Spectroscopy and Excited-State Dynamics of Methyl Ferulate in Molecular Beams.

The spectroscopic and dynamic properties of methyl ferulate─a naturally occurring ultraviolet-protecting filter─and microsolvated methyl ferulate have been studied under molecular beam conditions using resonance-enhanced multiphoton ionization spectroscopy in combination with quantum chemical calculations. We demonstrate and rationalize how the phenyl substitution pattern affects the state ordering of the lower excited singlet state manifold and what the underlying reason is for the conformation-dependent Franck-Condon (FC) activity in the UV-excitation spectra. Studies on microsolvated methyl ferulate reveal potential coordination sites and the influence of such coordination on the spectroscopic properties.

Probing the Hidden Photoisomerization of a Symmetric Phosphaalkene Switch.

In this study, we present the synthesis and analysis of a novel, air-stable, and solvent-resistant phosphaalkene switch. Using this symmetric switch, we have demonstrated degenerate photoisomerization experimentally for the first time. With a combination of photochemical-exchange NMR spectroscopy, ultrafast transient absorption spectroscopy, and quantum chemical calculations, we elucidate the isomerization mechanism of this symmetric phosphaalkene, comparing it to two other known molecules belonging to this class.

Urocanic acid as a novel scaffold for next-gen nature-inspired sunscreens: II. Time-resolved spectroscopy under solution conditions.

In recent years the use of synthetic UV filters in commercial skincare formulations has come under considerable scrutiny. Urocanic acid is a naturally occurring UV filter that could serve as a scaffold for developing next-generation biomimetic UV filters. We have carried out time-resolved electronic and vibrational absorption studies on urocanic acid and modified variants in various solvents on timescales spanning eighteen orders of magnitude; from femtoseconds to hours.

Getting a molecular grip on the half-lives of iminothioindoxyl photoswitches.

Visible-light-operated photoswitches are of growing interest in reversibly controlling molecular processes, enabling for example the precise spatiotemporal focusing of drug activity and manipulating the properties of materials. Therefore, many research efforts have been spent on seeking control over the (photo)physical properties of photoswitches, in particular the absorption maxima and the half-life. For photopharmacological applications, photoswitches should ideally be operated by visible light in at least one direction, and feature a metastable isomer with a half-life of 0.

Modulation of the isomerization of iminothioindoxyl switches by supramolecular confinement.

Here we present the formation of an iminothioindoxyl (ITI)⊂Cage complex that retains the photochemical properties of the photoswitch within a confined environment in water. At the same time, besides ultrafast switching inside the cage, the ITI photoswitch displays an intriguing bifurcation of the excited state isomerization pathway when encapsulated.

With or without a co-solvent? highly efficient ultrafast phenanthrenequinone-electron rich alkene (PQ-ERA) photoclick reactions.

The light-induced photocycloaddition of 9,10-phenanthrenequinone (PQ) with electron-rich alkenes (ERA), known as the PQ-ERA reaction, is a highly attractive photoclick reaction characterized by its operational simplicity and high biocompatibility. One essential aspect of photoclick reactions is their high rate, however the limited solubility of PQs often requires the use of a co-solvent. Evaluating the effect of different co-solvents on the PQ-ERA reaction and their influence on the reaction rate, we discovered that sulfur-containing compounds, in particular the frequently used solubilizing co-solvent DMSO, quench the triplet state of the PQ.

All-visible-light-driven stiff-stilbene photoswitches.

Molecular photoswitches are potent tools to construct dynamic functional systems and responsive materials that can be controlled in a non-invasive manner. As P-type photoswitches, stiff-stilbenes attract increasing interest, owing to their superiority in quantum yield, significant geometric differences between isomers, excellent thermostability and robust switching behavior. Nevertheless, the UV-light-triggered photoisomerization of stiff-stilbenes has been a main drawback for decades as UV light is potentially harmful and has low penetration depth.

The infrared absorption spectrum of phenylacetylene and its deuterated isotopologue in the mid- to far-IR.

Anharmonicity strongly influences the absorption and emission spectra of polycyclic aromatic hydrocarbon (PAH) molecules. Here, IR-UV ion-dip spectroscopy experiments together with detailed anharmonic computations reveal the presence of fundamental, overtone, as well as 2- and 3-quanta combination band transitions in the far- and mid-infrared absorption spectra of phenylacetylene and its singly deuterated isotopologue. Strong absorption features in the 400-900 cm-1 range originate from CH(D) in-plane and out-of-plane wags and bends, as well as bending motions including the C≡C and CH bonds of the acetylene substituent and the aromatic ring.

Structural Elucidation of Agrochemical Metabolic Transformation Products Based on Infrared Ion Spectroscopy to Improve In Silico Toxicity Assessment.

Toxicological assessments of newly developed agrochemical agents consider chemical modifications and their metabolic and biotransformation products. To carry out an in silico hazard assessment, understanding the type of chemical modification and its location on the original compound can greatly enhance the reliability of the evaluation. Here, we present and apply a method based on liquid chromatography-mass spectrometry (LC-MS) enhanced with infrared ion spectroscopy (IRIS) to better delineate the molecular structures of transformation products before in silico toxicology evaluation.

Molecular beam laser spectroscopic studies of the photoactive properties of resveratrol.

