Sérgio Rosa Domingos

Molecular jet expansions are critical for producing cold molecular beams for gas-phase molecular spectroscopy. Notably, most of the operating instruments in this class of experiments rely on pulsed valves with intrinsic temperature limits that significantly constrain the efficient vaporization of less volatile compounds. Here, we present and benchmark the Thermally Insulating Nozzle (TINo), a new pulsed nozzle design that supports substantially higher vaporization temperatures without compromising valve integrity. As a proof of concept, we integrated TINo into a chirped-pulse Fourier transform microwave spectrometer and recorded the rotational spectrum of 1,8-naphthalimide, a molecule of interest with a melting point of 300 °C. The enhanced signal-to-noise ratio enabled the detection of both the parent species and the singly substituted 13C isotopologues in natural abundance. TINo opens a viable path toward acquiring laboratory spectra of otherwise inaccessible molecular libraries via jet-cooled molecular spectroscopy.

With the goal of manipulating (bio)chemical processes, photoswitches emerge as important assets in molecular nanotechnology. To guide synthetic strategies toward increasingly more efficient systems, conformational dynamics studies performed with atomic rigor are in demand, particularly if this information can be extracted with control over the size of a perturbing solvation layer. Here, we use jet‐cooled rotational spectroscopy and quantum chemistry calculations to unravel the structure and micro‐hydration dynamics of a prototype photoswitch. Camphorquinone‐oxime has a switching function enabled by the oxime moiety, and a chiral subspace generated by camphor, ensuring motion directionality. Although it may seem a relatively simple molecule, several popular levels of theory disagree on the energy ordering of the two switch states. We find that the oxime moiety integrates cooperatively into linear water chains captured for the dimer and trimer topologies, as well as into more exotic three‐dimensional structures created for the complex with the water tetramer. Evidence for concerted hydration dynamics emerges from a comparison between theory and experimental isotopic information. We evaluate the balance of intermolecular forces at play during the hydration network build up and discuss how a flexible first solvation layer may affect the switching dynamics of this class of systems.

With the goal of manipulating (bio)chemical processes, photoswitches emerge as important assets in molecular nanotechnology. To guide synthetic strategies toward increasingly more efficient systems, conformational dynamics studies performed with atomic rigor are in demand, particularly if this information can be extracted with control over the size of a perturbing solvation layer. Here, we use jet‐cooled rotational spectroscopy and quantum chemistry calculations to unravel the structure and micro‐hydration dynamics of a prototype photoswitch. Camphorquinone‐oxime has a switching function enabled by the oxime moiety, and a chiral subspace generated by camphor, ensuring motion directionality. Although it may seem a relatively simple molecule, several popular levels of theory disagree on the energy ordering of the two switch states. We find that the oxime moiety integrates cooperatively into linear water chains captured for the dimer and trimer topologies, as well as into more exotic three‐dimensional structures created for the complex with the water tetramer. Evidence for concerted hydration dynamics emerges from a comparison between theory and experimental isotopic information. We evaluate the balance of intermolecular forces at play during the hydration network build up and discuss how a flexible first solvation layer may affect the switching dynamics of this class of systems.

The functional performance of a molecular photoswitch relies strongly on its ability to undergo structural changes in solution. In this context, microsolvation studies in the gas phase provide access to the conformational panorama of these systems in a size‐controlled hydrated environment. Here, we exploit this gas‐phase vantage point alongside quantum‐chemistry calculations to study the structural properties and microhydration dynamics of camphorquinone imine, a chiral molecule holding the functionality to engage in a motor‐like function upon light activation. Using molecular rotational resonance spectroscopy with supersonic jets, we detect and analyze the first‐ and second‐order water complexes of the chiral imine. Our findings reveal that initial hydration steps significantly impact the equilibrium between open (E) and closed (Z) forms, culminating in a reversal of relative stability for the switch states. Despite being captured at rotational temperatures near 1 K, we find that water molecules exhibit notable mobility due to the lack of prominent stabilizing secondary interactions. Additionally, the assignment of a key higher‐energy closed (Z) water complex provides insights into the energy required for switching between (E) and (Z) states during collisional cooling. We discuss these effects and rationalize them in terms of molecular forces and internal dynamics governing early solvation.

The functional performance of a molecular photoswitch relies strongly on its ability to undergo structural changes in solution. In this context, microsolvation studies in the gas phase provide access to the conformational panorama of these systems in a size‐controlled hydrated environment. Here, we exploit this gas‐phase vantage point alongside quantum‐chemistry calculations to study the structural properties and microhydration dynamics of camphorquinone imine, a chiral molecule holding the functionality to engage in a motor‐like function upon light activation. Using molecular rotational resonance spectroscopy with supersonic jets, we detect and analyze the first‐ and second‐order water complexes of the chiral imine. Our findings reveal that initial hydration steps significantly impact the equilibrium between open (E) and closed (Z) forms, culminating in a reversal of relative stability for the switch states. Despite being captured at rotational temperatures near 1 K, we find that water molecules exhibit notable mobility due to the lack of prominent stabilizing secondary interactions. Additionally, the assignment of a key higher‐energy closed (Z) water complex provides insights into the energy required for switching between (E) and (Z) states during collisional cooling. We discuss these effects and rationalize them in terms of molecular forces and internal dynamics governing early solvation.

Polycyclic aromatic hydrocarbons (PAHs) are widely established as ubiquitous in the interstellar medium (ISM), but considering their prevalence in harsh vacuum environments, the role of ionisation in the formation of PAH clusters is poorly understood, particularly if a chirality-dependent aggregation route is considered. Here we report on photoelectron spectroscopy experiments on [4]helicene clusters performed with a vacuum ultraviolet synchrotron beamline. Aggregates (up to the heptamer) of [4]helicene, the smallest PAH with helical chirality, were produced and investigated with a combined experimental and theoretical approach using several state-of-the-art quantum-chemical methodologies. The ionisation onsets are extracted for each cluster size from the mass-selected photoelectron spectra and compared with calculations of vertical ionisation energies. We explore the complex aggregation topologies emerging from the multitude of isomers formed through clustering of P and M, the two enantiomers of [4]helicene. The very satisfactory benchmarking between experimental ionisation onsets vs. predicted ionisation energies allows the identification of theoretically predicted potential aggregation motifs and corresponding energetic ordering of chiral clusters. Our structural models suggest that a homochiral aggregation route is energetically favoured over heterochiral arrangements with increasing cluster size, hinting at potential symmetry breaking in PAH cluster formation at the scale of small grains.

A centuries-old physics experimental apparatus, Atwood’s machine, featured in textbooks, exercise books, and web pages, concerns two hanging masses connected by