Supramolecular oligourethane gels as light-harvesting antennae: achieving multicolour luminescence and white-light emission through FRET

Soft luminescent gel materials have many practical applications due to their excellent solution processability, thixotropic, soft and facile coating performance. Here we have prepared a series of oligourethane (OU)-based gelators with fine-tuned optical properties. Chromophores with different π-conjugated lengths were introduced into the backbone in order to systematically control the energy gaps of the OUs. Blue/green/red (BGR) fluorescent gelators were thus achieved. The gelation behavior was driven by non-covalent bonds, notably hydrogen-bonds and van der Waals interactions. Because of the dynamic character of these non-covalent interactions, a simple mixture of sols could revert back to homogeneous hybrid gels. Upon gelation, the extended network of the gels leads to sequential multichromophoric Forster resonance energy transfer (FRET). Benefiting from the presence of three primary colours, the resultant hybrid gel exhibited almost any desired visible emission colour at different ratios of gelators. Of particular significance, a white-light-emitting diode (WLED) was prepared with CIEx,y coordinates (0.35, 0.33) in the hybrid gel formed by precise control over the OUB/OUG/OUR stoichiometry. This type of supramolecular gel holds promise in designing large-area, flexible optical illumination, fluorescent labels and light-harvesting systems, and could be a suitable scaffold for new-generation soft materials with tunable optical properties in display technologies.