Universal relation between the conditional auto-correlation function and the cross-correlation function of biphotons.

We systematically studied the relation between the conditional auto-correlation function (CACF) and cross-correlation function (CCF) of biphotons or pairs of single photons. The biphotons were generated from a heated atomic vapor via the spontaneous four-wave mixing (SFWM) process. In practical usage, one single photon of a pair is utilized as the heralding photon, and another is employed as the heralded photon. Motivated by the data of CACF of the heralded photons versus CCF, we proposed a universal formula to predict the CACF. The derived formula was based on general theory and is also valid for the biphoton generation process of spontaneous parametric down-conversion (SPDC). With the formula, we utilized the experimentally determined parameters to predict CACFs, which can well agree with the measured CACFs. The proposed formula enables one to quantitatively know the CACF of heralded single photons without the measurement of Hanbury-Brown-Twiss-type three-fold coincidence count. This study provides a better understanding of biphoton generation using the SFWM or SPDC process. Our work demonstrates a valuable tool for analyzing a vital property of how the heralded photons are close to Fock-state single photons.

Analysis of hybrid plasmon-phonon-polariton modes in hBN/graphene/hBN stacks for mid-infrared waveguiding.

Guiding mid-infrared (mid-IR) signals provide wide-ranging applications including chemical sensing, thermal imaging, and optical waveguiding. To manipulate mid-IR signals on photonic chips, it is critical to build a waveguide that provides both sub-diffraction field confinement and low loss. We present a mid-IR waveguide made up of a multilayer graphene/hexagonal boron nitride (hBN) stacking (MLGhS) and a high-refractive index nanowire. The guided mode of the proposed waveguide structure is formed by coupling the fundamental volume plasmon polariton with the fundamental hyperbolic phonon polariton in hBN, and is then modulated by a high-index nanowire. Interestingly, we found that the effective index, propagation length, and mode area of the guided mode vary as the dependences of N-1, N, and N3/2, where N is the number of graphene layers. In addition, an anomalous result, which reveals Lp and Am monotonously decrease as Fermi energy increases that is not observed in conventional graphene plasmon waveguides, occurs in the present structure. The modal properties are analyzed by altering geometry effects and material parameters, and by crossing the upper Reststrahlen band of hBN from the wavevector k = 1,300 to 1,500 cm-1. Furthermore, crosstalk between adjacent waveguides are investigated to assess the degree of integration. The proposed idea not only provides a potential approach for designing tunable and large-area photonic integrated circuits, but it also has the potential to be extended to other 2D materials such as silicone, germanene, and stanene.

Supramolecular Chemistry of Anionic Dimers, Trimers, Tetramers and Clusters.

Two or more anions constrained in close proximity within a single pocket are found in a number of natural systems but a less common motif in artificial systems. This review summarizes work on anion receptors capable of stabilizing anionic dimers, trimers, tetramers and clusters in a well-defined fashion. These systems may provide insights into the fundamental chemistry of anion-anion interactions and provide a guide for understanding in greater detail a number of biological and environmental processes, as well as key tenants of relevance to supramolecular chemistry, extraction, transport, crystal engineering, and the like. The primary goal of this review is to provide a general introduction into multi-anion recognition chemistry for the benefit of supramolecular and non-supramolecular chemists alike.

Hetero Cu(III)-Pd(II) Complex of a Dibenzo[g,p]chrysene-Fused Bis-dicarbacorrole with Stable Organic Radical Character.

Bis-dicarbacorrole (bis-H3) with two adj-CCNN subunits was synthesized by incorporating a dibenzo[g,p]chrysene moiety into the macrocyclic structure. The two trianionic cores in bis-H3 can stabilize two Cu(III) ions (bis-Cu) or concurrently a Cu(III) cation and a Pd(II) ion in the form of a hetero bis-metal complex (mix-Cu/Pd). As prepared, mix-Cu/Pd displays organic π radical character, as confirmed by various techniques, including electron paramagnetic resonance spectroscopy, cyclic voltammetry, femtosecond transient absorption measurements, and DFT calculations. Radical formation is ascribed to one-electron transfer from the dicarbacorrole backbone to the Pd center allowing the d8 Pd(II) center to be accommodated in a square planner coordination geometry. Nucleus-independent chemical shift and anisotropy of the induced current density calculations provide support for the conclusion that bis-H3 and bis-Cu both display antiaromatic character and contain two formally 16 π-electron dicarbacorrole subunits. On this basis, we suggest that mix-Cu/Pd is best considered as containing a fused 15 π-electron nonaromatic radical subunit and a 16 π-electron antiaromatic subunit. The spectroscopic observations are consistent with these assignments.

