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Confining molecules within well-defined nanosized spaces can profoundly alter their physicochemical characteristics. For example, the controlled aggregation of chromophores into discrete oligomers has been shown to tune their optical properties whereas encapsulation of reactive species within molecular hosts can increase their stability. The resazurin/resorufin pair has been widely used for detecting redox processes in biological settings; yet, how tight confinement affects the properties of these two dyes remains to be explored. Here, we show that a flexible PdII6L4 coordination cage can efficiently encapsulate both resorufin and resazurin in the form of dimers, dramatically modulating their optical properties. Furthermore, binding within the cage significantly decreases the reduction rate of resazurin to resorufin, and the rate of the subsequent reduction of resorufin to dihydroresorufin. During our studies, we also found that upon dilution, the PdII6L4 cage disassembles to afford PdII2L2 species, which lacks the ability to form inclusion complexes – a process that can be reversed upon the addition of the strongly binding resorufin/resazurin guests. We expect that the herein disclosed ability of a water-soluble cage to reversibly modulate the optical and chemical properties of a molecular redox probe will expand the versatility of synthetic fluorescent probes in biologically relevant environments.

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Properties of 1,2 bis (4 [(E) 2 quinoline 2 vinyl)phenoxymethyl)benzene, a bis(styrylquino line) dyad SoS, in which two styrylquinoline fragments (SQ) are linked by o xylylene bridge, have been inves tigated. Photoisomerization of the SQ fragment in the bichromophoric dyad occurs as efficiently as in the monochromophoric model compound 2 (4 methoxystyryl)quinoline MeSQ. Along with photoisomeriza tion, [2 + 2] photocycloaddition occurs affording tetrasubstituted cyclobutane. According to the quantum chemical DFT calculations, this reaction is assisted by preorganizing action of o xylylene group orienting the two SQ fragments in the dyad in the head to head position.

Herein, we report on a dual-color, photoswitchable donoracceptor nanosystem based on quantum dots (QD) and an anthryl quinolyl ethylene photoactive functional ligand (AQE-FL), in which a carboxylic group is used to anchor AQE-FL to QD. Photophysical and photochemical properties of the resulting photoswitchable QD system (psQD) were studied by steady state and time-resolved spectroscopic methods. Efficient Förster resonance energy transfer (FRET) from QD to AQE-FL was shown. Applicability of the Stern-Volmer formalism (with a subdivision into static and dynamic quenching) to the psQD studied is discussed. The spectral overlap integrals of QD emission and trans-and cis-AQE-FL isomers absorption differ by 3 times that which is used for controlling the FRET efficiency. Consequently, the psQD emission is redistributed between the QD (417 nm) and AQE (520 nm) channels, i. e. dual-color fluorescent switching between two observable states without the "off" state is recorded.