Hybridized Host Functions in Polyaromatic Tube-in-Capsule Composites

Noncovalent hybridization of two types of host compounds has emerged as a promising strategy to develop unique functions, unattainable by either of the hosts. Here we report unusual spectroscopic features observed within a new hybrid host, formed by the combination of a polyaromatic tube and capsule, with rigid and flexible frameworks, respectively, in water. The resultant tube-in-capsule host selectively encapsulates rod-like aromatic dyes (e.g., BODIPY and coumarin derivatives), yielding ternary host-guest composites bearing a dye-in-tube structure. The ternary composites exhibit strong emission (up to Φ_F = ∼60%) from the bound dyes in water, with up to 45-fold enhancement compared to the corresponding dye-in-capsule composites, due to the spatial isolation of the dyes in the tubular cavities. Detailed host-guest studies using dye derivatives and partial tube structures clearly indicate the importance of the rod-like dye shape and tubular cavity for the present photofunctions. Furthermore, unusual remote chiroptical induction of encapsulated achiral dyes is readily demonstrated within a related hybrid host, where the achiral capsule is replaced with a chiral polyaromatic capsule. The dye-based, pronounced circularly polarized emission (|g_lum| = ∼3 × 10^-3) is observed only in this hybridized host-guest system.