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>′-bis­(ferroceneacetylene)­boryl 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

Photoremovable protecting groups are important for a wide range of applications in peptide chemistry. Using Fmoc-Cys­(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-Cys­(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