Resonance Enhanced MultiPhoton Ionization spectroscopic techniques coupled with laser desorption and supersonic cooling have been employed to elucidate the photoactive properties of resveratrol. The observed excitation spectra give evidence for an internal-energy dependent trans-cis isomerisation pathway in the electronically excited state, while pump-probe studies show dynamics that are in line with what is known for the parent compound, trans-stilbene. Similar studies have been performed on a derivative of resveratrol with methoxy instead of hydroxy groups, a compound aimed to reduce previously observed photodegradation pathways of resveratrol.

Mechanistic Basis for Red Light Switching of Azonium Ions.

Azonium ions formed by the protonation of tetra--methoxy-substituted aminoazobenzenes photoisomerize with red light under physiological conditions. This property makes them attractive as molecular tools for the photocontrol of physiological processes, for example, in photopharmacology. However, a mechanistic understanding of the photoisomerization process and subsequent thermal relaxation is necessary for the rational application of these compounds as well as for guiding the design of derivatives with improved properties.

Correction: A visible-light-driven molecular motor based on barbituric acid.

[This corrects the article DOI: 10.1039/D3SC03090C.].

A visible-light-driven molecular motor based on barbituric acid.

We present a class of visible-light-driven molecular motors based on barbituric acid. Due to a serendipitous reactivity we observed during their synthesis, these motors possess a tertiary stereogenic centre on the upper half, characterised by a hydroxy group. Using a combination of femto- and nanosecond transient absorption spectroscopy, molecular dynamics simulations and low-temperature H NMR experiments we found that these motors operate similarly to push-pull second-generation overcrowded alkene-based molecular motors.

An Artificial Intelligence Approach for Tackling Conformational Energy Uncertainties in Chiroptical Spectroscopies.

Determination of the absolute configuration of chiral molecules is a prerequisite for obtaining a fundamental understanding in any chirality-related field. The interaction with polarised light has proven to be a powerful means to determine this absolute configuration, but its application rests on the comparison between experimental and computed spectra for which the inherent uncertainty in conformational Boltzmann factors has proven to be extremely hard to tackle. Here we present a novel approach that overcomes this issue by combining a genetic algorithm that identifies the relevant conformers by accounting for the uncertainties in DFT relative energies, and a hierarchical clustering algorithm that analyses the trends in the spectra of the considered conformers and identifies on-the-fly when a given chiroptical technique is not able to make reliable predictions.

Characterization of Solar Radiation-Induced Degradation Products of the Plant Sunscreen Sinapoyl Malate.

Agricultural activities at lower temperatures lead to lower yields due to reduced plant growth. Applying photomolecular heater agrochemicals could boost yields under these conditions, but UV-induced degradation of these compounds needs to be assessed. In this study, we employ liquid chromatography-mass spectrometry (LC-MS) coupled with infrared ion spectroscopy (IRIS) to detect and identify the degradation products generated upon simulated solar irradiation of sinapoyl malate, a proposed photomolecular heater/UV filter compound.

Polycyclic aromatic hydrocarbon growth in a benzene discharge explored by IR-UV action spectroscopy.

Infrared signatures of polycyclic aromatic hydrocarbons (PAHs) are detected towards many phases of stellar evolution. PAHs are major players in the carbon chemistry of the interstellar medium, forming the connection between small hydrocarbons and large fullerenes. However, as details on the formation of PAHs in these environments are still unclear, modeling their abundance and chemistry has remained far from trivial.

Controlling forward and backward rotary molecular motion on demand.

Synthetic molecular machines hold tremendous potential to revolutionize chemical and materials sciences. Their autonomous motion controlled by external stimuli allows to develop smart materials whose properties can be adapted on command. For the realisation of more complex molecular machines, it is crucial to design building blocks whose properties can be controlled by multiple orthogonal stimuli.

Towards developing novel and sustainable molecular light-to-heat converters.

Light-to-heat conversion materials generate great interest due to their widespread applications, notable exemplars being solar energy harvesting and photoprotection. Another more recently identified potential application for such materials is in molecular heaters for agriculture, whose function is to protect crops from extreme cold weather and extend both the growing season and the geographic areas capable of supporting growth, all of which could help reduce food security challenges. To address this demand, a new series of phenolic-based barbituric absorbers of ultraviolet (UV) radiation has been designed and synthesised in a sustainable manner.

Temperature-dependent modulation by biaryl-based monomers of the chain length and morphology of biphenyl-based supramolecular polymers.

Supramolecular copolymerizations offer attractive options to introduce structural and functional diversity in supramolecular polymer materials. Yet, general principles and structure-property relationships for rational comonomer design remain lacking. Here, we report on the supramolecular (co)aggregation of a phenylpyridine and bipyridine derivative of a recently reported biphenyl tetracarboxamide-based monomer.

Phenylimino Indolinone: A Green-Light-Responsive T-Type Photoswitch Exhibiting Negative Photochromism.

Imines are photoaddressable motifs useful in the development of new generations of molecular switches, but their operation with low-energy photons and control over isomer stability remain challenging. Based on a computational design, we developed phenylimino indolinone (PIO), a green-light-addressable T-type photoswitch showing negative photochromism. The isomerization behavior of this photoactuator of the iminothioindoxyl (ITI) class was studied using time-resolved spectroscopies on time scales from femtoseconds to the steady state and by quantum-chemical analyses.

Tailoring the optical and dynamic properties of iminothioindoxyl photoswitches through acidochromism.

Multi-responsive functional molecules are key for obtaining user-defined control of the properties and functions of chemical and biological systems. In this respect, pH-responsive photochromes, whose switching can be directed with light and acid-base equilibria, have emerged as highly attractive molecular units. The challenge in their design comes from the need to accommodate application-defined boundary conditions for both light- and protonation-responsivity.