An Alloy Engineering Strategy toward Helical Microstructures of Achiral π-Conjugated Molecules for Circularly Polarized Luminescence

Helical assembly has been demonstrated to efficiently facilitate the circularly polarized luminescence (CPL) performances, but the synthesis of micro- and nanohelices from rigid achiral π-conjugated compounds remains challenging due to the absence of bilayer structures or complementary hydrogen-bonding interactions. Here, we develop an alloying strategy for the realization of helical microstructures from achiral anthracene/anthracene derivatives with x-/x-axis modification or anthracene/tetracene derivatives with x-/y-axis modification via solution coassembly. Interestingly, two anthracene derivatives bearing asymmetric phenyl/phenylethynyl groups and symmetric phenylethynyl groups can assemble into spiral microribbons with a fractal branching pattern. Using such an alloying strategy, color-tailorable ternary spiral microtubules/microribbons referring to high-efficiency energy transfer processes are achievable. Molecular dynamics simulations reveal that the Von Mises stress produced by symmetry differences of two components induces symmetry breaking of alloy structures associated with twisting. Additionally, the contents of the guest and H₂O also play a vital role in the formation of intricate helical microstructures. Single binary and ternary spiral microribbons present considerable CPL properties with a dissymmetric factor ('g_lum') of more than 0.01. The present work provides new insights into the formation of helical microcrystals with complex topologies and new optoelectronic functions.