Molecular rotors turn copper nanoclusters into efficient light-to-heat materials

Turning light into heat is useful for photothermal therapy, solar-driven heating, laser ignition,
and other materials applications. But at the nanoscale, making this process efficient and
predictable is not straightforward.

In this newly published, open-access Nature Communications study, the authors take a
surprisingly simple route: give copper nanoclusters tiny molecular rotors.
The team designed copper nanoclusters with carboxylate ligands carrying adamantane
groups. In the resulting [Cu₃₆(4-F-PhS)₂₄(AdmCOO)₆(PPh₃)₄H₈]²⁻ nanocluster, the carboxylate
acts as a rigid stator, while the adamantane unit behaves like a freely rotating molecular
rotor. This rotor-stator architecture gives the adamantane enough space to move with very
little resistance.

ADF calculations were key to connecting this molecular motion to the material’s
photothermal performance. The simulations showed that the adamantane rotors have low
rotational barriers not only in the ground state, but also in excited states. Together with NMR
and transient absorption spectroscopy, this revealed a clear mechanism: after light
absorption, energy relaxes through the copper core and is then dissipated through rotor
motion as heat.

The result is a copper nanocluster with a photothermal conversion efficiency of about 75%.
Under 445 nm laser irradiation, the material rapidly heated to 200 °C at 1.0 W cm⁻², while
remaining stable over repeated heating and cooling cycles.
The same design idea also worked beyond one cluster. By changing the rotor type, the
authors prepared a broader family of copper nanoclusters with strong photothermal
performance, including systems active in the near-infrared region.