Qingdong Zheng

Multiphoton Absorbing Materials: Molecular Designs, Characterizations, and Applications

4. Survey of Novel Multiphoton Active Materials 1257 4.1. Multiphoton Absorbing Systems 1257 4.2. Organic Molecules 1257 4.3. Organic Liquids and Liquid Crystals 1259 4.4. Conjugated Polymers 1259 4.4.1. Polydiacetylenes 1261 4.4.2. Polyphenylenevinylenes (PPVs) 1261 4.4.3. Polythiophenes 1263 4.4.4. Other Conjugated Polymers 1265 4.4.5. Dendrimers 1265 4.4.6. Hyperbranched Polymers 1267 4.5. Fullerenes 1267 4.6. Coordination and Organometallic Compounds 1271 4.6.1. Metal Dithiolenes 1271 4.6.2. Pyridine-Based Multidentate Ligands 1272 4.6.3. Other Transition-Metal Complexes 1273 4.6.4. Lanthanide Complexes 1275 4.6.5. Ferrocene Derivatives 1275 4.6.6. Alkynylruthenium Complexes 1279 4.6.7. Platinum Acetylides 1279 4.7. Porphyrins and Metallophophyrins 1279 4.8. Nanoparticles 1281 4.9. Biomolecules and Derivatives 1282 5. Nonlinear Optical Characterizations of Multiphoton Active Materials 1282

Applications of ZnO in organic and hybrid solar cells

As an n-type inorganic semiconductor, ZnO has been widely used in organic solar cells (OSCs) and hybrid solar cells (HSCs) due to its salient characteristics such as low cost, easy synthesis, non-toxicity, high stability, and good optoelectronic properties. This article reviews the applications of ZnO in solar cells, including ZnO/organic HSCs, and OSCs with ZnO acting as electrode buffer layers or transparent electrodes. For ZnO/organic HSCs, ZnO serves as the electron acceptor material, while organic semiconductors act as electron donor materials. For the buffer layers or electrode applications, ZnO is used as an electron collection and hole blocking material where its structure plays an important role in the determination of the device performance (e.g., power conversion efficiency, lifetime, stability, etc.). Special emphasis goes to the device performance of OSCs and HSCs, which depends not only on the active materials and the device configurations, but also on the structural characteristics of the ZnO buffer layer. Finally, we briefly give an analysis on the opportunities and challenges for this promising semiconductor in OSCs and HSCs.

LADDER-TYPE OLIGO-P-PHENYLENE-CONTAINING COPOLYMERS WITH HIGH OPEN-CIRCUIT VOLTAGES AND AMBIENT PHOTOVOLTAIC ACTIVITY

Four ladder-type oligo-p-phenylene containing donor-acceptor copolymers were designed, synthesized, and characterized. The ladder-type oligo-p-phenylene was used as an electron donor unit in these copolymers to provide a deeper highest occupied molecular orbital (HOMO) level for obtaining polymer solar cells with a higher open-circuit voltage, while 4,7-dithien-2-yl-2,1,3-benzothiadiazole or 5,8-dithien-2-yl-2,3-diphenylquinoxaline was chosen as an electron acceptor unit to tune the electronic band gaps of the polymers for a better light harvesting ability. These copolymers exhibit field-effect mobilities as high as 0.011 cm(2)/(V s). Compared to fluorene containing copolymers with the same acceptor unit, these ladder-type oligo-p-phenylene containing copolymers have enhanced and bathochromically shifted absorption bands and much better solubility in organic solvents. Photovoltaic applications of these polymers as light-harvesting and hole-conducting materials are investigated in conjunction with [6,6]-phenyl-C61-butyric acid methyl ester (PC(61)BM) or [6,6]-phenyl-C71-butyric acid methyl ester (PC(71)BM). Without extensive optimization work, a power conversion efficiency (PCE) of 3.7% and a high open-circuit voltage of 1.06 V are obtained under simulated solar light AM 1.5 G (100 mW/cm(2)) from a solar cell with an active layer containing 20 wt % ladder-type tetra-p-phenylene containing copolymer (P3FTBT6) and 80 wt % PC(61)BM. Moreover, a high PCE of 4.5% was also achieved from a solar cell with an active layer containing 20 wt % P3FTBT6 and 80 wt % PC(71)BM.

Conformationally restricted dipyrromethene boron difluoride (BODIPY) dyes: highly fluorescent, multicolored probes for cellular imaging.

Novel fluorescent, conformationally restricted dipyrromethene boron difluoride (BODIPY) dyes have been prepared by introducing a naphthalenyl group at the meso position of the BODIPY core. These BODIPY dyes exhibit increased fluorescence quantum yields compared with dyes that have a meso-position phenyl group with internal rotation. The absorption and emission wavelengths of such conformationally restricted BODIPY dyes can be easily tuned to the near-IR range by derivatization through a condensation reaction with benzaldehyde derivatives. The two-photon absorption properties of these BODIPY dyes were also investigated and the results show that they exhibit increased two-photon excited fluorescence compared to analogue dyes that contain a phenyl group. The one- and two-photon fluorescence imaging of living cells by using selected BODIPY dyes has been successfully demonstrated.

Multi-photon excitation properties of CdSe quantum dots solutions and optical limiting behavior in infrared range.

