Triplet-Triplet Annihilation-Based Upconversion in Rod-Like Silica Capsules

Most reported triplet-triplet annihilation upconversion (TTA-UC) platforms rely on isotropic spherical particles, leaving shape-derived functions of anisotropic carriers largely unexplored. Here, we developed rod-like silica capsules (UC RCs) by loading hollow mesoporous silica rods with a PdTPBP/perylene/squalene-based TTA-UC oil and sealing the mesopores with an additional silica layer, which effectively suppressed oil leakage during ethanol exposure and dry-powder storage. In aqueous suspension, UC RCs exhibited red-to-blue TTA-UC under low-intensity excitation, with a threshold intensity of 55 mW cm^{- 2} and an upconversion quantum yield of 1.47%. To add spatial controllability to these efficient upconverting microcarriers, we harnessed their rod-like geometry and investigated their electric-field response. Coupled-dipole calculations and rotational Monte Carlo simulations showed that shape-derived polarizability anisotropy favors field-parallel orientation, with an equilibrium mean angle of approximately 2.3° under the modeled electric field. Consistent with this prediction, UC RCs were aligned in a hydrogel matrix under an AC electric field while retaining their upconversion capability. To the best of our knowledge, this is the first demonstration of field-aligned anisotropic TTA-UC silica capsules embedded in a hydrogel matrix. These anisotropic microcarriers hold great promise for developing patterned luminescent materials, anti-counterfeiting platforms, and advanced photonic architectures.