Abstract
Molecular photoswitches based on the norbornadiene–quadricylane (NBD–QC) couple have been proposed as key elements of molecular solar thermal energy storage schemes. To characterize the intrinsic properties of such systems, reversible isomerization of a charge-tagged NBD–QC carboxylate couple is investigated in a tandem ion mobility mass spectrometer, using light to induce intramolecular [2 + 2] cycloaddition of NBD carboxylate to form the QC carboxylate and driving the back reaction with molecular collisions. The NBD carboxylate photoisomerization action spectrum recorded by monitoring the QC carboxylate photoisomer extends from 290 to 360 nm with a maximum at 315 nm, and in the longer wavelength region resembles the NBD carboxylate absorption spectrum recorded in solution. Key structural and photochemical properties of the NBD–QC carboxylate system, including the gas-phase absorption spectrum and the energy storage capacity, are determined through computational studies using density functional theory.
Highlights
Molecular photoswitches based on the norbornadiene−quadricylane (NBD−QC) couple have been proposed as key elements of molecular solar thermal energy storage schemes
One proposed solution involves photochemical energy storage via isomerization reactions, whereby photochromic molecules are converted by solar radiation into metastable isomers with release of the stored energy achieved through either thermal, catalytic, electrochemical, or photochemical activation.[1−5] This approach, known as a molecular solar thermal (MOST) system,[6] or solar thermal fuel system,[7] has the potential to integrate the capture and storage of energy in a single molecular system
We report gas-phase photochemical data for a charge-tagged NBD−QC system with photoisomerization of the NBD form to the QC form and back-conversion mediated by energetically controlled collisions with buffer gas
Summary
Molecular photoswitches based on the norbornadiene−quadricylane (NBD−QC) couple have been proposed as key elements of molecular solar thermal energy storage schemes. The ATD peak at 18.0 ms is assigned to the more stable NBD carboxylate isomer, whereas the peak at 18.3 ms, which appeared after the solution in the electrospray syringe was exposed to 315 nm light, is assigned to the less stable QC carboxylate isomer, which lies 25.8 kcal/ mol higher in energy (see the Supporting Information for calculation details).
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