Abstract
Molecular photoswitches provide an extremely simple solution for solar energy conversion and storage. To convert stored energy to electricity, however, the photoswitch has to be coupled to a semiconducting electrode. In this work, we report on the assembly of an operational solar-energy-storing organic-oxide hybrid interface, which consists of a tailor-made molecular photoswitch and an atomically-defined semiconducting oxide film. The synthesized norbornadiene derivative 2-cyano-3-(4-carboxyphenyl)norbornadiene (CNBD) was anchored to a well-ordered Co3O4(111) surface by physical vapor deposition in ultrahigh vacuum. Using a photochemical infrared reflection absorption spectroscopy experiment, we demonstrate that the anchored CNBD monolayer remains operational, i.e., can be photo-converted to its energy-rich counterpart 2-cyano-3-(4-carboxyphenyl)quadricyclane (CQC). We show that the activation barrier for energy release remains unaffected by the anchoring reaction and the anchored photoswitch can be charged and discharged with high reversibility. Our atomically-defined solar-energy-storing model interface enables detailed studies of energy conversion processes at organic/oxide hybrid interfaces.
Highlights
Molecular photoswitches provide an extremely simple solution for solar energy conversion and storage
Macroscopic heat release from a molecular solar thermal (MOST) storage device was demonstrated with a reversibility of more than 99.8% per storage cycle[13]
The photoswitchable NBD monolayer was prepared from the NBD derivative 2-cyano-3-(4-carboxyphenyl)norbornadiene (CNBD) shown in Fig. 1a
Summary
Preparation and properties of the model interface. The photoswitchable NBD monolayer was prepared from the NBD derivative 2-cyano-3-(4-carboxyphenyl)norbornadiene (CNBD) shown in Fig. 1a (see the Methods section for synthesis and Supplementary Methods for properties). The surface of the Co3O4(111) film has been characterized in detail by scanning tunneling microscopy (STM) and lowenergy electron diffraction I–V analysis (LEED-IV). It is terminated by a layer of Co2+ ions in the tetrahedral positions of the Co3O4 spinel structure (see Fig. 1a). In order to verify that CNBD can be evaporated without decomposition, we deposited a multilayer film onto Co3O4(111) and compared the infrared reflection absorption spectrum to the spectrum recorded in transmission (see Fig. 1c). The band at 1400 cm−1 is attributed to the symmetric a TR-IRAS
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