Excited-State Dynamics of Molecular Solar Thermal Fuels

Project Information

DynaMOST

Grant agreement ID: 101103764

DOI

10.3030/101103764

Project closed

EC signature date 12 April 2023

Start date 1 October 2023

End date 30 September 2025

Funded under

• Marie Skłodowska-Curie Actions (MSCA)

Total cost

No data

EU contribution

€ 199 440,96

Coordinated by

UNIVERSITAT WIEN
Austria

Periodic Reporting for period 1 - DynaMOST (Excited-State Dynamics of Molecular Solar Thermal Fuels)

Reporting period: 2023-10-01 to 2025-09-30

Summary of the context and overall objectives of the project

Europe’s transition to a climate-neutral and secure energy system requires technologies that can store solar energy when the sun is available and release it when needed. Molecular Solar-Thermal (MOST) systems address this need by converting sunlight into a higher-energy molecular form and later releasing it as heat on demand. They act as rechargeable heat batteries at the molecular scale. However, only a small number of MOST candidates are currently known, and the factors that determine how much energy they can store, how fast they work, and how efficiently they use light are still poorly understood. This is true both for organometallic MOST fuels based on metal complexes and for purely organic systems such as cyclophanes.

Excited-State Dynamics of Molecular Solar-Thermal Fuels (DynaMOST) is designed to gain a fundamental, quantum-level understanding of how these molecules absorb light and transform into energy-rich forms, and to use this understanding to guide the rational design of new, more efficient, and more sustainable MOST systems. In the longer term, the knowledge produced by the project is expected to support compact solar heat-battery concepts and help reduce reliance on scarce critical raw materials, thereby contributing to the EU’s climate, energy, and resource-security goals.

The central objective of DynaMOST is to find the electronic and nuclear factors favouring the formation of the desired photoproducts in the aforementioned MOST systems and exploit these to design new synthetic targets. The specific Research and Innovation (R&I) objectives (R&IOs) are:

- To explore the quantum mechanical description of ground- and excited-state electronic structures for the organometallic and organic MOST systems (a preparatory workpackage, WP-1): identify the electronic states involved in the photoisomerization reaction.

- To implement theoretical methods beyond the current state-of-the-art for carrying out the dynamical simulations (an interface and implementation workpackage, WP-2): testing and benchmarking.

- To understand the reasons for competing decay pathways after electronic excitation by executing the excited-state molecular dynamics simulations (a dynamical simulation workpackage, WP-3): identification of nuclear and electronic prerequisites to tailor photoproduct formation in solution.

- To suggest novel MOST systems using earth-abundant metals (organometallic) or optimum linker lengths (organic), with higher energy storage and higher quantum yields (a rational design workpackage, WP-4).

- To effectively execute all components of the proposal using the project management, dissemination and communication workpackage, WP-5.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

DynaMOST studied how molecules capture, store and release solar energy in Molecular Solar-Thermal (MOST) systems, and how this knowledge can be used to design better materials. The work progressed along three interconnected fronts, moving from individual molecules to extended materials and linking them through the unifying concept of spin-state control.

Explaining a fundamental difference:
Using high-level electronic-structure calculations and excited-state dynamics, the project clarified why iron-based complexes in the same metal family perform poorly in MOST photoisomerization compared with ruthenium and osmium analogues. During the energy-storage reaction, the iron complex becomes trapped in an unfavourable quantum configuration – a “spin trap” – that blocks efficient energy conversion. In contrast, ruthenium and osmium smoothly access a productive spin pathway, enabling effective solar-energy storage. This result resolves a long-standing puzzle in molecular solar-thermal chemistry and establishes spin-state accessibility as a predictive criterion for MOST performance.

Designing the next generation:
Building on these insights, DynaMOST designed a new class of heterobimetallic complexes that combine a small fraction of an efficient heavy metal (such as osmium) with a lighter, earth-abundant partner (such as molybdenum or tungsten). Quantum-chemical calculations predict that these hybrids avoid the spin trap while maintaining high energy-storage density, matching the performance of state-of-the-art ruthenium systems at much lower cost. This provides a concrete molecular blueprint for efficient, lower-cost MOST materials.

Extending the principle to materials:
In a collaborative effort, a PhD student supervised by the MSCA fellow extended the spin-state concept to a porous, catalyst-like solid, a metal-organic framework (MOF). The study shows that its triangular iron(III)-oxo clusters exhibit spin frustration – a situation where electron spins cannot adopt a single configuration – which governs the material’s stability and reactivity. Published in a leading journal, this work bridges molecular-scale spin physics with the macroscopic properties of functional porous materials and demonstrates that spin-state control is a powerful idea beyond molecular fuels alone.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

DynaMOST delivers several advances beyond the state of the art in molecular solar-thermal and spin-functional materials.

Predictive spin-based design of MOST systems:
By identifying the “spin trap” mechanism that prevents efficient energy storage in certain iron-based systems and showing how access to the correct spin state controls performance, the project turns MOST development from largely empirical screening into rational, rule-based design. Spin-state control emerges as a powerful design principle for deciding which molecular structures are likely to work as efficient solar-thermal fuels.

From molecules to materials:
The discovery of spin frustration in catalytic metal-organic frameworks establishes a new conceptual link between molecular spin chemistry and solid-state functionality. It shows how the way electron spins interact inside triangular iron–oxo clusters governs the stability and reactivity of the material. This provides a new handle to understand and control the behaviour of porous materials that are relevant not only for energy storage but also for gas separation and catalysis.

Blueprint for sustainable energy materials:
The rational design of osmium–molybdenum and osmium–tungsten hybrids provides a concrete route to high-performance MOST systems with drastically reduced cost and environmental footprint compared with purely noble-metal systems. These heterobimetallic candidates avoid the spin trap while maintaining high energy-storage density, and the underlying principles are transferable to other solar-energy and photocatalytic materials based on earth-abundant elements.