Despite the outstanding relevance of proton transfer reactions, investigations of the solvent dependence on the elementary step are scarce. We present here a probe system of a pyrene-based photoacid and a phosphine oxide, which forms stable hydrogen-bonded complexes in aprotic solvents of a broad polarity range. By using a photoacid, an excitedstate proton transfer (ESPT) along the hydrogen bond can be triggered by a photon and observed via fluorescence spectroscopy. Two emission bands could be identified and assigned to the complexed photoacid (CPX) and the hydrogen-bonded ion pair (HBIP) by a solvatochromism analysis based on the Lippert−Mataga model. The latter indicates that the difference in the change of the permanent dipole moment of the two species upon excitation is ∼3 D. This implies a displacement of the acidic hydrogen by ∼65 pm, which is in quantitative agreement with a change of the hydrogen bond configuration from O−H

Permethylated disila[2]metallocenophanes of silicon, germanium, tin, lead, 2 a–d, (tetrelocenophanes) and antimony, 3 a,b, (pnictogenocenophanes) are described. In the case of antimony, a chloro‐substituted stibonocenophane, 3 a, as well as cationic stibonocenophanium tetrachloroaluminate and tetraphenylborate salts, 3 b[X] (X=[AlCl4], [BPh4]), were synthesized. These represent the first examples of metallocenophanes of any Group 15 element. All compounds were studied in solution and in the solid state. Without exception the ansa‐bridge exerts a strong influence on the bending angle of the two Cp‐ligands. For disila[2]plumbocenophane, 2 d, its reactivity towards Group 15 halides was probed. Treatment of disila[2]plumbocenophane, 2 d, with two equivalents of phosphorus(III) chloride or arsenic(III) chloride, results in a ring‐opening reaction and gives the bis(dihalopnictogenyl)‐substituted products, 4 a,b.

The concept of metallocenophanes has been well established for transition metals for a long time. Expanding this concept to p‐block elements, the synthesis of sila[2]tetrelocenophanes, with examples for germanium, tin, and lead as the central atoms, was explored. For the first time, the crystal structures of such compounds were obtained, and they gave intriguing insight into the geometry of this almost unexplored class of low‐valent main‐group molecules.

Intermolecular Proton Transfer (PT) dynamics can be best studied by optical spectroscopy, which can cover the vast timescale spanned by the process. PT in a hydrogen bonding complex between a pyranine‐based photoacid and a trialkyl‐phosphine oxide is addressed. The photoreaction is traced with the help of femtosecond transient absorption and picosecond‐resolved fluorescence. Characteristic kinetics and spectra of the intervening species are isolated by global analysis and spectral decomposition of time‐resolved fluorescence. It is found that the shared proton shifts towards the phosphine site upon photoexcitation in acetonitrile. The process occurs on the sub‐picosecond timescale, essentially, under solvent control. Despite the ultrafast rate, an equilibrium between the complex and the hydrogen‐bonded ion pair (HBIP) is established. Further reaction steps are delayed to the nanosecond timescale, where formation of the excited deprotonated form is observed. The far‐reaching consistency between the various methods supports an irreversible Eigen‐Weller mechanism in the excited state.

Boronic acids are widely used for labeling catechols and carbohydrates in analytical (bio)­chemistry due to their high binding affinities for diols. Here, we present two asymmetrically substituted Bodipy dyes with a boronic acid at the β-position (BBB). We present a green-emitting BBB, gBBB, and, by expanding the conjugated system of the Bodipy core at α-position, a red-emitting rBBB. Especially, gBBB shows a bathochromic shift of the electronic spectra upon binding to saccharides and polyols, whereas the fluorescence lifetime of rBBB is more sensitive to hydroxy-ligand binding. Moreover, gBBB constantly shows higher binding affinities than rBBB, reaching K b ≈ 103 M–1 at pH 8.5 for fructose. Finally, time-resolved fluorescence anisotropy allows to distinguish the number of saccharide units of oligosaccharides as the bond along the transition dipole moment ensures that the fluorescence anisotropy only decays due to the rotational diffusion of labeled carbohydrates. β-substituted BODIPY dyes are, thus, foreseen as fluorescence anisotropy labels for macromolecule sizing, where conventional fluorophores fail to discriminate due to the chemical similarity of recognition sites.