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Fluorescent molecular rotors (FMRs) can act as viscosity sensors in various media including subcellular organelles and microfluidic channels. In FMRs, the rotation of rotators connected to a fluorescent π-conjugated bridge is suppressed by increasing environmental viscosity, resulting in increasing fluorescence (FL) intensity. In this minireview, we describe recently developed FMRs including push-pull type π-conjugated chromophores, meso-phenyl (borondipyrromethene) (BODIPY) derivatives, dioxaborine derivatives, cyanine derivatives, and porphyrin derivatives whose FL mechanism is viscosity-responsive. In addition, FMR design strategies for addressing various issues (e.g., obtaining high FL contrast, internal FL references, and FL intensity-contrast trade-off) and their biological and microfluidic applications are also discussed.

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Blue light has high photochemical energy and induces cell apoptosis in retinal pigment epithelial cells. Due to its phototoxicity, retinal hazard by blue light stimulation has been well demonstrated using high intensity light sources. However, it has not been studied whether blue light in the displays, emitting low intensity light, such as those used in today's smartphones, monitors, and TVs, also causes apoptosis in retinal pigment epithelial cells. We attempted to examine the blue light effect on human adult retinal epithelial cells using display devices with different blue light wavelength ranges, the peaks of which specifically appear at 449 nm, 458 nm, and 470 nm. When blue light was illuminated on A2E-loaded ARPE-19 cells using these displays, the display with a blue light peak at a shorter wavelength resulted in an increased production of reactive oxygen species (ROS). Moreover, the reduction of cell viability and induction of caspase-3/7 activity were more evident in A2E-loaded ARPE-19 cells after illumination by the display with a blue light peak at a shorter wavelength, especially at 449 nm. Additionally, white light was tested to examine the effect of blue light in a mixed color illumination with red and green lights. Consistent with the results obtained using only blue light, white light illuminated by display devices with a blue light peak at a shorter wavelength also triggered increased cell death and apoptosis compared to that illuminated by display devices with a blue light peak at longer wavelength. These results show that even at the low intensity utilized in the display devices, blue light can induce ROS production and apoptosis in retinal cells. Our results also suggest that the blue light hazard of display devices might be highly reduced if the display devices contain less short wavelength blue light.

We studied microcavity organic light-emitting devices with a microlens system. A microcavity for organic light-emitting devices (OLED) was fabricated by stacks of SiO(2) and SiN(x) layers and a metal cathode together with the microlens array. Electroluminescence of the devices showed that color variation under the viewing angle due to the microcavity is suppressed remarkably by microlens arrays, which makes the use of devices acceptable in many applications. It was also demonstrated that the external out-coupling factor of the devise increases by a factor of ~1.8 with wide viewing angles compared to conventional OLEDs.

Single crystal 3C-SiC epitaxial films are grown on Si(111) surfaces using tetramethylsilane by rapid thermal chemical vapor deposition. Strong blue/green photoluminescence (PL) was observed at room temperature from the free films of SiC prepared by etching the Si substrate. The main PL peak energy varies from 2.1 to 2.4 eV with full widths at half-maximum between 450 and 500 meV, depending on the growth condition, excitation wavelength and excitation light intensity. A weak peak at 3.0 eV also appeared. The infrared (IR) spectra of free films of SiC exhibit modes associated with CH and OH groups. We also compared PL characteristics of free films of SiC with those from porous SiC produced by anodization of SiC/Si to determine the origin of the PL. Porous SiC shows a PL peak centered at 1.9 eV, different from those in SiC. From the analysis of the IR spectra and scanning electron microscopic images, we tentatively suggest that the origin of the PL from free films of SiC might be associated with an OH group adsorbed on defects or some localized states as is the case for an amorphous SixC1−x alloy.

Sensitive imaging of inflammation with a background-free chemiluminescence (CL) signal has great potential as a clinically relevant way of early diagnosis for various inflammatory diseases. However, to date, its feasibility has been limitedly demonstrated in vivo with locally induced inflammation models by in situ injection of CL probes. To enable systemic disease targeting and imaging by intravenous administration of CL probes, hurdles need to be overcome such as weak CL emission, short glowing duration, or inability of long blood circulation. Here, we report a CL nanoprobe (BioNT) that surmounted such limitations to perform precise identification of inflammation by systemic self-delivery to the pathological tissues. This BioNT probe was engineered by physical nanointegration of multiple kinds of functional molecules into the ultrafine nanoreactor structure (∼15 nm in size) that combines solid-state fluorescence-induced enhanced peroxalate CL and built-in machinery to control the intraparticle kinetics of CL reaction. Upon intravenous injection into a normal mouse, BioNT showed facile blood circulation and generated a self-lighted strong CL torchlight throughout the whole body owing to the tiny colloidal structure with an antifouling surface as well as high CL sensitivity toward endogenous biological hydrogen peroxide (H2O2). In mouse models of local and systemic inflammations, blood-injected BioNT visualized precise locations of inflamed tissues with dual selectivity (selective probe accumulation and selective CL reaction with H2O2 overproduced by inflammation). Even a tumor model that demands a long blood circulation time for targeting (>3 h) could be accurately identified by persistent signaling from the kinetics-tailored BioNT with a 65-fold slowed CL decay rate. We also show that BioNT exhibits no apparent toxicity, thus holding potential for high-contrast diagnostic imaging.