Aurones are a class of fluorescent plant flavonoids representing biocompatible fluorophores with tuneable emission colors. In this work, a series of novel 4'-alkylthio aurones is synthesized and their steady-state and time-resolved emission is studied in solution- and solid state in combination with the single-crystal X-ray diffraction (XRD) analysis. In solution, the aurones possess virtually identical cyan fluorescence with similar parameters. In contrast, in the crystalline state, the compounds exhibit remarkably variable fluorescence characterized by complex decays allowing to divide them into three groups with (i) slow, (ii) fast, and (iii) combined slow and fast emission decay. The innovative variational analysis developed in this work reveals that the alkyl substituents alter predominantly the radiationless but not the radiative deactivation rate constant indicating that the solid-state fluorescence arises mostly from the same emitter – the alkylthio aurone monomer localized in the regions of different quenching efficiency. According to the XRD data, the conjugation or lack thereof of the S atom with the π-system of the aurone core correlates directly with the solid-state emission intensity and is governed by the structure of the alkyl substituents. Overall, the obtained results provide new important insights into the structure–property relationship of SSSE aurone fluorophores.

The crystal structure of the third isomer of cyclooctenobis-1,2,3-selenadiazoles, C 8 H 8 N 4 Se 2 , is reported. The molecule is located on a twofold rotation axis. The eight-membered ring adopts a twist-chair conformation with planar heterocycles. C—H...N hydrogen bonds connect the molecules into layers parallel to ( 1 01).

The crystal structure of the third isomer of cyclooctenobis-1,2,3-selenadiazoles, C8H8N4Se2, is reported. The mol-ecule is located on a twofold rotation axis. The eight-membered ring adopts a twist-chair conformation with planar heterocycles. C-H⋯N hy-dro-gen bonds connect the mol-ecules into layers parallel to (101).

The monoclinic unit cell of the title compound contains four mol­ecules, two A and two B. In the extended structure, the two similar conformers are connected into A-ribbons and B-ribbons. Three hydrogen bonds connect the mol­ecules within the ribbons, while π–π inter­actions between the phenyl and tetra­zole moieties of different mol­ecules connect the A and B strands; the aromatic rings are nearly coplanar.

An eight-step synthesis of a (+)-dehydrobulbispermin analog was developed. Starting from optically active 4-alkylidene-tetrahydroisoquinoline, the Eschenmoser-Claisen rearrangement enabled the introduction of the central quaternary center with complete remote stereocontrol. Subsequent iodolactonization, N-BOC group cleavage, and D-ring closure delivered the key quaternary stereotriads as present in (+)-bulbispermine and (+)-hamayne. Then, methyl lithium addition and protection of the resulting OH group allowed completion of the carbon skeleton. OTBS group removal and TEMPO oxidation afforded a ketoaldehyde, which finally underwent an intramolecular aldol condensation, building up the C ring and the alpha-crinan-11-ol tetracycle derivatives, which will be used as key intermediates in the bulbispermine and 11-hydroxyvittatine-type alpha-crinane alkaloid total syntheses.

The tricyclic molecule of the title compound, C 12 H 14 O 2 , is composed of four nearly planar subunits. Hydrogen bonds connect the ketol units to chains along the a -axis direction. The structure is further consolidated by two C—H...O hydrogen bonds, one to the carbonyl and one to the hydroxy group.

The molecules of the title compound, C 19 H 12 O 2 , adopt a saddle shape, the o -xylylene fragments are almost planar. The carbonyl group and the ether oxygen atom are located on the same side of the carbon skeleton. The molecules are arranged in strands with alternating directions.

The tricyclic molecule of the title compound, C12H14O2, is composed of four nearly planar subunits. Hydrogen bonds connect the ketol units to chains along the a-axis direction. The structure is further consolidated by two C—H...O hydrogen bonds, one to the carbonyl and one to the hydroxy group.

Two mol-ecules of the title compound, C10H16N2OSe, with a chair conformation are connected via hydrogen bonds into centrosymmetric dimers. C-H⋯O hydrogen bonds inter-connect the dimers.

Silylium ions, three‐coordinated as well as donor‐stabilized, have attracted the interest of chemists for many years, have paved its way into practical application as catalysts for organic reactions, and have contributed to the understanding of fundamental chemistry problems. Since the first carbenes have been isolated and characterized, they had and still have an ongoing enormous impact on organic as well as on inorganic and organometallic chemistry. Herein, the synthesis and complete characterization of silatranyl cations as their acetonitrile‐ respectively propionitrile‐coordinated hexachlorido antimonates is reported. Upon interaction of the former with 4‐dimethylaminopyridine (DMAP) conversion to an unprecedented carbene–type complex of antimony pentachloride occurred, nicely combining silylium and carbene chemistry.

