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Open AccessArticle

Mesomorphic Behavior in Silver(I) N-(4-Pyridyl) Benzamide with Aromatic π–π Stacking Counterions

1
Department of Chemistry, University of Texas at El Paso, El Paso, TX 79968, USA
2
Department of Chemistry & Biochemistry, University of California Santa Barbara, Santa Barbara, CA 93106-9510, USA
3
Department of Chemistry, University of Colorado, Denver, CO 80217-3364, USA
4
Department of Physics, University of Texas at El Paso, El Paso, TX 79968, USA
5
Department of Chemistry, University of Utah, Salt Lake City, UT 84112, USA
*
Author to whom correspondence should be addressed.
Materials 2018, 11(9), 1666; https://doi.org/10.3390/ma11091666
Received: 20 June 2018 / Revised: 3 August 2018 / Accepted: 3 September 2018 / Published: 9 September 2018
Organic semiconductor materials composed of π–π stacking aromatic compounds have been under intense investigation for their potential uses in flexible electronics and other advanced technologies. Herein we report a new family of seven π–π stacking compounds of silver(I) bis-N-(4-pyridyl) benzamide with varying counterions, namely [Ag(NPBA)2]X, where NPBA is N-(4-pyridyl) benzamine, X = NO3 (1), ClO4 (2), CF3SO3 (3), PF6 (4), BF4 (5), CH3PhSO3 (6), and PhSO3 (7), which form extended π−π stacking networks in one-dimensional (1D), 2D and 3D directions in the crystalline solid-state via the phenyl moiety, with average inter-ring distances of 3.823 Å. Interestingly, the counterions that contain π–π stacking-capable groups, such as in 6 and 7, can induce the formation of mesomorphic phases at 130 °C in dimethylformamide (DMF), and can generate highly branched networks at the mesoscale. Atomic force microscopy studies showed that 2D interconnected fibers form right after nucleation, and they extend from ~30 nm in diameter grow to reach the micron scale, which suggests that it may be possible to stop the process in order to obtain nanofibers. Differential scanning calorimetry studies showed no remarkable thermal behavior in the complexes in the solid state, which suggests that the mesomorphic phases originate from the mechanisms that occur in the DMF solution at high temperatures. An all-electron level simulation of the band gaps using NRLMOL (Naval Research Laboratory Molecular Research Library) on the crystals gave 3.25 eV for (1), 3.68 eV for (2), 1.48 eV for (3), 5.08 eV for (4), 1.53 eV for (5), and 3.55 eV for (6). Mesomorphic behavior in materials containing π–π stacking aromatic interactions that also exhibit low-band gap properties may pave the way to a new generation of highly branched organic semiconductors. View Full-Text
Keywords: mesomorphic materials; metallo-mesogens; silver complexes; π–π stacking; crystalline solids mesomorphic materials; metallo-mesogens; silver complexes; π–π stacking; crystalline solids
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Torres, I.; Ruiz, M.; Phan, H.; Dominguez, N.; Garcia, J.; Nguyen, T.-Q.; Evans, H.; Resendiz, M.J.; Baruah, T.; Metta, A.; Arif, A.; Noveron, J.C. Mesomorphic Behavior in Silver(I) N-(4-Pyridyl) Benzamide with Aromatic π–π Stacking Counterions. Materials 2018, 11, 1666.

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