Understanding and Countering Illumination-Sensitive Dark Current: Toward Organic Photodetectors with Reliable High Detectivity.

Continuously enhanced photoresponsivity and suppressed dark/noise current combinatorially lead to the recent development of high-detectivity organic photodetectors with broadband sensing competence. Despite the achievements, reliable photosensing enabled by organic photodetectors (OPDs) still faces challenges. Herein, we call for heed over a universal phenomenon of detrimental sensitivity of dark current to illumination history in high-performance inverted OPDs. The phenomenon, unfavorable to the attainment of high sensitivity and consistent figures-of-merit, is shown to arise from exposure of the commonly used electron transport layer in OPDs to high-energy photons and its consequent loss of charge selectivity via systematic studies. To solve this universal problem, "double" layer tin oxide as an alternative electron transport layer is demonstrated, which not only eliminates the inconsistency between the initial and after-illumination dark current characteristics but also preserves the low magnitude of dark current, good external quantum efficiency, and rapid transient response.

Phase Stability and Diffusion in Lateral Heterostructures of Methyl Ammonium Lead Halide Perovskites.

Mixed halide hybrid organic-inorganic perovskites have band gaps that span the visible spectrum making them candidates for optoelectronic devices. Transport of the halide atoms in methyl ammonium lead iodide (MAPbI3) and its alloys with bromine has been observed in both dark and under illumination. While halide transport upon application of electric fields has received much attention, less is known regarding bromide and iodide interdiffusion down concentration gradients. This work provides an upper bound on the bromide-iodide interdiffusion coefficient Di in thin films of MAPb(BrxI1-x)3 using a diffusion couples of lateral heterostructures. The upper bound of Di was extracted from changes in the interface profiles of the heterostructures upon exposure to heat. The stability of thoroughly heated interfacial profiles suggests that the miscibility gap extends to higher temperatures and to a higher fractional composition of bromine than predicted by theory. The results of this work provide guidance for compositions of thermally stable heterostructures of hybrid halide perovskites.

Transplantation effects of dental pulp-derived cells on peripheral nerve regeneration in crushed sciatic nerve injury.

The effects of transplanted human dental pulp-derived cells (DPCs) on peripheral nerve regeneration were studied in a rat model of sciatic nerve crush injury. In one group, DPCs were transplanted into the compression site (cell transplantation group); the control group underwent no transplantation (crushed group). Sciatic nerve regeneration was determined based on the recovery of motor function and histological and immunohistochemical analyses. The cell transplantation group showed improved motor function compared with the crushed group using the CatWalk XT system, which corresponded to a higher ratio of tibialis to anterior muscle weight 14 days after surgery. Histological analysis revealed a smaller interspace area and few vacuoles in the sciatic nerve after cell transplantation compared with the crushed group. The myelin sheath was visualized with Luxol Fast Blue (LFB) staining and anti-myelin basic protein (anti-MBP) antibody labeling; the percentages of LFB- and MBP-positive areas were higher in the cell transplantation group than in the crushed group. Human mitochondria-positive cells were also identified in the sciatic nerve at the transplantation site 14 days after surgery. Taken together, the observed correlation between morphological findings and functional outcomes following DPC transplantation indicates that DPCs promote peripheral nerve regeneration in rats.

A Case of Bisphosphonate-Related Osteonecrosis of the Jaw in a Patient with Subpontic Osseous Hyperplasia.

Subpontic osseous hyperplasia (SOH) is a growth of bone occurring on the edentulous ridge beneath the pontics of fixed partial dentures (FPDs). This report describes a case of bisphosphonate- (BP-) related osteonecrosis of the jaw (BRONJ) in a SOH patient followed by deciduation of the bony lesion. A 73-year-old woman visited a dental clinic after experiencing pain and swelling beneath the pontics of a FPD that had been inserted 15 years ago. The pontics were removed, but the symptoms persisted and she was referred to our hospital. There was an osseous bulge and gum swelling around the edentulous ridge of teeth 18 and 19, as well as bone exposure. As she had been taking an oral BP for 6 years, we diagnosed this case as stage 2 BRONJ. Following BP withdrawal, the bony lesion detached from the mandible. The tissue was diagnosed as sequestrum based on the histopathological findings. Two months after deciduation, epithelialization over the area of exposed bone was achieved and no recurrence has been observed.

Trophic Effects of Dental Pulp Stem Cells on Schwann Cells in Peripheral Nerve Regeneration.

