5 research outputs found
Temperature dependent c-axis hole mobilities in rubrene single crystals determined by time-of-flight
Hole mobilities (μ) in rubrene single crystals (space group Cmca) along the crystallographic c-axis have been investigated as a function of temperature and applied electric field by the time-of-fight method. Measurements demonstrate an inverse power law dependence on temperature, namely,μ=μ0T−n with n = 1.8, from room temperature down to 180 K. At 296 K, the average value of μ was found to be 0.29 cm2/Vs increasing to an average value of 0.70 cm2/Vs at 180 K. Below 180 K a decrease in mobility is observed with further cooling. Overall, these results confirm the anisotropic nature of transport in rubrene crystals as well as the generality of the inverse power law temperature dependence that is observed for field effect mobility measurements in the a-b crystal plane
Synthesis and Charge-Transfer Dynamics in a Ferrocene-Containing Organoboryl aza-BODIPY Donor–Acceptor Triad with Boron as the Hub
A <i>N</i>,<i>N</i>′-bisÂ(ferroceneacetylene)Âboryl
complex of 3,3′-diphenylazadiisoindolylmethene was synthesized
by the reaction of an <i>N</i>,<i>N</i>′-difluoroboryl
complex of 3,3′-diphenylazadiisoindolylmethene and ferroceneacetylene
magnesium bromide. The novel diiron complex was characterized by a
variety of spectroscopic techniques, electrochemistry, and ultrafast
time-resolved methods. Spectroscopy and redox behavior was correlated
with the density functional theory (DFT) and time-dependent DFT calculations.
An unexpected degree of coupling between the two Fc ligands was observed.
Despite a lack of conjugation between the donor and acceptor, the
complex undergoes very rapid (τ = 1.7 ± 0.1 ps) photoinduced
intramolecular charge separation followed by subpicosecond charge
recombination to form a triplet state with a lifetime of 4.8 ±
0.1 μs
Nitrodibenzofuran: A One- and Two-Photon Sensitive Protecting Group That Is Superior to Brominated Hydroxycoumarin for Thiol Caging in Peptides
Nitrodibenzofuran: A One- and Two-Photon Sensitive Protecting Group That Is Superior to Brominated Hydroxycoumarin for Thiol Caging in Peptides
Photoremovable
protecting groups are important for a wide range
of applications in peptide chemistry. Using Fmoc-CysÂ(Bhc-MOM)-OH,
peptides containing a Bhc-protected cysteine residue can be easily
prepared. However, such protected thiols can undergo isomerization
to a dead-end product (a 4-methylcoumarin-3-yl thioether) upon photolysis.
To circumvent that photoisomerization problem, we explored the use
of nitrodibenzofuran (NDBF) for thiol protection by preparing cysteine-containing
peptides where the thiol is masked with an NDBF group. This was accomplished
by synthesizing Fmoc-CysÂ(NDBF)-OH and incorporating that residue into
peptides by standard solid-phase peptide synthesis procedures. Irradiation
with 365 nm light or two-photon excitation with 800 nm light resulted
in efficient deprotection. To probe biological utility, thiol group
uncaging was carried out using a peptide derived from the protein
K-Ras4B to yield a sequence that is a known substrate for protein
farnesyltransferase; irradiation of the NDBF-caged peptide in the
presence of the enzyme resulted in the formation of the farnesylated
product. Additionally, incubation of human ovarian carcinoma (SKOV3)
cells with an NDBF-caged version of a farnesylated peptide followed
by UV irradiation resulted in migration of the peptide from the cytosol/Golgi
to the plasma membrane due to enzymatic palmitoylation. Overall, the
high cleavage efficiency devoid of side reactions and significant
two-photon cross-section of NDBF render it superior to Bhc for thiol
group caging. This protecting group should be useful for a plethora
of applications ranging from the development of light-activatable
cysteine-containing peptides to the development of light-sensitive
biomaterials