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1Repair Windows errors before they cause bigger problems2Scan for outdated or missing drivers - takes under a minute3Clear out junk files and repair common Windows errorsNorbornadiene can absorb light and rearrange into a strained, higher-energy molecule called quadricyclane, storing energy that can later be released as heat. But “for decades” overstates what the available evidence shows: a 2018 study measured storage lifetimes up to 48.5 days in specific oligomeric molecules, while a 2024 review reports adaptable storage times up to 18 years for selected derivatives. Neither establishes multi-decade storage.
How the light-driven reaction stores energy
The norbornadiene/quadricyclane pair is studied as a molecular solar thermal energy storage system, or MOST; some literature calls these materials solar thermal fuels. When norbornadiene (NBD) absorbs light, a photoinduced [2+2] cycloaddition converts it into quadricyclane (QC). QC has a strained structure and sits at higher energy than NBD. Driving the reverse reaction, called cycloreversion, returns QC to NBD and releases energy as heat. Heat, catalysts and electrochemical methods have all been studied as possible triggers, but no one release method is established as universally best. The 2024 review of the NBD/QC pair surveys these approaches.
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This is chemical heat storage, not an established electricity-storage technology. Research into electrochemical release or electricity generation does not make NBD/QC a commercial battery. A 2020 review describes the field’s engineering challenges and research directions.
What storage times have actually been reported?
The duration depends on the molecule and on what the reported figure represents. In a 2018 study, Mansø and colleagues measured lifetimes up to 48.5 days for NBD/QC photoswitch couples incorporated into dimeric and trimeric structures. A 2024 review summarizes selected substituted NBD/QC systems with adaptable storage times ranging from one hour to 18 years. That upper end is a review-level report for selected derivatives; it is not evidence of a demonstrated multi-decade storage system or a full-scale installation.
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A molecule’s metastable-state lifetime describes how long it can retain its stored chemical energy under the relevant conditions. It does not by itself show how much sunlight a device captures, how much heat it can deliver usefully, or whether it can operate repeatedly at practical scale. The 2018 oligomer study and the 2024 review report different types of evidence, so their figures should not be treated as interchangeable demonstrations.
What the best-known performance figures mean
The headline figures below come from particular compounds and studies, not from NBD/QC systems as a whole.
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| Study and system | Reported result | How to interpret it |
|---|---|---|
| Mansø et al., 2018: dimeric and trimeric NBD/QC photoswitches | Up to 559 kJ/kg (155 Wh/kg) measured energy density; up to 48.5 days measured storage lifetime; up to 94% photoconversion quantum yield per NBD subunit | Measured maxima for the studied oligomer systems. The quantum yield is a per-subunit result, not a guaranteed system-level solar-to-heat efficiency. Nature Communications |
| Mansø et al., 2018: calculated result for the oligomer study | Up to 927 kJ/kg (257 Wh/kg) | A calculated maximum, not the study’s measured maximum. Nature Communications |
| Such et al., 2016: studied low-molecular-weight substituted NBD/QC derivatives | Energy-storage densities of 396–629 kJ/kg | Results for the compounds in that study; they are not a universal range for the molecule pair. Angewandte Chemie International Edition |
| Hemauer et al., 2024: selected substituted NBD derivatives summarized in a review | Adaptable storage-time range of one hour to 18 years | A review-level range for selected systems, not evidence of multi-decade storage. ChemPhysChem |
| Petersen et al., 2019: polymer-film photoswitch system | Up to 10 months lifetime reported in the abstract | A result for the studied film concept, not proof of a commercially available coating. Advanced Science |
The 2018 authors describe the approach as storing solar thermal energy by photoisomerizing molecules into high-energy, metastable isomers. Their reported maxima apply to the specific dimeric and trimeric systems they studied, rather than promising the same performance from every NBD/QC design.
How molecular designs trade one performance goal for another
There is no single figure that determines whether a candidate is useful. A molecule may be strong on one measure and weak on another:
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- Energy density: how much chemical energy is stored for a given mass of material.
- Solar-spectrum absorption: how effectively the molecule absorbs wavelengths present in sunlight.
- Photoconversion quantum yield: how efficiently absorbed light drives the conversion from NBD to QC.
- Metastable-state lifetime: how long the QC form retains its stored energy.
- Release and reversibility: what trigger or catalyst is needed to release heat, and whether the cycle can be repeated reliably.
- System-level efficiency: how much useful heat the complete device delivers after absorption, conversion, storage and release losses.
Structure changes create trade-offs. Adding donor or acceptor groups can shift absorption toward longer wavelengths and improve overlap with sunlight, but the added molecular mass can lower gravimetric energy density. Substitution can also change reaction kinetics and shorten storage time. Likewise, the 2018 oligomer work found that dimeric and trimeric structures could combine high energy density with longer measured lifetimes, but those results depend on the particular molecular structures tested. The relevant comparison is therefore among complete candidate designs, not a claim that one modification improves every metric.
From molecules to films and flow systems
Polymer-embedded films
Researchers have investigated embedding NBD/QC photoswitches in polymer matrices as a route to energy-storing films or coatings. The 2019 study reported a lifetime up to 10 months for its studied polymer-film system. This is a research concept, not evidence that a consumer-ready coating is available. Petersen et al., Advanced Science (2019)
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Continuous-flow processing
A 2026 paper examines kinetics, modeling and continuous-flow implementation for the NBD/QC system. Flow research addresses how the chemistry might be handled in a process, but the existence of a laboratory implementation does not establish commercial readiness. Kambuyi et al., Chemical Engineering Journal (available online 2026)
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A long molecular lifetime is only one component of a working solar-heat storage system. Practical development also has to address:
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- efficient capture of a useful portion of the solar spectrum;
- high conversion yield from NBD to QC under workable illumination;
- stable performance over repeated storage and release cycles;
- effective, controllable heat release with suitable catalysts or other triggers;
- system-level efficiency, including heat losses and the energy required to operate the device; and
- a practical way to contain, circulate or integrate the material.
The 2024 review describes laboratory-scale demonstrations and identifies photoconversion yield, stability and overall efficiency as continuing challenges. Taken together with ongoing flow-process and film research, the evidence supports an active field of energy-storage chemistry—not a ready-made alternative to a home battery or a proven decades-long solar-heat reservoir.
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