Anchoring of a Carboxyl-Functionalized Norbornadiene Derivative to an Atomically Defined Cobalt Oxide Surface

Abstract

We have investigated the anchoring of the molecular energy carrier norbornadiene (NBD) to an atomically defined oxide surface. To this end, we synthesized a carboxyl-functionalized NBD derivative, namely 1-(2′-norbornadienyl)­pentanoic acid (NBDA), and deposited it by physical vapor deposition (PVD) under ultrahigh vacuum (UHV) conditions onto a well-ordered Co3O4(111) film grown on Ir(100). In addition, we performed a comparative growth study with benzoic acid (BA) under identical conditions which was used as a reference. The interaction and orientation of NBDA and BA with the oxide surface were monitored in situ during film growth by isothermal time-resolved infrared reflection–absorption spectroscopy (TR-IRAS), both below and above the multilayer desorption temperature. The thermal behavior and stability of the films were investigated by temperature-programmed IRAS (TP-IRAS), with help of density functional (DF) calculations. BA binds to Co3O4(111) under formation of a symmetric chelating carboxylate with the molecular plane oriented nearly perpendicular to the surface. At low temperature (130 K), intact BA physisorbs in form of dimers on top of the saturated monolayer. Upon annealing to 155 K, a reordering transition is observed, in which BA in the multilayer adopts a more flat-lying orientation. The BA multilayer desorbs at 220 K, whereas the surface-anchored BA monolayer is stable up to 400 K. At higher temperature (400–550 K), desorption and decomposition are observed. Very similar to BA, NBDA binds to Co3O4(111) by formation of a symmetric chelating carboxylate. In the multilayer, which desorbs at 240 K, hydrogen-bonded NBDA dimers are formed. Upon PVD of NBDA at 300 K, only a surface anchored carboxylate is stable. The anchored NBDA film shows a characteristic restructuring behavior as a function of coverage. At low coverage the NBDA, adopts a flat-lying structure in which the norbornadiene unit interacts with the Co3O4 surface. With increasing coverage, the norbornadiene units detach from the oxide and the NBDA adopts an upright-standing orientation. Similar to BA, the anchored film is stable up to 400 K and decomposes in the temperature region between 400 and 550 K, leaving behind hydrocarbon residues on the oxide surface.

Solar energy storage at an atomically defined organic-oxide hybrid interface

“…At higher temperature, several weaker bands are observed, which we attribute to decomposition products of CNBD formed at higher temperature. The behavior is consistent with other carboxylate films, studied previously on the same surface 24,31 .…”

“…2a, infrared reflection absorption spectra are displayed, which were recorded during the deposition of a multilayer film at 110 K. At the initial stage of deposition, the IR spectra are dominated by a broad band at 1400 cm −1 , while the ν(C = O) band of the carboxylic acid at 1700 cm −1 is the most intense feature at larger exposure. The band at 1400 cm −1 is attributed to the symmetric stretching mode ν s (OCO) of a surface-bound carboxylate 24,29,30 . It indicates that CNBD anchors to the surface by deprotonation and formation of a chelating surface carboxylate that is attached to the surface Co 2+ ions.…”

“…While anchored NBD films could be prepared recently 24 , a functioning energy-storing hybrid interface, consisting of a photoswitchable NBD monolayer bound to an oxide surface, has not been reported to date. In this work, we demonstrate photochemical switching in an anchored NBD monolayer bound to an atomically defined oxide surface.…”

Storing energy with molecular photoisomers

“…Related model studies were performed using a Co 3 O 4 (111) surface with an atomically defined structure. 118,[120][121][122][123] Monolayer films of NBD derivatives with a carboxylic acid functionality were prepared in which the carboxylic acid group serves as an anchor and binds to the surface Co 2+ ions by forming a chelating surface carboxylate. 120 Using the NBD-derivative 2-cyano-3-(4-carboxyphenyl)norbornadiene (CNBD), the authors prepared a hybrid interface with an anchored QC derivative on Co 3 O 4 (111) in UHV (Figure 6B).…”

“…118,[120][121][122][123] Monolayer films of NBD derivatives with a carboxylic acid functionality were prepared in which the carboxylic acid group serves as an anchor and binds to the surface Co 2+ ions by forming a chelating surface carboxylate. 120 Using the NBD-derivative 2-cyano-3-(4-carboxyphenyl)norbornadiene (CNBD), the authors prepared a hybrid interface with an anchored QC derivative on Co 3 O 4 (111) in UHV (Figure 6B). Photochemical conversion and thermally activated back-conversion were possible even in monolayer films, and photochemical IR spectroscopy experiments in UHV showed high reversibility (98.5%).…”