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We present the first high-resolution rotational spectrum of an artificial molecular rotary motor. By combining chirped-pulse Fourier transform microwave spectroscopy and supersonic expansions, we captured the vibronic ground-state conformation of a second-generation motor based on chiral, overcrowded alkenes. The rotational constants were accurately determined by fitting more than 200 rotational transitions in the 2-4 GHz frequency range. Evidence for dissociation products allowed for the unambiguous identification and characterization of the isolated motor components. Experiment and complementary quantum-chemical calculations provide accurate geometrical parameters for the C27H20 molecular motor, the largest molecule investigated by high-resolution microwave spectroscopy to date. [ABSTRACT FROM AUTHOR]

An artificial molecular motor has been studied by chirped‐pulse Fourier transform microwave spectroscopy. In their Communication on page 11209 ff., M. Schnell et al. combine high‐resolution spectroscopy with supersonic jets to capture a snapshot of the functional nanomachine in the gas phase. In the picture, a cold molecular beam of the molecular motors is probed using microwave fields with aligned dipole moments. The spectral film shows highly resolved rotational transitions, which led to an unambiguous structural assignment. [ABSTRACT FROM AUTHOR]