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The design of bright short-wave infrared fluorophores remains a grand challenge. Here we investigate the impact of deuteration on the properties in a series of heptamethine dyes, the absorption of which spans near-infrared and SWIR regions. We demonstrate that it is a generally applicable strategy that leads to enhanced quantum yields of fluorescence, longer-lived singlet excited states and suppressed rates of non-radiative deactivation processes. [ABSTRACT FROM AUTHOR]

Two new classes of near‐infrared molecular probes were prepared and shown to exhibit "turn on" fluorescence when cleaved by the nitroreductase enzyme, a well‐known biomarker of cell hypoxia. The fluorescent probes are heptamethine cyanine dyes with a central 4'‐carboxylic ester group on the heptamethine chain that is converted by a self‐immolative fragmentation mechanism to a 4'‐caboxylate group that greatly enhances the fluorescence brightness. Each compound was prepared by ring opening of a Zincke salt. The chemical structures have either terminal benzoindolinenes or propargyloxy auxochromes, which provide favorable red‐shifted absorption/emission wavelengths and a hyperchromic effect that enhances the photon output when excited by 808 nm light. A fluorescent probe with terminal propargyloxy‐indolenines exhibited less self‐aggregation and was rapidly activated by nitroreductase with large "turn on" fluorescence; thus, it is the preferred choice for translation towards in vivo applications. [ABSTRACT FROM AUTHOR]

The sensitization of lanthanide-doped upconversion nanocrystals (UCNCs) using organic dyes with a broad and intense optical absorption is an interesting approach for efficient excitation-energy harvesting and enhancing the upconversion luminescence of such UCNCs. In this work, an ultrasmall (∼6.5 nm in diameter) β-NaGdF4:Yb3+,Er3+ core and related core@shell UCNCs were sensitized using six NIR-excitable cyanine dyes with a wide range of functional groups and optical properties. The greatest UC enhancement of 680-times was observed for the conjugate between the Cy 754 dye and NaGdF4:Yb3+,Er3+@NaGdF4:10%Yb3+,30%Nd3+ core@shell UCNCs excited using a 754 nm laser. The enhancement was estimated relative to NaGdF4:Yb3+,Er3+@NaGdF4:10%Yb3+,30%Nd3+ core@shell UCNCs capped with oleic acid and excited using a similar intensity (75 W cm−2) of a 980 nm laser. UC intensity measurements for identical dye-sensitized UCNCs carried out in methanol and in deuterated methanol under argon, as well as in air, allowed us to reveal the connection of the dye triplet states with UCNC sensitization as well as of the hydroxyl groups with quenching of the excited states of lanthanide ions. For UCNCs dispersed in methanol, the strong quenching UC luminescence was always observed, including core@shell UCNCs (with a shell of ∼2 nm). A strong influence of the triplet states of the dyes was observed for the two dyes Cy 754 and Cy 792 that bind firmly to UCNCs and allow the distances between the dye and the UCNC to be reduced, whereas the contribution of this sensitization pathway is very insignificant for Cy 740 and Cy 784 dyes that bind weakly to UCNCs. [ABSTRACT FROM AUTHOR]

Artificial molecular motors hold great promise for application in responsive functional materials as well as to control the properties of biohybrid systems. Herein a strategy is reported to modulate the rotation of light-driven molecular motors. That is, the rotary speed of a molecular motor, functionalized with a biphenol moiety, could be decreased in situ by non-covalent substrate binding, as was established by 1H NMR and UV/Vis spectroscopy. These findings constitute an important step in the development of multi-responsive molecular machinery. [ABSTRACT FROM AUTHOR]

Switching systems operating in a cooperative manner capable of converting light energy into mechanical motion are of great interest for optical devices, data storage, nanoscale energy converters and molecular sensing. Herein, photoswitchable monolayers were formed at the air-water interface from either a pure bis(thiaxanthylidene)-based photoswitchable amphiphile or from a mixture of the photoswitchable amphiphile with a conventional lipid dipalmitoylphosphatidylcholine (DPPC). Efficient photoisomerization of the anti-folded to syn-folded geometry of the amphiphile's central core induces changes in the surface pressure in either direction, depending on the initial molecular density. Additionally, the switching behavior can be regulated in the presence of DPPC, which influences the packing of the molecules, thereby controlling the transformation upon irradiation. Bis(thiaxanthylidene)-based photoswitchable monolayers provide a promising system to explore cooperativity and amplification of motion. [ABSTRACT FROM AUTHOR]

