Molecular Orientation and Energy Transfer Dynamics of a Metal Oxide Bound Self-Assembled Trilayer

Self-assemblyof molecular multilayers via metal ion linkages hasbecome an important strategy for interfacial engineering of metalloidand metal oxide (MO x ) substrates, withapplications in numerous areas, including energy harvesting, catalysis,and chemical sensing. An important aspect for the rational designof these multilayers is knowledge of the molecular structure-functionrelationships. For example, in a multilayer composed of differentchromophores in each layer, the molecular orientation of each layer,both relative to the adjacent layers and the substrate, influencesthe efficiency of vectorial energy and electron transfer. Here, wedescribe an approach using UV-vis attenuated total reflection(ATR) spectroscopy to determine the mean dipole tilt angle of chromophoresin each layer in a metal ion-linked trilayer self-assembled on indium-tinoxide. To our knowledge, this is the first report demonstrating themeasurement of the orientation of three different chromophores ina single assembly. The ATR approach allows the adsorption of eachlayer to be monitored in real-time, and any changes in the orientationof an underlying layer arising from the adsorption of an overlyinglayer can be detected. We also performed transient absorption spectroscopyto monitor interlayer energy transfer dynamics in order to relatestructure to function. We found that near unity efficiency, sub-nanosecondenergy transfer between the third and second layer was primarily dictatedby the distance between the chromophores. Thus, in this case, theorientation had minimal impact at such proximity.

Automated summary

Self-assembly of molecular multilayers via metal ion linkages is an important strategy for interfacial engineering applications. In this study, the orientation of chromophores in a metal ion-linked trilayer was determined using UV-vis attenuated total reflection spectroscopy. The ATR approach allowed real-time monitoring of layer adsorption and detection of orientation changes. Transient absorption spectroscopy was also performed to study interlayer energy transfer dynamics.