Triplet-triplet annihilation upconversion through triplet energy transfer at a nanoporous solid-liquid interface

The triplet-triplet annihilation (TTA) upconversion (UC) through the triplet energy transfer (TET) from the sensitizer fixed on the solid surface to free emitters dissolved in solution was reported. Carboxylic-acid derivative of Pt-porphyrin was used as a sensitizer to fix on the amino-treated surface of continuous nano pore of porous glass without aggregation. UC emission was observed under photoexcitation of 532 nm when the porphyrin-fixed glass was immersed in the emitter solution with 9,10-diphenylanthracene (DPA), showing that TET occurs through the solid-liquid interface. The dynamics of the TET was studied by measuring both phosphorescence decay of sensitizer and rise of the UC emission from emitter. It was found that there were two TET components with different rate constants, which were by one or two orders of magnitude slower than that of diffusion-controlled reaction in solution; nevertheless, the TET rates from solid surface were still fast enough to obtain a high quantum yield of TET for the solid-liquid interface. By melting DPA and soaking it into the sensitizer-fixed porous glass, we fabricated all solid system having bulk interface for TTA-UC.