DMSO gel of Bodipy-1 exhibited a 7-fold enhancement in NIR emission at 748 nm with a change in emission color from yellow to orange-red upon drying. The reason for the amplified NIR emission in both cases is established from the difference in chromophore packing, by single crystal analysis of a model compound (Bodipy-2), which also exhibited a near identical emission spectrum with red to NIR emission (742 nm). Comparison of the emission features and WAXS and FT-IR data of the sheared n-decane film and the DMSO xerogel with the single crystal data supports a head-to-tail slipped arrangement driven by the N-H center dot center dot center dot F-B bonding in the sheared or xerogel states, which facilitates strong exciton coupling and the resultant NIR emission.