Stiff-Stilbene Photoswitches: From Fundamental Studies to Emergent Applications.

Stiff-stilbene, a sterically restricted fused ring analogue of stilbene, has been regularly used as a model compound in theoretical studies of stilbene photoisomerization. Lately, owing to its excellent photoswitching properties, it is increasingly being applied to reversibly control the properties and function of chemical as well as biological systems. Stiff-stilbene photoswitches possess a number of advantageous properties including a high quantum yield for photoisomerization and a high thermal stability. Furthermore, they undergo a large geometrical change upon isomerization and their synthesis is straightforward. Herein, we provide an overview of the basic properties of stiff-stilbene and of recent applications in supramolecular chemistry, catalysis, and biological systems.

On the Transition from a Biomimetic Molecular Switch to a Rotary Molecular Motor.

The experimental investigation of the unidirectional motion characterizing the photoisomerization of single-molecule rotary motors requires accessible lab prototypes featuring an electronic circular dichroism (ECD) signal that is sensitive to the geometrical and electronic changes occurring during an ultrafast reactive process. Here we report a combined experimental/computational study of a candidate obtained via the asymmetrization of a light-driven biomimetic molecular switch. We show that the achieved motor has an ECD band that is remarkably sensitive to the isomerization motion, and it is therefore suitable for time-resolved ECD studies. However, we also find that, unexpectedly, the synthesized motor isomerizes on a time scale longer than the subpicosecond time measured for the achiral parent, a result that points to alternative candidates conserving a high reaction speed.

"Internal and External Combined" Nonradiative Decay-Based Nanoagents for Photoacoustic Image-Guided Highly Efficient Photothermal Therapy.

Rational manipulation of nonradiative decay channels is of crucial significance to improve photothermal conversion efficiency (PCE) and design photothermal agents. We first used the "internal and external combined" nonradiative decay strategy to enhance PCE. Specifically, organic IR-Y6 NPs with strong NIR absorption and high molar extinction coefficient were prepared and characterized. By means of TD-DFT calculations and fs-TA spectroscopy, the dual nonradiative decay channels composed of the free rotor (external strategy) and ultrafast dark excited states (DESs) between S0 and S1 states (internal strategy) were proved, which significantly enhanced PCE, up to 66%. IR-Y6 NPs were applied to a mice tumor model for photoacoustic image-guided photothermal therapy, showing complete tumor ablation ability and good biocompatibility for the normal organs. This work is of significance to deeply understand the nonradiation decay mechanism and rational design of high-performance PTT agents.

A Molecular Logic Gate Enables Single-Molecule Imaging and Tracking of Lipids in Intracellular Domains.

Photoactivatable dyes enable single-molecule imaging and tracking in biology. Despite progress in the development of new fluorophores and labeling strategies, many intracellular compartments remain difficult to image beyond the limit of diffraction in living cells. For example, lipid domains, e.g., membranes and droplets, remain difficult to image with nanometric resolution. To visualize these challenging subcellular targets, it is necessary to develop new fluorescent molecular devices beyond simple on/off switches. Here, we report a fluorogenic molecular logic gate that can be used to image single molecules associated with lipid domains, most notably droplets, with excellent specificity. This probe requires the subsequent action of light, a lipophilic environment, and a competent nucleophile to produce a fluorescent product. The combination of these inputs results in a probe that can be used to image the boundary of lipid droplets in three dimensions with resolution beyond the limit of diffraction. Moreover, this probe enables single-molecule tracking of lipid trafficking between droplets and the endoplasmic reticulum.

Kinetics of nitromusk compounds degradation in water by ultraviolet radiation and hydrogen peroxide.

The photodegradation of five representative nitromusk compounds in water has been performed in a stirred batch photoreactor with a UV low-pressure immersed mercury lamp, at constant temperature and different doses of hydrogen peroxide. The rate constants have been calculated on the basis of experimental data and a postulated first-order kinetic model. The rate constants, at 298 K and a dose of 1.1746 micromol l(-1) H2O2 ranges from 0.3567 x 10(-3) s(-1) for musk tibetene, to 1.785 x 10(-3) s(-1) for musk ambrette.