Recent advances in sustainable mechanochemical transformations of carbohydrates.

The extent of photoinduced energy-transfer between [Ru(bipy)₃]²⁺ and [Os(bipy)₃]²⁺ units attached to either end of a deca(oxoethylene) 33-atom chain can be used to show how the distribution of end-to-end distances in the ensemble of conformations changes in different solvents.

We present here the synthesis of several new isoalloxazine cyclophanes containing electroactive anthraquinones linked by aliphatic chains of different lengths. Such structural changes provide different interchromophoric orientations leading to the tuning of the rate of the photoinduced electron transfer process from the anthraquinone unit towards the isoalloxazine singlet excited state. Molecular modelling studies were undertaken in order to determine the minimal energy of the proposed structures using Monte Carlo calculations (Amber, Macromodel v.8.1). The compounds have been fully characterised by NMR spectroscopy and the solid state structures of some of the macrocycles have been elucidated. The photophysical studies have been carried out in order to investigate the influence of π–π stacking on the optical properties of the macrocycles.

The synthesis, photophysical properties and E/Z photoisomerization kinetics in solution and in the solid state of a series of three new 3-(-aryl)-1,1,1-trifluoro-3-(2-phenylhydrazono)propan-2-ones (1a–c, Scheme 1) are reported here. Both E and Z isomers were fully characterized by ¹H-, ¹³C- and ¹⁹F-NMR spectroscopy, and single crystal X-ray diffraction analysis was performed for all thermodynamically stable E isomers. The introduction of the trifluoromethyl ketone group as well as the different methyl and trifluoromethyl susbtituents on the hydrazone and the aromatic rings causes significant changes in the photoisomerization dynamics. The N–H⋯F–C(sp³) interaction is believed to have a prominent role in the stabilization of the metastable Z isomer of 1c which has a very slow back thermal isomerization rate compared to 1a and 1b. DFT calculations support the experimental findings and provide the foundation for future design of new photoswitching materials with promising applications in several technological fields.