Rapidly Grown Hexagonal Organic Microtubes Using Ionic Liquids for an Enhanced Optical Waveguide Effect

An optical waveguide that transmits the electromagnetic waves is a critical component for various optoelectrical applications including integrated optical circuits and optical communications. Among many, the 1D tubular optical waveguide structure enables efficient distant energy transfer via mode selection within the optical microcavity. However, its application is limited due to the complicated fabrication process. Herein, hexagonal tris(8-hydroxyquinoline) aluminum (Alq₃) microtubes with an average longitudinal length of ≈15 µm are self-assembled within few minutes by utilizing 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF₄) ionic liquids. The swift fabrication is enabled by the high electron affinity of BMIMBF₄ that forms hexagonal microrods. Also, BMIMBF4 ionic liquid etches the central region of micorods during its growth, forming microtubes with a wall thickness of ≈650 nm. The fabricated Alq₃ microtubes show significantly improved waveguide characteristics with reduced optical loss coefficient (0.054 µm⁻¹) compared to that of microrods (0.271 µm⁻¹). The demonstrated method to fabricate Alq₃ microtubes with ionic liquid is an efficient approach to utilize organic microstructures as an optoelectrical components for advanced optical communications.