Photoluminescent Anisotropy Amplification in Polymorphic Organic Nanocrystals by Light-Harvesting Energy Transfer

Polymorphism
and anisotropy are fundamental phenomena of crystalline
materials. However, the structure-dependent photoluminescent (PL)
anisotropy in polymorphic organic crystals has remained unexplored.
Herein, two polymorphic nanocrystals, green-emitting nanorods (PtD-g) and yellow-emitting nanoplates (PtD-y),
were obtained from a platinum­(II)−β-diketonate complex.
The PtD-y crystals display remarkable PL anisotropy with
an anisotropy ratio of up to 0.87 whereas the emission of the PtD-g crystals is nearly unpolarized. The polarization properties
are rationalized on the different molecular packing of these crystals.
By light-harvesting energy transfer, the PtD-y crystals
are successfully used to amplify the emission polarization of a red-emitting
platinum acceptor (PtA) doped into the donor crystalline
matrix, which is otherwise weakly polarized as pure crystals.