Structure–Property Relationship in an Organic Semiconductor: Insights from Energy Frameworks, Charge Density Analysis, and Diode Devices

Abstract

A lightweight organic material, trans-4′-dimethylamino-4-nitro-α-cyanostilbene, exhibits notable charge carrier mobility (∼10–4 cm2 V–1 s–1). The non-centrosymmetric material also displays moderate second harmonic generation activity. This is one of the rarest examples of small organic materials displaying semiconductor characteristics. The charge-transfer pathway as elucidated via high-resolution single-crystal X-ray diffraction data based “energy frameworks” and “experimental charge density” analyses is assessed by measuring the charge carrier mobility using the space charge limited current technique on pure single-crystal diode devices. These advanced structural analyses clearly demonstrate that charge transport in organic crystals is purely governed by its molecular packing, especially the π–π stacking geometry. The balanced ambipolar charge transport behavior makes this highly soluble and thermally stable organic crystal promising for applications in optoelectronic devices. Moreover, this report introduces the crucial role of energy frameworks and charge density analyses for fundamental understanding of the structure–property relationship in organic semiconductors.

Probing Diversity in Binding Affinities of Polymorphs of an Anticancer Agent against Human γ-Enolase: A Quantum Crystallographic Perspective

“…In all three cases, the scale factors vary only by 2–4% with respect to the resolutions of the diffraction data, and the distributions of the experimental and expected residuals are in good agreement. The quality of the multipole model and the data are in good agreement with those reported in the literature. , The atom labeling scheme (Figure ) as followed for 1a is also followed for 1b and 1c . The Hirshfeld rigid bond test applied for each pair of non-H atoms resulting the largest values of the difference between the components of the U ij tensor along the bond are 8 × 10 –4 Å 2 for N3–C17 and N3–C16 bonds in 1a , 8 × 10 –4 Å 2 for N3–C16 bond in 1b , and 9 × 10 –4 Å 2 for N1–C5 bond in 1c , which are well within the acceptable limit of 10 –3 Å 2 .…”

Using Density Functional Theory to Correlate Charge Transport Properties with Gas Sensing by Organic Nanowires

“…The molecule is found to be packed in cofacial 1D π-stacking. Molecular packing in the form of cofacial π-stacking is more favorable for the efficient charge transport than the herringbone or 2D brick layer packing due to the larger π-orbital overlapping . This type of 1D self-assembly of molecules is the primary requirement to realize a host of one-dimensional organic nanostructures such as nanowires, nanoribbons, etc .…”

“…To study the charge transfer properties (hole and electron mobility) of any organic semiconductor, the knowledge of the crystal packing motif is the primary requirement. We predicted the crystal structure, viz., the molecular packing, of our newly designed NNDMNH 2 molecule by employing density functional theory in which the experimental crystal structure of trans -4-nitro-4′-dimethylamino-α-cyanostilbene (NNDMCN) was used as the initial guess since these two molecules differ only by one functional group in their π-conjugated backbones. Starting from the experimental crystal structure of the NNDMCN as mentioned, we optimized the unit cell of NNDMNH 2 using the method of steepest descent (conjugate gradient algorithm) as implemented in the plane wave DFT code VASP. − The optimization procedure was carried out within the generalized gradient approximation with van der Waals corrections [optimized Perdew–Burke–Ernzerhof vdW (optPBE-vdW)] in several steps, including ion relaxation, change of cell shape, and change of cell volume, or a combination of these parameters to attain the ground state structure.…”

“…To study the charge transfer properties (hole and electron mobility) of any organic semiconductor, the knowledge of the crystal packing motif is the primary requirement. We predicted the crystal structure, viz., the molecular packing, of our newly designed NNDMNH 2 molecule by employing density functional theory in which the experimental crystal structure of t r a n s -4 -n i t r o -4 ′ -d i m e t h y l a m i n o -α -c y a n o s t i l b e n e (NNDMCN) 16 was used as the initial guess since these two molecules differ only by one functional group in their πconjugated backbones. Starting from the experimental crystal structure of the NNDMCN as mentioned, we optimized the unit cell of NNDMNH 2 using the method of steepest descent (conjugate gradient algorithm) as implemented in the plane wave DFT code VASP.…”

“…Molecular packing in the form of cofacial π-stacking is more favorable for the efficient charge transport than the herringbone or 2D brick layer packing due to the larger π-orbital overlapping. 16 This type of 1D selfassembly of molecules is the primary requirement to realize a host of one-dimensional organic nanostructures such as nanowires, nanoribbons, etc. 15 NNDMNH 2 crystal shows potentiality in this regard by its strong structural resemblance to PTCDI, 36 which is one of the prominent candidates for the synthesis of organic nanostructures.…”