Recently, mesenchymal stem cells have demonstrated a potential for neurotrophy and neurodifferentiation. We have recently isolated mobilized dental pulp stem cells (MDPSCs) using granulocyte-colony stimulating factor (G-CSF) gradient, which has high neurotrophic/angiogenic potential. The aim of this study is to investigate the effects of MDPSC transplantation on peripheral nerve regeneration. Effects of MDPSC transplantation were examined in a rat sciatic nerve defect model and compared with autografts and control conduits containing collagen scaffold. Effects of conditioned medium of MDPSCs were also evaluated in vitro. Transplantation of MDPSCs in the defect demonstrated regeneration of myelinated fibers, whose axons were significantly higher in density compared with those in autografts and control conduits only. Enhanced revascularization was also observed in the MDPSC transplants. The MDPSCs did not directly differentiate into Schwann cell phenotype; localization of these cells near Schwann cells induced several neurotrophic factors. Immunofluorescence labeling demonstrated reduced apoptosis and increased proliferation in resident Schwann cells in the MDPSC transplant compared with control conduits. These trophic effects of MDPSCs on proliferation, migration, and antiapoptosis in Schwann cells were further elucidated in vitro. The results demonstrate that MDPSCs promote axon regeneration through trophic functions, acting on Schwann cells, and promoting angiogenesis.

Suppression of HOMO-LUMO transition in a twist form of oligo(phenyleneethynylene) clamped by a right-handed helical peptide.

A donor-π-acceptor (D-π-A) system of oligo(phenyleneethynylene) (OPE) was twisted by clamping both ends of the OPE with a right-handed helical peptide (SSA8=OPE). The induced twist in OPE was in a right-handed way. SSA8=OPE showed a weaker HOMO-LUMO band in the absorption spectrum than that of a reference compound AcOPE without the helix bridge. The fluorescence quantum yield of SSA8=OPE was extremely low (0.0045-0.0165), which was in contrast to AcOPE with a moderate quantum yield of 0.355. The fluorescence life times of SSA8=OPE and AcOPE were nearly the same. Time-dependent density functional theory calculations (b3lyp/6-31G(d,p) level) on a twisted conformation of the D-π-A system qualitatively reproduced CD spectra and UV spectra of a weak oscillator strength of the HOMO-LUMO transition. Upon twisting the D-π-A system, the oscillator strength of the HOMO-LUMO transition is thus reduced.

Ultra-long-range electron transfer through a self-assembled monolayer on gold composed of 120-Å-long α-helices.

Electron transfer through α-helices has attracted much attention from the viewpoints of their contributions to efficient long-range electron transfer occurring in biological systems and their utility as molecular-electronics elements. In this study, we synthesized a long 80mer helical peptide carrying a redox-active ferrocene unit at the terminal and immobilized the helical peptide on a gold surface. The molecular length is calculated to be 134 Å, in which the helix accounts for 120 Å. The preparation conditions of the self-assembled monolayers were intentionally changed to obtain monolayers with different physical states to study the correlation between molecular motions and electron transfer. Ellipsometry and infrared spectroscopy showed that the helical peptide forms a self-assembled monolayer with vertical orientation. Electrochemical measurements revealed that an electron is transferred from the ferrocene unit to gold through the monolayer composed of this long helical peptide, and the experimental data are well explained by theoretical results calculated under the assumption that electron transfer occurs by a unique hopping mechanism with the amide groups as hopping sites. Furthermore, we have observed a unique dependence of electron transfer on the monolayer packing, suggesting the importance of structural fluctuations of peptides on the electron transfer controlled by the hopping mechanism.

Dipole effects on molecular and electronic structures in a novel conjugate of oligo(phenyleneethynylene) and helical peptide.

A novel conjugate of a helical nonapeptide and an oligo(phenyleneethynylene) (OPE) having a nitro group at a molecular terminal was synthesized. Both components have a dipole. The peptide has a disulfide group at the N-terminal for immobilization on gold. In order to investigate the electric field effect of the helical peptide dipole on the OPE and molecular structure by the dipole-dipole interaction between the two components, the electronic structure of the OPE was spectroscopically studied in solution, the self-assembled monolayer on gold, and Langmuir-Blodgett (LB) layers on a fused quartz surface. The absorption maximum (lambda(max)) of the OPE component in chloroform is red-shifted by 4 nm from the reference OPE derivative without the helical peptide component. The red shifts of the OPE component are also observed in the LB monolayer and bilayer compared with that of the self-assembled monolayer. The observed dipole effect of the peptide on the OPE electronic structure was quantitatively discussed with ab initio calculations. Antiparallel orientation on the dipole directions of the peptide and the OPE components is considered to explain the red shifts via the dipole effect on the electronic structure of the OPE.

Chirally twisted oligo(phenyleneethynylene) by cyclization with alpha-helical peptide.

A novel cyclic conjugate of a helical decapeptide and oligo(phenyleneethynylene) (OPE), C-OPE10, was synthesized. The conformation and the optical properties of the cyclic conjugate were studied by circular dichroism (CD), absorption, and emission spectroscopies. In the cyclic conjugate, the rotational motion around the molecular axis of the OPE moiety was hindered to take a chirally twisted conformation, which is a distorted form from the coplanar conjugated structure, as revealed by observation of an induced negative Cotton effect of the OPE moiety. Molecular simulation using time dependant-density functional theory indicated a right-handed twist conformation of the OPE moiety for the negative Cotton effect. This conjugate therefore provides a new way to obtain a pi-conjugated compound having main-chain chirality. The optical properties of the OPE moiety taking the twist conformation in the cyclic conjugate are also discussed in depth.