David Reger

Electronic energy transfer (EET) between chromophores is of fundamental importance for many biological processes and optoelectronic devices. However, common models fall short in fully describing the process, especially in bichromophoric model systems with a donor and acceptor connected by a rigid linker providing perpendicular geometries. Herein, we report a novel strategy for preparing bichromophores containing adamantane or 2-(2-adamantylidene)adamantane as rigid spacers, providing a fixed distance between chromophores, and their parallel or perpendicular arrangement without chromophore rotation. New fluorophores were developed and linked via spiroatoms. Bichromophores with identical (blue-blue) or different (blue-red) chromophores were synthesized, either in orthogonal or parallel geometry. These were characterized by absorption/fluorescence spectroscopy, time-resolved fluorescence anisotropy, and fluorescence antibunching measurements. Based on the Förster point-dipole approximation, EET efficiencies were estimated by using geometrical parameters from (time-dependent) density functional calculations. For bichromophores with parallel geometry, the predicted EET efficiencies were near unity and fit the measurements. In spite of estimated values around 0.4 and 0.5, 100 % efficiency was observed also for bichromophores with orthogonal geometry. The new rigid scaffolds presented here open new possibilities for the synthesis of bichormophores with well-defined parallel or perpendicular geometry.

Novel bichromophores: A novel strategy to prepare bichromophores with fixed interchromophore distance and orientation provides ideal model compounds to study intramolecular excitation energy transfer (EET) between orthogonal or parallel arranged chromophores. Bichromophores with like (blue-blue) and unlike (blue-red) chromophores show fast and efficient EET regardless of the orthogonal or parallel geometry.

Small-molecule organoselenium-based fluorescent probes possess great capacity in understanding biological processes through the detection of various analytes such as reactive oxygen/nitrogen species (ROS/RNS), biothiols (cysteine, homocysteine and glutathione), lipid droplets, etc. Herein, we present how substituents on the BODIPY system play a significant part in the detection of biologically important analytes for in vitro conditions and live cell imaging studies. The fluorescence of the probe was quenched by 2-chloro and 6-phenyl selenium groups; the probe shows high selectivity with NaOCl among other ROS/RNS, and gives a turn-on response. The maximum fluorescence intensity is attained within ≈1–2 min with a low detection limit (19.6 nm), and shows a ≈110-fold fluorescence enhancement compared to signals generated for other ROS/RNS. Surprisingly, in live cell experiments, the probe specifically located and accumulated in lipid droplets, and showed a fluorescence turn-on response. We believe this turn-on response occurred because of aggregation-induced emission (AIE), which surprisingly occurred only by introducing one lipophilic mesityl group at the meso position of the BODIPY.

Body? Pie? No, it′s BODIPY! Substituents on boron-dipyrromethene (BODIPY) have been shown to play significant roles for the detection of biologically important analytes under in vitro conditions and in live cell imaging studies. The probe shows a selective and sensitive turn-on response with NaOCl over other reactive oxygen/nitrogen species (ROS/RNS) in vitro. Surprisingly, in live cell experiments, the probe specifically accumulates in lipid droplets and shows fluorescence turn-on responses because of aggregation-induced emission (AIE) owing to the lipophilic mesityl group at the meso position of the BODIPY.

Hexaarylbenzene–porphyrin scaffolds were prepared by means of a Diels-Alder reaction. In the cover image, the mountains and shooting stars represent the statistical product distribution, which is a useful calibrant for mass spectrometry. The strong red luminescence of the conjugates is highlighted by the red moon. The graphene landscape stands for the conversion to π–extended porphyrin conjugates. More information can be found in the Communication by T. Drewello, N. Jux, et al. (DOI: 10.1002/chem.201603789).

The water-mediated, metal-free, 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) promoted oxidative [3+2] cycloaddition of organic azides with electron-deficient terminal and internal olefins was explored. A library of 1,4-disubstituted and 1,4,5-trisubstituted-1,2,3-triazoles were synthesized in moderate to excellent yields. This method was also found to be compatible not only with open-chain olefins but also with cyclic olefins.

A 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) promoted oxidative [3+2] cycloaddition of organic azides with electron-deficient internal, terminal, and cyclic olefins is reported in aqueous medium. A diverse array of substituted 1,2,3-triazoles are synthesized in moderate to excellent yields.