Search

Donor-acceptor (D-A) conjugated polymers are of great interest as organic semiconductors, because they offer a rational tailoring of the electronic properties by modification of the donor and acceptor units. Nowadays, D-A polymers exhibit field-effect mobilities on the order of 10-2-100 cm2 V-1 s-1, while several examples showed a mobility over 10 cm2 V-1 s-1. The development of cyclopentadithiophene-benzothiadiazole (CDT-BTZ) copolymers one decade ago represents an important step toward high-performance organic semiconductors for field-effect transistors. The significant rise in field-effect mobility of CDT-BTZ in comparison to the existing D-A polymers at that time opened the door to a new research field with a large number of novel D-A systems. From this point, the device performance of CDT-BTZ was gradually improved by a systematic optimization of the synthesis and polymer structure as well as by an efficient solution processing into long-range ordered thin films. The key aspect was a comprehensive understanding of the relation between polymer structure and solid-state organization. Due to their fundamental role for the field of D-A polymers in general, this Account will for the first time explicitly focus on prototypical CDT-BTZ polymers, while other reviews provide an excellent general overview on D-A polymers. The first part of this Account discusses strategies for improving the charge carrier transport, focusing on chemical aspects. Improved synthesis as an essential stage toward high purity, and high molecular weight is a prerequisite for molecular order. The modification of substituents is a further crucial feature to tune the CDT-BTZ packing and self-assembly. Linear alkyl side chains facilitate intermolecular p-stacking interactions, while branched ones increase solubility and alter the polymer packing. Additional control over the supramolecular organization of CDT-BTZ polymers is introduced by alkenyl substituents via their cis-trans isomerization. The last discussed chemical concept is based on heteroatom variation within the CDT unit. The relationships found experimentally for CDT-BTZ between polymer chemical structure, solid-state organization, and charge carrier transport are explained by means of theoretical simulations. Besides the effects of molecular design, the second part of this Account discusses the processing conditions from solution. The film microstructure, defined as a mesoscopic domain organization, is critically affected by solution processing. Suitable processing techniques allow the formation of a long-range order and a uniaxial orientation of the CDT-BTZ chains, thus lowering the trapping density of grain boundaries for charge carriers. For instance, alignment of the CDT-BTZ polymer by dip-coating yields films with a pronounced structural and electrical anisotropy and favors a fast migration of charge carriers along the conjugated backbones in the deposition direction. By using film compression with the assistance of an ionic liquid, one even obtains CDT-BTZ films with a band-like transport and a transistor hole mobility of 10 cm2 V-1 s-1. This device performance is attributed to large domains in the compressed films being formed by CDT-BTZ with longer alkyl chains, which establish a fine balance between polymer interactions and growth kinetics during solvent evaporation. On the basis of the prototypical semiconductor CDT-BTZ, this Account provides general guidelines for achieving high-performance polymer transistors by taking into account the subtle balance of synthetic protocol, molecular design, and processing. [ABSTRACT FROM AUTHOR]

We present a feasible paradigm of developing original fluorescent probes for target biomolecules via combinatorial chemistry. In this developmental program, pyrimidine moieties were investigated and optimized as unique recognition units for thiols for the first time through a parallel synthesis in combination with a rapid screening process. This time-efficient and cost-saving process effectively facilitated the developmental progress and provided detailed structure-reactivity relationships. As a result, Res-Biot and Flu-Pht were identified as optimal fluorescent probes for biothiol and thiophenol, respectively. Their favorable characteristics and superior applicability have been well demonstrated in both chemical and biological contexts. In particular, Res-Biot enables the direct visualization of biothiol fluctuations during oxidative stress and cell apoptosis, indicating its suitability in elucidation of a specific pathophysiological process in both living cells and living animals. Meanwhile, Flu-Pht is competent to visualize thiophenols without the interference from endogenous biothiols in living cells. [ABSTRACT FROM AUTHOR]

