Influence of meta- and para-phosphonated diphenylanthracene on photon upconversion in self-assembled bilayers

It is well known that the rate and efficiency of photon upconversion via triplet–triplet annihilation (TTA-UC) are strongly dependent on the energetics of the sensitizer and acceptor molecules. In rigid scaffoldings, where the dyes are fixed in position, the structure and orientation of the molecules also presumably play an important role. We investigate how the variation in the position of the phosphonate surface binding group on 9,10-diphenylanthracene influences TTA-UC in self-assembled bilayers on ZrO2. Interestingly, meta- or para-substitution of the anthracene dye with phosphonate groups had minimal influence on their energetics, surface loadings, or sensitizer to acceptor triplet energy transfer efficiency. However, the TTA-UC efficiency is three times lower with the meta-substituted dye, which is attributed to its threefold decrease in its triplet excited state lifetime relative to the para-substituted dye.