RESUMO
The triplet annihilator is a critical component for triplet-triplet annihilation upconversion (TTA-UC); both the photophysical properties of the annihilator and the intermolecular orientation have pivotal effects on the overall efficiency of TTA-UC. Herein, we synthesized two supramolecular annihilators A-1 and A-2 by grafting 9,10-diphenylanthracene (DPA) fragments, which have been widely used as triplet annihilators for TTA-UC, on a macrocyclic host-pillar[5]arenes. In A-1, the orientation of the two DPA units was random, while, in A-2, the two DPA units were pushed to a parallel arrangement by intramolecular hydrogen-bonding interactions. The two compounds showed very similar photophysical properties and host-guest binding affinities toward electron-deficient guests, but showed totally different TTA-UC emissions. The UC quantum yield of A-2 could be optimized to 13.7% when an alkyl ammonia chain-attaching sensitizer S-2 was used, while, for A-1, only 5.1% was achieved. Destroying the hydrogen-bonding interactions by adding MeOH to A-2 significantly decreased the UC emissions, demonstrating that the parallel orientations of the two DPA units contributed greatly to the TTA-UC emissions. These results should be beneficial for annihilator designs and provide a new promising strategy for enhancing TTA-UC emissions.
RESUMO
The low quantum efficiency in the solid phase and the highly efficient quenching by oxygen are two major weaknesses limiting the practical applications of triplet-triplet annihilation (TTA) upconversion (UC). Herein, we report an organic-inorganic hybrid nanocomposites fabricated by self-assembly of LAPONITE® clay and poly(N-vinyl-2-pyrrolidone) (PVP), which serves as excellent matrix for solid-state TTA-UC even in air. In the hybrid hydrogel doped by TTA-UC components, the anionic acceptors are arranged in an ordered manner at the nano-disk edge through electrostatic attraction, which avoids haphazard accumulation of the acceptors and allows for highly efficient inter-acceptor triplet energy migration. Moreover, the entangled PVP could not only protect the triplet excitons from oxygen quenching but even proactively eliminate oxygen by photoirradiation. Significantly, the dried gel prepared by completely removing water from the hydrogel gave absolute UC quantum efficiencies of up to 23.8% (out of a 50% maximum), which is the highest TTA-UC efficiency obtained in the solid state. The dried gels are readily made into powder by grinding with maintained UC emissions, making them convenient for application to information encryption and anti-counterfeiting security by virtue of the high UC quantum efficiency and insensitivity to oxygen.