A third isomer of cyclooctenobis-1,2,3-selenadiazoles is reported. The mol­ecule is located on a twofold rotation axis and the eight-membered ring adopts a twist-chair conformation with planar heterocycles.

In the title salt, C21H17+·ClO4−, two hydrogen bonds from the tropylium moiety and the vinyl group connect the cation with oxygen atoms of the perchlorate anion. The perchlorate anion is surrounded by three tropylium cations. The tropylium rings of the cations, which are related via a C2 axis, are mostly parallel with a short distance between the centroids.

The monoclinic unit cell of the title compound, C17H24N4O, contains four mol-ecules, two A and two B. In the extended structure, the two similar conformers are connected into A-ribbons and B-ribbons. Three hydrogen bonds connect the mol-ecules within the ribbons, while π-π inter-actions between the phenyl and tetra-zole moieties of different mol-ecules [centroid-centroid distances of 3.5288 (11) and 3.6138 (11) Å] connect the A and B strands; the aromatic rings are nearly coplanar.

Mol­ecules of the title compound, C10H16N2OSe, adopt a chair conformation and are connected via hydrogen bonds into centrosymmetric dimers. C—H⋯O hydrogen bonds inter­connect the dimers.

The molecules of the title compound, C19H12O2, adopt a saddle shape, the o-xylylene fragments are almost planar. The carbonyl group and the ether oxygen atom are located on the same side of the carbon skeleton. The molecules are arranged in strands with alternating directions.

Switching the electronic spin state in molecules by light is achieved via chemical bond reshuffling or light-induced excited spin state trapping. These procedures either require large-amplitude nuclear motions or cryogenic temperatures limiting their application in data storage or quantum computing devices. Here we show that a carbene manganese(II) complex undergoes light-induced excited spin state trapping at 141 K in solution and 112.5 K in the solid state. Irradiation quantitatively switches from low- to high-spin in solution and in the solid. The lifetime of the metastable high-spin state extrapolated from experimental data amounts to over 1 million years at 77 K. Key to success for the very long lifetime is the high reorganization energy due to high metal-ligand bond covalency, and hence, a large barrier height and width for the spin relaxation, paving the way for photo-switchable magnetic materials operating at ambient temperature.

In the title com-pound, C8H8N4Se2, two almost planar 1,2,3-selena-diazo-les are annulated to a cyclo-octa-1,4-diene with a boat-chair conformation, giving the mol-ecule a butterfly shape.

Both six-membered rings in the title bicyclo[3.3.1] system, C 8 H 13 BrO 2 , adopt a chair conformation. Hydrogen bonds from the hydroxy group to the ether bridge connect the molecules into zigzag chains: single-enantiomer chains propagating along the b -axis direction form the crystal.

In the title salt, C7H6N3O2S+·C7H5O6S-, the cation is protonated at the thia-zole N atom and the dihedral angle between the nitro group and its attached benzene ring is 3.6 (4)°. In the anion, the sulfonate group is deprotonated and the dihedral angle between the carb-oxy-lic acid grouping and its attached ring is 7.1 (4)° and an intra-molecular O-H⋯O hydrogen bond occurs. In the crystal, cation-to-anion N-H⋯O and anion-to-anion O-H⋯O hydrogen bonds link the component ions into (101) sheets. Aromatic π-π stacking and weak C-H⋯O and C-H⋯S inter-actions also occur.

In a recent communication, Collins and coworkers presented a Cu(I) complex with photocatalytic activity under red light LED conditions, mainly for singlet oxygen-driven reactions. Guided by steady-state emission measurements with 800 nm excitation, the authors suggested that the underlying mechanism for the generation of the photoexcited key species is a simultaneous two-photon absorption via a virtual state. However, such a mechanism requires pulsed laser excitation and cannot compete when a conventional one-photon excitation is also feasible with the selected excitation wavelength range. Using several spectroscopic techniques and reactivity assays under different light color and intensity conditions, we unambiguously demonstrate that a conventional one-photon excitation followed by rather inefficient singlet oxygen generation (quantum yield <5%) is responsible for the observed photoreactivity of the Cu(I) complex. In addition, we briefly summarize general mechanistic considerations, estimate typical photon densities required for a variety of two-photon mechanisms, highlight the importance of optical filters and impurities to avoid artifacts in the emission spectra, and present some guidelines for the differentiation between one- and two-photon mechanisms.