Luminescent nano/micro molecular crystals with well-defined shapes and morphologies have exhibited great potential for various photonic applications. The molecular orientation and packing greatly influence the optical and electronic characters of the crystals. Noncovalent intermolecular interactions can not only determine the growth direction but also induce the formation of polymorphs, bringing more possibilities for the property optimization and functional applications. Besides, light-harvesting energy transfer (LHEnT) is a vital process in natural photosynthesis, the mimic of which provides a simple and practical means for solar energy conversion and the preparation of luminescent materials. With an energy donor and acceptor pair with suitable energy levels and similar molecular size and solubility, it is convenient to fabricate LHEnT molecular crystals with tunable optoelectronic and emission properties by dispersing acceptors into the donor lattices.

We describe in this Account our recent research progress on the use of octahedral iridium (Ir) and ruthenium (Ru) complexes to prepare luminescent crystals for potential applications in nanophotonics. By introducing simple substituents on the coordination ligands, such as a methyl group, fluoro atom, and trifluoromethyl group, as the functional unit to direct assembly, we have been able to obtain well-defined nano/microcrystals from these complexes. Furthermore, by using a molecular doping strategy accompanied by the LHEnT process, the obtained binary crystals show efficient and tunable luminescence properties. With these endeavors, we have realized the luminescence amplification of an Ir energy acceptor that suffers severely from the aggregation-caused quenching effect. Molecular crystals with high-performance linearly polarized luminescence, circularly polarized luminescence, and electrochemiluminescence have been prepared, and their applications in polarized light waveguides and chemical sensing have been demonstrated. By using a stepwise binary assembly method, optical heterostructures are prepared to show their potential in optical information processing and thermosensing.