This Minireview provides a critical account of the development of allene-containing advanced functional materials, starting with the design and synthesis of stable and enantiopure building blocks. A variety of systems, including shape-persistent macrocycles, foldamers, polymers, charge-transfer chromophores, dendrimers, liquid crystals, and redox-switchable chiral chromophores are discussed from the viewpoint of their syntheses, properties, and potential applications. The goal of this Minireview is to inspire new uses of enantiopure allenes for the rational design of advanced materials.

The first near-infrared fluorescent turn-on sensor for the detection of nitroxyl (HNO), the one-electron reduced form of nitric oxide (NO), is reported. The new copper-based probe, CuDHX1, contains a dihydroxanthene (DHX) fluorophore and a cyclam derivative as a Cu(II) binding site. Upon reaction with HNO, CuDHX1 displays a five-fold fluorescence turn-on in cuvettes and is selective for HNO over thiols and reactive nitrogen and oxygen species. CuDHX1 can detect exogenously applied HNO in live mammalian cells and in conjunction with the zinc-specific, green-fluorescent sensor ZP1 can perform multicolor/multianalyte microscopic imaging. These studies reveal that HNO treatment elicits an increase in the concentration of intracellular mobile zinc.

Dedicated to Prof. Dr. Roeland J. M. Nolte on the occasion of his 65th birthday Chiral allenes attract increasing interest owing to the development of improved syntheses and their emerging use in pharmaceuticals. [1] While strained small-ring allenes have been investigated in greater detail for their theoretical properties and their limits of stability and isolability, [2] allenic macrocycles, in particular shape-persistent ones, [3] are mostly unknown. [4] The scarcity of allenic macrocycles is rather surprising in view of the opportunities for creating new nonplanar, chiral topologies and for developing new chiral host molecules. The first allenic macrocycle known was a [3 4 ]cyclophane, reported by Krause and co-workers, [5] in which four p-phenylene moieties are bridged by four 1,3dimethylallene-1,3-diyl linkers and which was isolated as a mixture of several stereoisomers. Fallis and co-workers reported the preparation of the first optically active allenophanes. [6] Despite their elegant methodologies , clear proof of the enantiomeric purity of the final compounds was not provided. Furthermore, the absolute configuration of the allene moieties was not unambiguously determined, but only inferred from the reaction mechanism.In our group, we have shown that di-tert-butyl-diethynylallenes (DEAs) are stable chiral building blocks. [7] Racemic mixtures of DEAs were converted into stereoisomeric mixtures of an alleno-acetylenic macrocycle and an allenophane. All diastereoisomers were separated and characterized, [8] but the enantiomers were not resolved. In this sense, much information concerning the structural, chiroptical, and electronic properties of chiral allenic macrocycles is still missing.A deeper understanding of a chiroptical response, obtained from electronic circular dichroism (CD) spectros-copy, [9] can be accomplished by full CD calculations using quantum-mechanical methods. Such calculations provide more complex information regarding the assignment of Cotton effects to specific transitions, determination of absolute configuration, and even investigation of conformational preferences. [10] Nevertheless, to relate the chiroptical properties to structural and electronic features, conformationally stable compounds are desirable.Macrocyclization of a DEA building block by acetylenic homocoupling, following the three-step protocol shown in Scheme 1, is expected to yield the alleno-acetylenic tetramer macrocycle 1. When the racemic DEA derivative (AE )-2 is used, the cyclization affords six stereoisomers of macrocycle 1, including two racemates and two achiral diastereoisomers. The two racemates are the D 4 -symmetric (all the tert-butyl

A dual-activatable, fluorogenic probe was developed to sense esterase activity with single-molecule resolution. Without enzymatic pre-activation, the diazoindanone-based probe has an electron-poor core and, upon irradiation, undergoes Wolff rearrangement to give a ring-expanded xanthene core that is nonemissive. If the probe is pre-activated by carboxylesterases, the tricyclic core becomes electron-rich, and the photoinduced Wolff rearrangement produces a highly emissive rhodol dye. Live-cell and solution studies confirmed the selectivity of the probe and revealed that the photoactivated dye does not diffuse away from the original location of activation because the intermediate ketene forms a covalent bond with surrounding macromolecules. Single-molecule localization microscopy was used to reconstruct a super-resolved image of esterase activity. These single-molecule images of enzymatic activity changed significantly upon treatment of the cells with inhibitors of human carboxylesterase I and II, both in terms of total number of signals and intracellular distribution. This proof-of-principle study introduces a sensing mechanism for single-molecule detection of enzymatic activity that could be applied to many other biologically relevant targets.

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The efficiency of photoactivatable coumarins in water has been enhanced by substitution with azetidine.

10567 COMMUNICATION1,3-Diethynylallenes ture. Purification by FC on silica gel (hexane for 1 a and hexane/10 % AcOEt for 1 b) gave colorless oils.

New enantiomerically pure alleno-acetylenic macrocycles were prepared by oxidative homocoupling of optically active 1,3-diethynylallenes. Enantiomer separation resulted from a combined strategy of synthesis and chiral HPLC techniques. Two other achiral stereoisomers were also isolated and fully characterized. In addition, the X-ray structures of the chiral D(4)- and C(2)-symmetric macrocycles are reported. The chiroptical properties of these macrocycles are discussed on the basis of quantum chemical calculations, by using the CAM-B3LYP functional. Studies were carried out to investigate the vibronic fine structure observed experimentally in the UV/Vis and CD spectra. The origin of the intense chiroptical response of the chiral alleno-acetylenic macrocycles is explained by considering the topology of the molecular orbitals involved, thus relating electronic properties to structural features. Further analysis of the canonical molecular orbitals and the electron localization function (ELF) shows that these macrocycles belong to a relatively rare class of highly stable and formally anti-aromatic Hückel compounds.