Switching Photon Upconversion by Using Photofluorochromic Annihilator with Low-Lying Triplet

Development of excitation power-responsive anti-stokes emission wavelength switching and their energy saving induced by localized surface plasmon resonance

We designed an external stimulus-responsive anti-Stokes emission switching using dual-annihilator-based triplet-triplet annihilation upconversion systems. This system, which was constructed by incorporating a palladium porphyrin derivative as a sensitizer and 9,10-diphenylanthracene (DPA) and 9,10-bis(triisopropylsilyl)ethynylanthracene (TIPS) as annihilators into polymer thin films, produced TIPS- and DPA-based anti-Stokes emission under low and high excitation powers, respectively. The mechanism involves the following: under low excitation power, triplet energy transfer from triplet-excited PdOEP to DPA is induced, followed by relay to TIPS. This results in the generation of triplet-excited TIPS, and the subsequent triplet-triplet annihilation between them produces TIPS-based anti-Stokes emission. Conversely, under high excitation power, the high-density triplet-excited DPA, generated through triplet energy transfer from PdOEP, undergoes triplet-triplet annihilation among themselves, resulting in the generation of DPA-based anti-Stokes emission. Additionally, we achieved energy savings by reducing the required excitation power for switching through the utilization of plasmonic metal nanoparticles. The strong local electromagnetic fields associated with the localized surface plasmon resonance of metal nanoparticles enhance the photoexcitation efficiency of PdOEP, subsequently increasing the density of triplet-excited DPA. As a result, anti-Stokes emission switching becomes feasible at lower excitation powers.

Characterizations for the photothermal effect of Rhodamine 6G using white-light interferometry and windowed Fourier transform

Photothermal phenomenon is one of the natural responses in light-matter interactions in which the energy of the incident light is converted into heat, resulting in a temperature increase in the illuminated material. This effect has a direct influence on the refractive index of the material such that its change of spectral dependency with temperature can be exploited for different applications. However, it is also important to separate/identify the thermal effect from the optical/electronic resonance effect to expand potential applications of light-matter interactions. In this work, we demonstrate the use of a white-light interferometry approach combined with a windowed Fourier transform method and a consistency-checking peak-fitting method to obtain the refractive index of an Rh6G-ethanol dye solution with a sensitivity of about ∼10^-6 (RIU) for the visible range. Moreover, we also perform both static and dynamic measurements to study the photothermal effect of the Rh6G solution under external excitation. Importantly, we separate the optical and thermal effects due to the external excitation and obtain very good agreement with the experimental results by modeling the relative refractive index of the Rh6G solution with an expression consisting of spectrally a Fano-like resonance term and a linear dependent thermal term. We find that the response due to the optical effect is about ∼0.2 × 10^-3 of that due to the thermal effect in the low-light regime. Our approach to separating the optical and thermal effects could shed light on other fields for potential applications through precision measurements of the transmission phase or refractive index.

Micellar Ratiometric Fluorescent Blood pH Probe Based on Triplet-Sensitized Upconversion and Energy-Transfer Behaviors

The measurement of pH is greatly significant in monitoring physiological and biochemical states. In this work, a novel micellar ratiometric fluorescent probe featuring sophisticated energy-transfer (ET) behaviors with p-nitrophenol (PNP) as the energy acceptor and a triplet-triplet annihilation upconversion (TTA-UC) system as the energy donor was designed. The pH-induced molecular configuration of PNP determined the process for the transfer of energy from TTA-UC to PNP. The introduction of the TTA-UC system enabled probe excitation under a long wavelength and afforded a ratiometric signal for pH detection with excellent reliability over diverse interfering factors. This TTA-UC/ET pH probe demonstrated a high sensitivity to hydronium below nanomolar concentrations and an excellent anti-interference ability in serum samples, which provided a novel significant strategy for rapid and accurate detection of blood pH in vitro.

Future-Oriented Advanced Diarylethene Photoswitches: From Molecular Design to Spontaneous Assembly Systems

Diarylethene (DAE) photoswitch is a new and promising family of photochromic molecules and has shown superior performance as a smart trigger in stimulus-responsive materials. During the past few decades, the DAE family has achieved a leap from simple molecules to functional molecules and developed toward validity as a universal switching building block. In recent years, the introduction of DAE into an assembly system has been an attractive strategy that enables the photochromic behavior of the building blocks to be manifested at the level of the entire system, beyond the DAE unit itself. This assembly-based strategy will bring many unexpected results that promote the design and manufacture of a new generation of advanced materials. Here, recent advances in the design and fabrication of diarylethene as a trigger in materials science, chemistry, and biomedicine are reviewed.

A light-activatable photosensitizer for photodynamic therapy based on a diarylethene derivative

Herein, a light-activatable photosensitizer based on a diarylethene derivative, DAE-TPE, was developed for photodynamic therapy. Upon UV exposure, the "opened" form (OF) of DAE-TPE NPs was converted to the "closed" form (CF), and photosensitization was activated. The CF of DAE-TPE NPs exhibited sufficient photodynamic therapy effects upon HeLa cells.