Regulation of pH plays an essential role in orchestrating the delicate cellular machinery responsible for life as we know it. Its abnormal values are indicative of aberrant cellular behavior and associated with pathologies including cancer progression or solid tumors. Here, we report a series of bent and linear aminobenzocoumarins decorated with different substituents. We investigate their photophysical properties and demonstrate that the probes display strong pH-responsive fluorescence "turn on" behavior in highly acidic environments, with enhancement up to 300-fold. In combination with their low cytotoxicity, this behavior enabled their application in bioimaging of acidic lysosomes in live human cells. We believe that these molecules serve as attractive lead structures for future rational design of novel biocompatible fluorescent pH probes., (© 2024 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Near-infrared light (NIR; 650-900 nm) offers unparalleled advantages as a biocompatible stimulus. The development of photocages that operate in this region represents a fundamental challenge due to the low energy of the excitation light. Herein, we repurpose cyanine dyes into photocages that are available on a multigram scale in three steps and efficiently release carboxylic acids in aqueous media upon irradiation with NIR light up to 820 nm. The photouncaging process is examined using several techniques, providing evidence that it proceeds via photooxidative pathway. We demonstrate the practical utility in live HeLa cells by delivery and release of the carboxylic acid cargo, that was otherwise not uptaken by cells in its free form. In combination with modularity of the cyanine scaffold, the realization of these accessible photocages will fully unleash the potential of the emerging field of NIR-photoactivation and facilitate its widespread adoption outside the photochemistry community., (© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Carbon monoxide (CO) is an endogenous signaling molecule that controls a number of physiological processes. To circumvent the inherent toxicity of CO, light-activated CO-releasing molecules (photoCORMs) have emerged as an alternative for its administration. However, their wider application requires photoactivation using biologically benign visible and near-infrared (NIR) light. In this work, a strategy to access such photoCORMs by fusing two CO-releasing flavonol moieties with a NIR-absorbing cyanine dye is presented. These hybrids liberate two molecules of CO in high chemical yields upon activation with NIR light up to 820 nm and exhibit excellent uncaging cross-sections, which surpass the state-of-the-art by two orders of magnitude. Furthermore, the biocompatibility and applicability of the system in vitro and in vivo are demonstrated, and a mechanism of CO release is proposed. It is hoped that this strategy will stimulate the discovery of new classes of photoCORMs and accelerate the translation of CO-based phototherapy into practice., (© 2020 The Authors. Published by Wiley-VCH GmbH.)

Artificial molecular motors hold great promise for application in responsive functional materials as well as to control the properties of biohybrid systems. Herein a strategy is reported to modulate the rotation of light-driven molecular motors. That is, the rotary speed of a molecular motor, functionalized with a biphenol moiety, could be decreased in situ by non-covalent substrate binding, as was established by 1 H NMR and UV/Vis spectroscopy. These findings constitute an important step in the development of multi-responsive molecular machinery., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A series of unprecedented second generation molecular motors featuring a quaternary stereogenic center substituted with a fluorine atom has been synthesized. It is demonstrated that a seemingly benign replacement of the stereogenic hydrogen for a fluorine atom, regarded as a common substituent in pharmacology, resulted in a dramatic change in the energetic profile of thermal helix inversion. The barrier for the thermal helix inversion was found to increase considerably (by 20-30 kJ mol -1 ), presumably due to destabilization of the transition state by increased steric hindrance when the fluorine atom is forced to pass over the lower half of the motor. This results in the activation barrier for the thermal helix inversion to be higher than the barrier for backward thermal E-Z isomerization, impairing the motor function. A fluorine-substituted motor capable of performing unidirectional rotation is successfully prepared when these limitations are considered in the design phase., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)