Energy Storage in Strained Organic Molecules: (Spectro)Electrochemical Characterization of Norbornadiene and Quadricyclane

Abstract

We have investigated the electrochemically triggered cycloreversion of quadricyclane (QC) to norbornadiene (NBD), a system that holds the potential to combine both energy storage and conversion in a single molecule. Unambiguous voltammetric traces are obtained for pure NBD and pure QC, the latter a strained polycyclic isomer of the former. The difference in redox potentials is smaller than the energy difference between the neutral molecules. This is owing to a significant energy difference between the corresponding radical cations, as demonstrated by density functional theory (DFT) calculations. The vibrational modes of each pure compound are characterized experimentally in the fingerprint region and identified by DFT methods. Thermal and electrochemical transformations of NBD and QC are monitored in situ by IR spectroelectrochemical methods. The kinetics of the cycloreversion of QC to NBD, which is catalyzed by oxidizing equivalents, can be controlled by an applied electrode potential, which implies the ability to adjust in real time the release of thermal power stored in QC.

Solar Energy Storage by Molecular Norbornadiene–Quadricyclane Photoswitches: Polymer Film Devices

“…One solution is to address both light harnessing and storage in a combined technology. Moreover, this process has been shown to occur through a stimulus such as a heterogeneous catalyst, [5] electric potential, [6] or light. [4] Here, energy can be stored in a molecular photoswitch through irradiation under sunlight, resulting in the formation of a high energy isomer.…”

“…Based on our previous studies, [11h,i] we chose to investigate the properties of better aromatic donors used in conjunction with the strong trifluoroacetyl acceptor N4b-d and the double NBD analogs NN4e. 2019, 6,1900367 yields (Scheme 1), primarily due to the strong trifluoroacetyl acceptor activating the alkyne toward the [4+2π] cycloaddition. The acetylenic precursors 3b-e were made following a literature procedure from their corresponding terminal alkynes.…”

“…2019, 6,1900367 Scheme 1. a) Previously studied NBDs (N5a-d, NN5e, and N4a) and compounds made for this study (N4b-d and NN4e). Sci.…”

“…2019, 6,1900367 into PMMA resulted in composites with good cyclability. Ideally, laminated films for temperature regulation require the NBD to have a half-life in the order of 4-8 h. To investigate this, N4b was selected as it has a good solar spectrum overlap (λ onset = 457 nm) and a good quantum yield (Φ = 68%), but most importantly a half-life of just under 7 h in toluene.…”

“…However, daily and seasonal variations in both energy production and consumption compel the development of new energy storage technologies. Moreover, this process has been shown to occur through a stimulus such as a heterogeneous catalyst, [5] electric potential, [6] or light. This has been shown in molecular solar thermal (MOST) storage [3] also referred to as solar thermal fuel (STF).…”