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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.
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Differentiating Intra-Assembly and Interlayer Energy Transfer in Metal-Ion-Linked Molecular Multilayers
Metal-ion-linked molecular multilayers on metal oxide surfaces are promising for applications ranging from solar energy conversion to sensing. Most of these applications rely on energy and electron transfer between layers/molecules which can be envisioned to occur via intra-assembly (IA; between metal-ion-linked molecules) and interlayer (IL; between separate layers of nonlinked molecules) processes. Here, we describe our effort to differentiate between IL and IA energy transfer using a bilayer composed of ZrO2, a phosphonated anthracene derivative (A), a zinc(II) linking ion, and a Pt(II)porphyrin (P). Both time-resolved emission and transient absorption measurements show no impact of diluting the anthracene layer with a spectroscopically inert spacer on the rate of 1A* to P and 3P* to A, singlet, and triplet energy transfer, respectively. These results indicate that energy transfer within the metal-ion-linked assembly (i.e., ZrO2-A–Zn-P) is more rapid than with an adjacent, nonlinked A molecule, even for a P derivative capable of laying down on the surface. These insights are an important step toward structural design principles maximizing the efficiency/rate of energy transfer in multilayer assemblies.
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- PAR ID:
- 10572084
- Publisher / Repository:
- American Chemical Society
- Date Published:
- Journal Name:
- The Journal of Physical Chemistry C
- Volume:
- 128
- Issue:
- 40
- ISSN:
- 1932-7447
- Page Range / eLocation ID:
- 16861 to 16868
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1021/acs.jpcc.4c04033
