Sandeep Cherumukkil, Samrat Ghosh, Vakayil K. Praveen, and Ayyappanpillai Ajayaghosh*
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 -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…F–B bonding in the sheared or xerogel states, which facilitates strong exciton coupling and the resultant NIR emission.
Chem. Sci., 2017, 8, 5644–5649.
Full Text Link: http://dx.doi.org/10.1039/C7SC01696D (Open Access)