Fluorescence Switching with a Photochromic Auxochrome

We synthesized a photoswitchable fluorescent probe incorporating a coumarin fluorophore and an oxazine photochrome within the same molecular skeleton. The visible illumination of this fluorophore−photochrome dyad results in the excitation of the fluorescent component only if the photochromic element is activated with ultraviolet irradiation. Indeed, the photoinduced opening of the oxazine ring bathochromically shifts the absorption of the coumarin fragment sufficiently to encourage its visible excitation with concomitant fluorescence. These operating principles translate into fluorescence photoactivation with good contrast ratio and brightness as well as short fluorescence lifetime. The modular character and relative simplicity of this synthetic strategy for the assembly of photoswitchable constructs might evolve into a general design logic for the photoregulation of the electronic structure of a given chromophore with a photochromic auxochrome

Fast Fluorescence Photoswitching in a BODIPY−Oxazine Dyad with Excellent Fatigue Resistance

We synthesized a photoswitchable fluorescent probe incorporating a BODIPY fluorophore and an oxazine photochrome within the same molecular skeleton. The selective excitation of the BODIPY component at visible wavelengths is accompanied by the emission of light in the form of fluorescence. However, the illumination of the sample at ultraviolet wavelengths opens reversibly the oxazine ring and activates the intramolecular transfer of energy from the fluorophore to the photochrome with concomitant fluorescence quenching. As a result, the emission of this fluorophore−photochrome dyad can be modulated on a microsecond time scale for hundreds of switching cycles, relying on the interplay of two exciting beams. Our operating principles for fast fluorescence photoswitching with excellent fatigue resistance can lead to the development of valuable probes for the super-resolution imaging of biological samples

Polystyrene Nanofiber Materials for Visible-Light-Driven Dual Antibacterial Action via Simultaneous Photogeneration of NO and O₂(¹Δ_g)

This contribution reports on the preparation, characterization, and biological evaluation of electrospun polystyrene nanofiber materials engineered with a covalently grafted NO photodonor and ionically entangled tetracationic porphyrin and phthalocyanine photosensitizers. These photofunctional materials exhibit an effective and simultaneous photogeneration of two antibacterial species such as nitric oxide (NO) and singlet oxygen, O₂(¹Δ_g) under illumination with visible light, as demonstrated by their direct detection using amperometric and time-resolved spectroscopic techniques. Dual-mode photoantibacterial action is demonstrated by antibacterial tests carried out on Escherichia coli

NO Photoreleaser-Deoxyadenosine and -Bile Acid Derivative Bioconjugates as Novel Potential Photochemotherapeutics

This contribution reports the synthesis of some novel bioconjugates with anticancer activity and able to release nitric oxide (NO) under visible light excitation. The 4-nitro-2-(trifluoromethyl)­aniline derivative, a suitable NO photodonor, was conjugated with 2′-deoxyadenosine and urso- and cheno-deoxycholic acid derivatives, through a thioalkylic chain or the 4-alkyl-1,2,3-triazole moiety. Photochemical experiments demonstrated the effective release of NO from 2′-deoxyadenosine and ursodeoxycholic acid conjugates under the exclusive control of visible light inputs. Studies for the <i>in vitro</i> antiproliferative activity against leukemic K562 and colon carcinoma HCT116 cell lines are reported for all the compounds as well as a case study of photocytotoxicity against HCT116

Light-Regulated NO Release as a Novel Strategy To Overcome Doxorubicin Multidrug Resistance

Nitric oxide (NO) release from a suitable NO photodonor (<b>NOP</b>) can be fine-tuned by visible light stimuli at doses that are not toxic to cells but that inhibit several efflux pumps; these are mainly responsible for the multidrug resistance of the anticancer agent doxorubicin (<b>DOX</b>). The strategy may thus increase <b>DOX</b> toxicity against resistant cancer cells. Moreover, a novel molecular hybrid covalently joining <b>DOX</b> and <b>NOP</b> showed similar increased toxicity toward resistant cancer cells and, in addition, lower cardiotoxicity than <b>DOX</b>. This opens new and underexplored approaches to overcoming the main therapeutic drawbacks of this chemotherapeutic based on light-controlled release of NO