2 research outputs found
Anion–Anion Interactions in the Crystal Packing of Functionalized Methanide Anions: An Experimental and Computational Study
Examination
of the crystal structures of (Me<sub>4</sub>N)Â(dcnm)
(<b>1</b>), (Me<sub>4</sub>N)Â(dcnom) (<b>2</b>), and (Me<sub>4</sub>N)Â(nbdm) (<b>3</b>) [dcnm = dicyanonitrosomethanide,
dcnom = dicyanonitromethanide, nbdm = nitroso-<i>N</i>,<i>N</i>-bisÂ(dicyanomethanide)] reveals the anions pack in an unusual
columnar array, with distances between the planar species suggestive
of π–π stacking. This columar packing motif is
not observed in the crystal structures of (Me<sub>4</sub>N)Â(ccnm)
(<b>4</b>) and (Me<sub>4</sub>N)Â(ccnom) (<b>6</b>) (ccnm
= carbamoylcyanonitrosomethanide, ccnom = carbamoylcyanonitromethanide),
in which hydrogen bonding between anions is the dominant supramolecular
interaction. Ab initio calculations performed at the HF and MP2 levels
of theory on ionic clusters of varying size further explored the nature
and strength of anionic interactions observed in crystal structures.
The first syntheses of the nbdm and ccnom anions are also reported
A Robust, High-Temperature Organic Semiconductor
We introduce a new pentacene-based
organic semiconductor, 5,6,7-trithiapentacene-13-one (TTPO). TTPO
is a small-molecule organic semiconductor that is simple to synthesize
and purify, readily crystallizes, melts in air from 386–388
°C without decomposition, and is indefinitely stable against
degradation in acid-free solution. TTPO has a high molar absorptivity,
optical and electrochemical HOMO–LUMO gaps of 1.90 and 1.71
eV, respectively, and can be thermally evaporated to produce highly
uniform thin films. Its cyclic voltammogram reveals one reversible
oxidation and two reversible reductions between +1.5 and −1.5
V. The crystal structure for TTPO has been solved and its unique parallel
displaced, and head-to-tail packing arrangement has been examined
and explained using high-level density functional theory. High-resolution
scanning tunneling microscopy (STM) was used to image individual TTPO
molecules upon assembly on a pristine Au(111) surface in ultrahigh
vacuum. STM images reveal that vapor-deposited TTPO molecules nucleate
in a unique stacked geometry with a small acute angle with respect
to Au(111) surface. Preliminary TTPO-based bilayer photovoltaic devices
show increases in short circuit current density upon heating from
25 to 80 °C with a concomitant 4–160-fold increase in
power conversion efficiencies. TTPO has the potential to be used in
thin-film electronic devices that require operation over a wide range
of temperatures such as thin-film transistors, sensors, switches,
and solar cells