Homogeneous and Heterogeneous Self-Assembly of Luminescent Pyromellitic Dianhydride-Based Charge-Transfer Complexes

Using easily hydrolyzable brominated pyromellitic dianhydride (PMDA) as an electron acceptor, a wide variety of structurally stable binary organic charge-transfer (CT) microcrystals that are stabilized by dominant intermolecular CT interactions is achieved. By varying the electron-donating abilities of pi-electron compounds, the resulting single crystalline CT assemblies display tailorable fluorescence emissions spanning from green to near-infrared. Upon implantation of a pi-electron donor anthracene (An) into fluoranthene-PMDA (Fl-PMDA), red and NIR emissions of ternary alloyed assemblies are substantially enhanced due to efficient energy transfer from Fl-PMDA to An-PMDA as well as structural complementarity between two CT complexes. Depending on the well-matched epitaxial relationship, seeded growth of phenanthrene-PMDA (Ph-PMDA) onto the pre-existing An-PMDA microcrystals is also achieved, leading to core-shell heterostructures with full and partial coverage. Such an epitaxial growth strategy is also applicable to the construction of microscale heterostructures of diverse CT complex combinations. The ternary Fl(1-x)An(x)-PMDA alloyed assemblies display composition-dependent tailorable optical waveguiding behaviors. While An-PMDA@Ph-PMDA core-shell microrods present wavelength-dependent two-photon excited fluorescence performances. The rational creation of these homogeneous and heterogeneous CT-assembled architectures provides us a deep insight to investigate multicomponent functional organic cocrystals.