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Metal ion linked multilayers offer a means of controlling interfacial energy and electron transfer for a range of applications including solar energy conversion, catalysis, sensing, and more. Despite the importance of structure to these interlayer transfer processes, little is known about the distance and orientation between the molecules/surface of these multilayer films. Here we gain structural insights into these assemblies using a combination of UV-Vis polarized visible attenuated total reflectance (p-ATR) and Förster Resonance Energy Transfer (FRET) measurements. The bilayer of interest is composed of a metal oxide surface, phosphonated anthracene molecule, Zn(II) linking ion, and a platinum porphyrin with one (P1), two (P2), or three (P3) phenylene spacers between the chromophoric core and the metal ion binding carboxylate group. As observed by both time-resolved emission and transient absorption, the FRET rate and efficiency decreases with an increasing number of phenylene spacers (P1 > P2 > P3). However, from p-ATR measurements we observe a change in orientation of porphyrins in the bilayer, which inhibits a uniform determination of the orientation factor (κ2) across the series. Instead, we narrow the scope of viable structures by determining the best agreement between experimental and calculated FRET efficiencies. Additionally, we provide evidence that suggests, for the first time, that the bilayer structure is similar on both planar and mesoporous substrates. 

Self-assembly of sensitizer and acceptor molecules has recently emerged as a promising strategy to facilitate and harness photon upconversion via triplet–triplet annihilation (TTA-UC). In addition to the energetic requirements, the structure and relative orientation of these molecules can have a strong influence on TTA-UC rates and efficiency. Here we report the synthesis of five different acceptor molecules composed of an anthracene core functionalized with 9,10- or 2,6-phenyl, methyl, or directly bound phosphonic acid groups and their incorporation into self-assembled bilayers on a ZrO 2 surface. All five films facilitate green-to-blue photon upconversion with Φ uc as high as 0.0023. The efficiency of TTA, and not triplet energy transfer, fluorescence, or losses via FRET, was primarily responsible for dictating the Φ uc emission. Even for molecules having similar photophysical properties, variation in the position of the phosphonic acid resulted in dramatically different Φ TTA , I th values, γ TTA , and D . Interestingly, we observed a strong linear correlation between Φ TTA and the I th value but the cause of this relationship, if any, is unclear.