Amyloid-ß Deposits Target Efficient Near-Infrared Fluorescent Probes: Synthesis, in Vitro Evaluation, and in Vivo Imaging.

The formation of extracellular amyloid-ß (Aß) plaques is a common molecular change that underlies several debilitating human conditions, including Alzheimer's disease (AD); however, the existing near-infrared (NIR) fluorescent probes for the in vivo detection of Aß plaques are limited by undesirable fluorescent properties and poor brain kinetics. In this work, we designed, synthesized, and evaluated a new family of efficient NIR probes that target Aß plaques by incorporating hydroxyethyl groups into the ligand structure. Among these probes, DANIR 8c showed excellent fluorescent properties with an emission maximum above 670 nm upon binding to Aß aggregates and also displayed a high sensitivity (a 629-fold increase in fluorescence intensity) and affinity (Kd = 14.5 nM). Because of the improved hydrophilicity that was induced by hydroxyls, 8c displayed increased initial brain uptake and a fast washout from the brain, as well as an acceptable biostability in the brain. In vivo NIR fluorescent imaging revealed that 8c could efficiently distinguish between AD transgenic model mice and normal controls. Overall, 8c is an efficient and veritable NIR fluorescent probe for the in vivo detection of Aß plaques in the brain.

Highly Sensitive Near-Infrared Fluorophores for in Vivo Detection of Amyloid-ß Plaques in Alzheimer's Disease.

Alzheimer's disease (AD) is pathologically characterized by the accumulation of ß-amyloid (Aß) deposits in the parenchymal and cortical brain. In this work, we designed, synthesized, and evaluated a series of near-infrared (NIR) probes with electron donor-acceptor end groups interacting through a π-conjugated system for the detection of Aß deposits in the brain. Among these probes, 3b and 3c had excellent fluorescent properties (emission maxima > 650 nm and high quantum yields) and displayed high sensitivity and high affinities to Aß aggregates (3b, Kd = 8.8 nM; 3c, Kd = 1.9 nM). Both 3b and 3c could readily penetrate the blood-brain barrier with high initial brain uptake and fast to moderate washout from the brain. In vivo NIR imaging revealed that 3b and 3c could efficiently differentiate transgenic and wild-type mice. In summary, our research provides new hints for developing smarter and more activatable NIR probes targeting Aß.

Compounds for imaging amyloid-ß deposits in an Alzheimer's brain: a patent review.

INTRODUCTION: ß-amyloid (Aß) plaques in the brain are regarded as a hallmark of Alzheimer's disease (AD), and the imaging of Aß is a critical step for early diagnosis. Extensive research has been done to develop probes for targeting Aß with available imaging modalities. AREAS COVERED: In this review, the authors give an overview of published patents and papers about the discovery and development of compounds possessing potential utilization in imaging Aß for the diagnosis of AD. SciFinder is the main electronic database for patent study in this review. EXPERT OPINION: Despite achievements in Aß imaging, there is still a need to develop innovative compounds with selectivity and high affinity to Aß. Positron emission tomography imaging agents will still be the trend in the field in the short term. Due to the low costs for single-photon emission computed tomography (SPECT) and the excellent nuclear properties of (99m)Tc, substantial research should be conducted on the development of the probes for SPECT. Refining the current imaging techniques and in the meantime developing new efficient imaging multimodality and compounds would be a promising approach to imaging Aß.

Evaluation of molecules based on the electron donor-acceptor architecture as near-infrared ß-amyloidal-targeting probes.

A novel class of near-infrared molecules based on the donor-acceptor architecture were synthesized and evaluated as Aß imaging probes. In vivo imaging studies suggested that MCAAD-3 could penetrate the blood-brain barrier and label Aß plaques in the brains of transgenic mice. Computational studies could reproduce the experimental trends well.