Organic dyes and organic–inorganic hybrids emit efficiently in the aggregate state. Scientists are in hot pursuit of new materials that can luminesce efficiently in the solid state because luminophores must exist as solids in almost all applications. Two research groups at the Chinese Academy of Sciences in Beijing have developed materials whose nanoaggregates emit more efficiently than their solutions, behaving exactly oppositely to most common fluorophores.
The first group, led by Y. Li and G. Yang, discovered a class of organic dyes that emit intense green light in the aggregate state, whereas their solutions are practically nonluminescent. For example, the emission efficiency of the nanorod aggregates of one of the dyes (1) is 112-fold higher than that of its solution. The authors suggest that restricted intramolecular motion and ready intramolecular proton transfer of the dye molecules in the aggregates cause the aggregation-induced emission. (J. Phys. Chem. B2007,111,5861–5868)
The second group, led by another Y. Li, found that light emission from dye 2 was greatly enhanced when the molecule was hybridized with gold nanoparticles. This phenomenon was, however, not observed in the congener with only one dithiolanyl group. The researchers concluded that the hybridization-enhanced emission is due to the restriction of intramolecular rotation of the dye molecules imposed by the formation of Au–2–Au structures, in which each molecule of dye 2 was bound to the surfaces of two gold nanoparticles via the strong S–Au interaction. (Langmuir2007,23,6754–6760; Ben Zhong Tang) Go to top