Tracking of Single Charge Carriers in a Conjugated Polymer Nanoparticle

The motion of individual charge carriers in organic nanostructures was tracked by fluorescence microscopy. A twinkling effect is observed in fluorescence microscopy of single conjugated polymer nanoparticles, that is, small displacements in the fluorescence spot of single nanoparticles of the conjugated polymer PFBT are observed over time. There is evidence that superquenching by the charge carrier induces a dark spot in the nanoparticle, which moves with the carrier, resulting in the observed displacements in the fluorescence. Zero-field mobilities of individual charge carriers consistent with highly trapped polarons were obtained from tracking experiments

Photoswitchable Nanoparticles Enable High-Resolution Cell Imaging: PULSAR Microscopy

Photoswitchable Nanoparticles Enable High-Resolution Cell Imaging: PULSAR Microscop

Antiphase Dual-Color Correlation in a Reactant–Product Pair Imparts Ultrasensitivity in Reaction-Linked Double-Photoswitching Fluorescence Imaging

A pair of reversible photochemical reactions correlates their reactant and product specifically, and such a correlation uniquely distinguishes their correlated signal from others that are not linked by this reversible reaction. Here a nanoparticle-shielded fluorophore is photodriven to undergo structural dynamics, alternating between a green-fluorescence state and a red-fluorescence state. As time elapses, the fluorophore can be in either state but not both at the same time. Thus, the red fluorescence is maximized while the green fluorescence is minimized and vice versa. Such an antiphase dual-color (AD) corelationship between the red and green fluorescence maxima as well as between their minima can be exploited to greatly improve the signal-to-noise ratio, thus enhancing the ultimate detection limit. Potential benefits of this correlation include elimination of all interferences originating from single-color dyes and signal amplification of AD photoswitching molecules by orders of magnitude

Lanthanide-Doped Luminescent Nanoparticles with Dual-Mode Color Modulation Enable Cross-Correlation Anticounterfeiting

Lanthanide-doped upconversion nanoparticles (Ln-UCNPs) hold great potential in anticounterfeiting applications owing to their salient optical properties. However, a single-mode anticounterfeiting strategy based on common Ln-UCNPs typically confronts challenges in terms of imitation based on alternatives with a similar luminescence feature. Multilevel anticounterfeiting strategies on the basis of the multicolor beaconing luminescence generated upon dual- or multimode excitation are promising for addressing such a challenge and those based on the intrinsic mutual authentication of the dynamic signals generated via distinct manipulating manners are expected to present a higher security level. Herein, we demonstrate that low-concentration Yb/Er/Tm-codoped UCNPs with optimized formulation enable modulation of luminous color by manipulating the power of a continuous-wave 980-nm laser or the pulse parameter of the pulsed laser. The crucial role of acting as the red-emission-associated transient energy trapping center that Tm3+ species plays can be attenuated by Yb3+-mediated laser-power-dependent sensitization processes. The key intermediate states associated with red and green emission states are populated and deplete via different processes with distinct rates, which enables dependence of the emission feature on the pulse parameters of the laser. The unique feature of this type of Ln-UCNPs in terms of dual-mode luminous color modulation and its potential are preliminarily verified in our proof-of-concept cross-correlation experiment, which provides a feasible modality for high-level anticounterfeiting applications in specific scenarios such as high-value marketable securities and bond certificates

Single-Chromophore-Based Therapeutic Agent Enables Green-Light-Triggered Chemotherapy and Simultaneous Photodynamic Therapy to Cancer Cells