A cyclometalated Pt(II) acetylide derivative bearing a bis(arylamine) donor (D) and a terpyridine (TPY) receptor (A) was successfully synthesized and characterized. This three-component D-π-A system displays an intense low-energy absorption band at λmax = 470 nm, resulting from overlapping the dπ(Pt) → π*(C^N^N) metal-to-ligand charge transfer and π(C≡C-Ar) → π*(C^N^N) ligand-to-ligand charge transfer transitions with the π(bis(arylamine)) → π*(C^N^N) intraligand charge transfer transition. Upon protonation of the bis(arylamine) donor, a strong emission from the phosphorescence Pt(II) complex unit is recovered at λmax = 580 nm. With introduction of the TPY receptor, this complex possesses quite high affinity for Zn2+ (Ka = 6.86 x 109 mol-2·dm6) to form the heterotrinuclear Pt-Zn-Pt complex in CH2Cl2 solution. Though this coordination effect is seriously inhibited by protons in acidic medium, the 2.4-fold luminescence intensity enhancement is obtained yet, strongly suggesting the presence of the intramolecular energy transfer process from the Zn(II)-TPY complex core to the phosphorescence Pt(II) complex units at two ends. The H+-triggered and Zn2+-enhanced luminescence can be reversibly switched on and off upon successive additions of H+ and OH-. Furthermore, this complex displays an unexpected Zn2+-selective luminescence enhancement effect in acidic solution. [ABSTRACT FROM AUTHOR]

A cyclometalated Pt(II) acetylide derivative bearing a bis(arylamine) donor (D) and a terpyridine (TPY) receptor (A) was successfully synthesized and characterized. This three-component D-π-A system displays an intense low-energy absorption band at λmax = 470 nm, resulting from overlapping the dπ(Pt) → π*(C^N^N) metal-to-ligand charge transfer and π(C=C-Ar) → π*(C^N^N) ligand-to-ligand charge transfer transitions with the π(bis(arylamine)) → π*(C^N^N) intraligand charge transfer transition. Upon protonation of the bis(arylamine) donor, a strong emission from the phosphorescence Pt(II) complex unit is recovered at λmax = 580 nm. With introduction of the TPY receptor, this complex possesses quite high affinity for Zn2+ (Ka = 6.86 × 109 mol-2dm6) to form the heterotrinuclear Pt-Zn-Pt complex in CH2Cl2 solution. Though this coordination effect is seriously inhibited by protons in acidic medium, the 2.4-fold luminescence intensity enhancement is obtained yet, strongly suggesting the presence of the intramolecular energy transfer process from the Zn(II)-TPY complex core to the phosphorescence Pt(II) complex units at two ends. The H+-triggered and Zn2+-enhanced luminescence can be reversibly switched on and off upon successive additions of H+ and OH-. Furthermore, this complex displays an unexpected Zn2+-selective luminescence enhancement effect in acidic solution. [ABSTRACT FROM AUTHOR]

A novel donor-acceptor polymer, PPhTQ, is synthesized by condensing a phenanthrene unit onto a thiadiazoloquinoxaline moiety. This polymer shows a broad absorption band from visible to near-infrared and a very low optical bandgap of 0.80 eV. A well-balanced ambipolar field-effect behavior is observed for PPhTQ, with mobilities of 0.09 cm² V-1 s-1 for holes and 0.06 cm² V-1 s-1 for electrons. A two-dimensional charge carrier transport in the film is determined by low-temperature resistance measurements, and an ordered molecular organization mainly in a face-on fashion is found by grazing incidence wide-angle X-ray scattering. More importantly, a PPhTQ thin film phototransistor exhibits an excellent device performance with a maximum photoresponsivity of 400 A/W. [ABSTRACT FROM AUTHOR]

Biomass burning covers open fires (forest and grassland fires, crop residue burning in fields, etc.) and biofuel combustion (crop residues and wood, etc., used as fuel). As a large agricultural country, China may produce large quantities of mercury emissions from biomass burning. A new mercury emission inventory in China is needed because previous studies reflected outdated biomass burning with coarse resolution. Moreover, these studies often adopted the emission factors (mass of emitted species per mass of biomass burned) measured in North America. In this study, the mercury emissions from biomass burning in China (excluding small islands in the South China Sea) were estimated, using recently measured mercury concentrations in various biomes in China as emission factors. Emissions from crop residues and fuelwood were estimated based on annual reports distributed by provincial government. Emissions from forest and grassland fires were calculated by combining moderate resolution imaging spectroradiometer (MODIS) burned area product with combustion efficiency (ratio of fuel consumption to total available fuels) considering fuel moisture. The average annual emission from biomass burning was 27 (range from 15.1 to 39.9) Mg/year. This inventory has high spatial resolution (1 km) and covers a long period (2000-2007), making it useful for air quality modeling. [ABSTRACT FROM AUTHOR]