Regioregular pyridal[2,1,3]thiadiazole π-conjugated copolymers

π-Conjugated, narrow band gap copolymers containing pyridal[2,1,3]thiadiazole (PT) were synthesized via starting materials that prevent random incorporation of the PT heterocycles relative to the backbone vector. Two regioregular structures could be obtained: in one the PTs are oriented in the same direction, and in the other the orientation of the PTs alternates every other repeat unit. Compared to their regiorandom counterparts, the regioregular polymers exhibit a 2 orders of magnitude increase of the hole mobilites, from 0.005 to 0.6 cm(2) V(-1) s(-1), as determined by field-effect transistor measurements.     

Heteroanalogues of PCBM: N‐Bridged Imino‐PCBMs for Organic Field‐Effect Transistors

Crossing the bridge : Two isomeric iminofullerenes, [5,6]‐open azafulleroid 1 and [6,6]‐closed aziridinofullerene 2 , were prepared by cycloaddition of an organic azide to C₆₀. These “azalogues” enable the study of the effects of the bridging atom in a fullerene cage, that is, C₆₀‐like (5,6‐open) versus PCBM‐like (6,6‐closed), as a function of their π systems (PCBM=[6,6]‐phenyl‐C₆₁‐butyric acid methyl ester).

     

Amorphous iridium complexes for electrophosphorescent light emitting devices

Iridium complexes with fluorene-modified phenylpyridine ligands are resistant to crystallization and can be used in the fabrication of single layer light emitting diodes.     

Low temperature specific heat of (TTF) (TCNQ)

Low temperature specific heat measurements on (TTF) (TCNQ) are reported. The Debye temperature is 89.5 K. No term linear in temperature is observed, and comparison with other data indicates the low temperature phase is that of a small band gap non-magnetic semiconductor.     

Specific heats of pure and doped polyacetylene

The temperature dependences (0.8 K ? T < 7 K) of the specific heats of pure polyacetylene (both $\text{cis}$ and $\text{trans}$ isomers) and heavily doped metallic [CH(AsF₅)_0.12]_X are reported. Results for undoped $\text{cis}$-(CH)_X indicate behavior typical of crystalline polymers, whereas isomerization to the $\text{trans}$-form leads to a small term linear in temperature signifying increased disorder. Comparison of the data from $\text{cis}$ and $\text{trans}$ starting material indicates that isomerization is induced during doping. The increased coefficient of the linear term in the metallic polymer is discussed in terms of two contributions; an electronic term expected for a metal, and the increased effect of disorder in the doped polymer.     

Photoconductivity in polyacetylene

The results of steady state photoconductivity experiments on cis- and trans-(CH)_x are interpreted in terms of charged solitons, photogenerated either directly (threshold hv = 4Δ/π) or indirectly through coupling of the lattice to electron-hole pair excitations (hv ? 2Δ). The transient photocurrent, after laser pulse excitation, decays as a power law, I(t) ? t^?0.6, suggesting dispersive transport of the photogenerated carriers.     

Superconductivity in Hg3-δAsF6: Absence of surface mercury

Low temperature resistance and X-ray fluorescence measurements indicate that the anisotropic superconductivity of Hg_3-δAsF₆ does $\text{not}$ arise from a surface film of extruded mercury. Meissner effect data demomstrate that the superconductivity goes to complete flux exclusion below 0.43 K.     

Non-linear transport in tetrathiofulvalene-tetracyanoquinodimethane: An electron spin resonance study

We describe an ESR study of pure and irradiated TTF-TCNQ in the low temperature range (1.2 K–4.2 K) where nonlinear transport has been observed. We find no evidence of an activated term in the susceptibility; our results yield an upper limit of about 10 ppm for nonmagnetic impurities with a spin-$\text{1}\text{2}$ excited state. Since in pure samples, the activated susceptibility term is not present whereas the transport nonlinearity is clearly seen, we conclude that the latter cannot be attributed to hot electron effects. The susceptibility and dc bias studies are consistent with a nonmagnetic soliton picture. We have monitored the spin resonance in the presence of a dc bias current. Using the Curie law as an internal thermometer we are able to set an upper limit on sample heating of 0.1 K at the highest dc levels used.