A new type of single-chromophore-based photoactivatable prodrug (B-Cbl-3) enabling green-light-triggered chemotherapy and simultaneous photodynamic therapy with superb therapeutic efficacy was developed by conjugating a photoactive BODIPY derivative with an antitumor chlorambucil moiety. The optimized BODIPY moiety markedly enabled high efficient photogeneration of 1O2 and fluorescence emission with distinct colors before and after photorelease of chlorambucil. The preliminary biological experiment results have verified the efficient photorelease of chlorambucil from B-Cbl-3 and the huge contrast in cytotoxicity between them, superior combined therapeutic performance based on extraordinary low doses of drug and light irradiation, and ratiometric fluorescence imaging for in situ monitoring drug release. The salient superiority of B-Cbl-3 regarding alleviating the attenuation of triggering light caused by optically turbid tissue that short-wavelength lights typically encounters has also been verified

Spirooxazine to Merooxazine Interconversion in the Presence and Absence of Zinc: Approach to a Bistable Photochemical Switch

A spironaphthoxazine (SO) photoswitch was synthesized, and its photochromic behaviors were investigated. SO underwent reversible ring-opening/closure isomerization between a spirocyclic isomer (closed form) and a merocyanine (MO isomer, open form) upon ultraviolet light irradiation. For the model SO in this work, the thermal equilibrium is substantially shifted toward the spirocyclic isomer even at −30.0 °C. However, addition of zinc, as Zn(ClO4)2, exerted an important effect on the thermal reversion process from the open (MO) to the closed form (SO). Kinetic analysis showed that thermal reversion with zinc is retarded more than 13-fold, significantly improving bistability. Moreover, introduction of zinc to the spirooxazine−merooxazine (SO−MO) system resulted in a new absorption band readily distinguishable from the bands arising from spirooxazine and merooxazine. For the first time, to the best of our knowledge, the microscopic rate constants for: MO photogeneration from SO (k1), thermal reversion of MO to SO (k2), complexation of MO with zinc (k3) and for dissociation of the complex, MO−Zn (k4), as well as for the ionization equilibria of Zn(ClO4)2 have been evaluated. The preferred transoid structures of MO and those of MO−Zn derived from the preferred MO structures are considered. Although the kinetic study does not permit elucidation of the nature of zinc binding to MO to give MO−Zn, nor the precursor isomers of MO, a DFT calculational study in progress should shed light on the structure and relative stability of these essential intermediates

Spirooxazine to Merooxazine Interconversion in the Presence and Absence of Zinc: Approach to a Bistable Photochemical Switch

A spironaphthoxazine (SO) photoswitch was synthesized, and its photochromic behaviors were investigated. SO underwent reversible ring-opening/closure isomerization between a spirocyclic isomer (closed form) and a merocyanine (MO isomer, open form) upon ultraviolet light irradiation. For the model SO in this work, the thermal equilibrium is substantially shifted toward the spirocyclic isomer even at −30.0 °C. However, addition of zinc, as Zn(ClO4)2, exerted an important effect on the thermal reversion process from the open (MO) to the closed form (SO). Kinetic analysis showed that thermal reversion with zinc is retarded more than 13-fold, significantly improving bistability. Moreover, introduction of zinc to the spirooxazine−merooxazine (SO−MO) system resulted in a new absorption band readily distinguishable from the bands arising from spirooxazine and merooxazine. For the first time, to the best of our knowledge, the microscopic rate constants for: MO photogeneration from SO (k1), thermal reversion of MO to SO (k2), complexation of MO with zinc (k3) and for dissociation of the complex, MO−Zn (k4), as well as for the ionization equilibria of Zn(ClO4)2 have been evaluated. The preferred transoid structures of MO and those of MO−Zn derived from the preferred MO structures are considered. Although the kinetic study does not permit elucidation of the nature of zinc binding to MO to give MO−Zn, nor the precursor isomers of MO, a DFT calculational study in progress should shed light on the structure and relative stability of these essential intermediates

Photoswitching Near-Infrared Fluorescence from Polymer Nanoparticles Catapults Signals over the Region of Noises and Interferences for Enhanced Sensitivity