Multi-photon absorption and excitation properties of CdSe quantum dots in hexane with different dot-sizes have been investigated. The two- and three-photon absorption (2PA and 3PA) coefficients were measured by using ~160-fs laser pulses at wavelengths of ~775-nm and ~1300-nm, respectively. The dependence of one-, two- and three-photon induced fluorescence spectra as well as their double-exponential decay on the dot-sizes was studied. Based on the fluorescence emission spectra and temporal decay constants for a given sample solution excited by one-, two-and three-photon absorption, it can be concluded that the transition pathways for fluorescence emission and decay under one-, two- and three-photon excitation are nearly identical. The optical power limiting capabilities based on 2PA and 3PA mechanisms are demonstrated separately. In addition, a saturation behavior of 3PA at ~1300 nm was observed.

Interfacial Materials for Organic Solar Cells: Recent Advances and Perspectives.

Organic solar cells (OSCs) have shown great promise as low‐cost photovoltaic devices for solar energy conversion over the past decade. Interfacial engineering provides a powerful strategy to enhance efficiency and stability of OSCs. With the rapid advances of interface layer materials and active layer materials, power conversion efficiencies (PCEs) of both single‐junction and tandem OSCs have exceeded a landmark value of 10%. This review summarizes the latest advances in interfacial layers for single‐junction and tandem OSCs. Electron or hole transporting materials, including metal oxides, polymers/small‐molecules, metals and metal salts/complexes, carbon‐based materials, organic‐inorganic hybrids/composites, and other emerging materials, are systemically presented as cathode and anode interface layers for high performance OSCs. Meanwhile, incorporating these electron‐transporting and hole‐transporting layer materials as building blocks, a variety of interconnecting layers for conventional or inverted tandem OSCs are comprehensively discussed, along with their functions to bridge the difference between adjacent subcells. By analyzing the structure–property relationships of various interfacial materials, the important design rules for such materials towards high efficiency and stable OSCs are highlighted. Finally, we present a brief summary as well as some perspectives to help researchers understand the current challenges and opportunities in this emerging area of research.

Pyromellitic Diimides: Minimal Cores for High Mobility n-Channel Transistor Semiconductors

Three pyromellitic diimides were synthesized in high yields by one conventional reaction between pyromellitic dianhydride and various amines. The films made from these pyromellitic diimides derivatives exhibit a mobility up to 0.079 cm2/(V.s). In addition, the on/off ratios of n-channel devices are as high as 1 000 000.

Degenerate two-/three-photon absorption and optical power-limiting properties in femtosecond regime of a multi-branched chromophore

The degenerate two- and three-photon absorption properties of a multi-branched chromophore were investigated in the femtosecond regime utilizing white-light continuum and nonlinear transmission techniques. The experimental results show that the studied multi-branched structure exhibits relatively strong and broad two- and three-photon absorption bands in the near infra-red (IR) region. It is demonstrated that a highly conjugated molecular structure based on a symmetrically substituted skeleton would possess promoted molecular nonlinear absorptivities within the studied spectral region. Both two- and three-photon absorption-based optical power-limiting properties in the femtosecond time domain of this model compound were also characterized. The results indicate that a multi-chromophoric structure with expanded π-conjugation could be an effective multi-photon absorber and might be used as a single-component material system for quick-responsive and broadband optical-suppressing related applications, especially when under ultrashort laser pulses.

Silica-based nanoparticle uptake and cellular response by primary microglia.

Background Silica nanoparticles (SiNPs) are being formulated for cellular imaging and for nonviral gene delivery in the central nervous system (CNS), but it is unclear what potential effects SiNPs can elicit once they enter the CNS. As the resident macrophages of the CNS, microglia are the cells most likely to respond to SiNP entry into the brain. Upon activation, they are capable of undergoing morphological and functional changes. Objective We examined the effects of SiNP exposure using primary rat microglia. Methods We observed microglial uptake of SiNPs using transmission electron and fluorescence confocal microscopy. Microglial functions, including phagocytosis, generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS), expression of proinflammatory genes, and cytokine release, were measured after SiNP exposure at different concentrations. Results Microglia are capable of avidly taking up SiNPs at all concentrations tested. These same concentrations did not elicit cytotoxicity or a change in phagocytic activity. SiNPs did increase the productions of both intracellular ROS and RNS. We also observed a significant decrease in tumor necrosis factor-α gene expression at all concentrations tested and a significant increase in COX-2 (cyclooxygenase-2) gene expression at the highest concentration of SiNPs. Analysis of cytokine release showed a detectable level of interleukin-1β. Conclusions This is the first study demonstrating the in vitro effects of SiNPs in primary microglia. Our findings suggest that very low levels of SiNPs are capable of altering microglial function. Increased ROS and RNS production, changes in proinflammatory genes, and cytokine release may not only adversely affect microglial function but also affect surrounding neurons.

Two- and three-photon absorption and frequency upconverted emission of silicon quantum dots.

In this communication, we present the experimental results of two- and three-photon excitation studies on silicon quantum dots (QDs) in chloroform (as well as in water) by using femtosecond laser pulses with wavelengths of 778 and 1,335 nm and a pulse duration approximately 160 fs. The photoluminescence spectral distributions are nearly the same upon one-, two-, and three-photon excitation. With one- and two-photon excitation, the temporal relaxation measurements of photoluminescence emission manifest the same multiexponential decay behavior in the time range from 0.05 ns to 15 micros, characterized by three successive decay constants: 0.75 ns, 300 ns, and 5 micros, respectively. Finally, the two-photon absorption spectrum in the spectral range of 650-900 nm and the three-photon absorption spectrum in the spectral range of 1,150-1,400 nm have been measured.