As a very sensitive technique, photoswitchable fluorescence not only gains ultrasensitivity but also imparts many novel and unexpected applications. Applications of near-infrared (NIR) fluorescence have demonstrated low background noises, high tissue-penetrating ability, and an ability to reduce photodamage to live cells. Because of these desired features, NIR-fluorescent dyes have been the premium among fluorescent dyes, and probes with photoswitchable NIR fluorescence are even more desirable for enhanced signal quality in the emerging optical imaging modalities but rarely used because they are extremely challenging to design and construct. Using a spiropyran derivative functioning as both a photoswitch and a fluorophore to launch its periodically modulated red fluorescence excitation energy into a NIR acceptor, we fabricated core–shell polymer nanoparticles exhibiting a photoswitchable fluorescence signal within the biological window (∼700–1000 nm) with a peak maximum of 776 nm. Live cells constantly synthesize new molecules, including fluorescent molecules, and also endocytose exogenous particles, including fluorescent particles. Upon excitation at different wavelengths, these fluorescent species bring about background noises and interferences covering nearly the whole visible region and therefore render many intracellular targets unaddressable. The oscillating NIR fluorescence signal with an on/off ratio of up to 67 that the polymer nanoparticles display is beyond the typical background noises and interferences, thus producing superior sharpness, reliability, and signal-to-noise ratios in cellular imaging. Taking these salient features, we anticipate that these types of nanoparticles will be useful for in vivo imaging of biological tissue and other complex specimens, where two-photon activation and excitation are used in combination with NIR-fluorescence photoswitching

Conjugated Polymer Nanoparticles Incorporating Antifade Additives for Improved Brightness and Photostability

Conjugated polymer nanoparticles with incorporated antifade agents were prepared, and ensemble and single particle measurements showed that incorporation of antifade agents effectively improves the fluorescence quantum yield and photostability of the conjugated polymer nanoparticles, likely by a combination of triplet quenching and suppression of processes involved in photogeneration of hole polarons (cations), which act as fluorescence quenchers. The photostability of conjugated polymer nanoparticles and CdSe quantum dots was compared, at both the ensemble and single particle level. The results provide confirmation of the hypothesis that quenching by photogenerated hole polarons is a key factor limiting the fluorescence quantum yield and maximum emission rate in conjugated polymer nanoparticles. Additionally, the results indicate the involvement of oxygen in photogeneration of hole polarons. The results also provide insight into the origin of quenching processes that could limit the performance of conjugated polymer devices

Spirooxazine to Merooxazine Interconversion in the Presence and Absence of Zinc: Approach to a Bistable Photochemical Switch

A spironaphthoxazine (SO) photoswitch was synthesized, and its photochromic behaviors were investigated. SO underwent reversible ring-opening/closure isomerization between a spirocyclic isomer (closed form) and a merocyanine (MO isomer, open form) upon ultraviolet light irradiation. For the model SO in this work, the thermal equilibrium is substantially shifted toward the spirocyclic isomer even at −30.0 °C. However, addition of zinc, as Zn(ClO4)2, exerted an important effect on the thermal reversion process from the open (MO) to the closed form (SO). Kinetic analysis showed that thermal reversion with zinc is retarded more than 13-fold, significantly improving bistability. Moreover, introduction of zinc to the spirooxazine−merooxazine (SO−MO) system resulted in a new absorption band readily distinguishable from the bands arising from spirooxazine and merooxazine. For the first time, to the best of our knowledge, the microscopic rate constants for: MO photogeneration from SO (k1), thermal reversion of MO to SO (k2), complexation of MO with zinc (k3) and for dissociation of the complex, MO−Zn (k4), as well as for the ionization equilibria of Zn(ClO4)2 have been evaluated. The preferred transoid structures of MO and those of MO−Zn derived from the preferred MO structures are considered. Although the kinetic study does not permit elucidation of the nature of zinc binding to MO to give MO−Zn, nor the precursor isomers of MO, a DFT calculational study in progress should shed light on the structure and relative stability of these essential intermediates