Understanding the Metal-Directed Growth of Single-Crystal M-TCNQF₄ Organic Nanowires with Time-Resolved, in Situ X-ray Diffraction and First-Principles Theoretical Studies

Abstract

The deterministic growth of oriented crystalline organic nanowires (CONs) from the vapor-solid chemical reaction (VSCR) between small-molecule reactants and metal nanoparticles has been demonstrated in several studies to date; however, the growth mechanism has not yet been conclusively understood. Here, the VSCR growth of M-TCNQF(4) (where M is Cu- or Ag-) nanowires is investigated both experimentally and theoretically with time-resolved, in situ X-ray diffraction (XRD) and first-principles atomistic calculations, respectively, to understand how metals (M) direct the assembly of small molecules into CONs, and what determines the selectivity of a metal for an organic vapor reactant in the growth process. Analysis of the real-time growth kinetics data using a modified Avrami model indicates that the formation of CONs from VSCR follows a one-dimensional ion diffusion-controlled tip growth mechanism wherein metal ions diffuse from a metal film through the nanowire to its tip where they react with small molecules to continue growth. The experimental data and theoretical calculations indicate that the selectivity of different metals to induce nanowire growth depends strongly upon effective charge transfer between the organic molecules and the metal. Specifically, the experimental finding that Cu ions can exchange and replace Ag ions in Ag-TCNQF(4) to form Cu-TCNQF(4) nanowires is explained by the significantly stronger chemical bond between Cu and TCNQF(4) molecules than for Ag, due to the strong electronic contribution of Cu d-orbitals near the Fermi level. Understanding how to control the VSCR growth process may enable the synthesis of novel organic nanowires with axial or coaxial p/n junctions for organic nanoelectronics and solar energy harvesting.

Galvanic Replacement of Semiconducting CuTCNQF 4 with Ag + Ions to Enhance Electron Transfer Reaction

“…Additionally, the standard reduction potential for Ag + /Ag 0 couple is ≈ 0.8 V ( vs . SHE) . This suggests that the difference in the redox potentials provides enough driving force for a thermodynamically favourable spontaneous GR reaction.…”

“…Interestingly, the last decade has seen a rise in the use of the fluorinated analogue of TCNQ viz . 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (TCNQF 4 ) due to its superior optical, electrical, and magnetic properties in comparison to TCNQ‐based charge transfer complexes ,. Although the fluorinated analogues were primarily explored for field emission and switching devices, recent work by our group and others have shown the potential of MTCNQF 4 (where M=Cu or Ag) to be used as catalysts for electron transfer reactions between ferricyanide and thiosulfate, as well as for the conversion of Cr 6+ to Cr 3+ reduction in the presence of methanol as electron donor ,.…”

Engineering of Printable and Air‐Stable Silver Electrodes with High Work Function using Contact Primer Layer: From Organometallic Interphases to Sharp Interfaces

“…Previous works have shown that metalorganic Ag-F 4 TCNQ complexes are indeed formed upon hightemperature sintering or solution-based processing, where an intercalation of silver into the organic film was reported. [30][31][32] It was further found that these complexes exhibit optical characteristics that differ from those of the bare molecular material. [31,33] Therefore, we have also recorded optical absorption spectra of the F 4 TCNQ/Ag system to characterize the formed species with enhanced stability.…”

“…Compared to F 4 TCNQ, for which both the work function change of metal substrates by adsorption of molecular thin films and the formation of Ag-F 4 TCNQ complexes in the bulk have been reported, [15,16,30,31] the interaction of F 6 TCNNQ with metals has so far been much less investigated. With regard to its use as a contact primer, however, F 6 TCNNQ seems to be even more promising, since it leads to a higher work function (see Section 2.6), while its larger molecular mass suggests reduced diffusion into OSCs.…”

Nanophase Engineering of Organic Semiconductor-Based Solar Cells

“…Moreover, this quasi-one-dimensional morphology promises to also overcome the anisotropic transport limitations of small-molecule thin films, offering much higher mobilities and directional transport for improved photovoltaic efficiencies. Recently, Xiao et al [102] synthesized organic crystalline nanowires of CuPc and metal-7,7,8,8-tetracyanoquinodimethane (TCNQ) [103] with highly efficient charge transport and effective optical absorption in a well-controlled manner using different vapor-phase techniques, including vapor-solid chemical reactions and vapor-phase deposition [102,103]. The nanowires grow with the planar molecules π-π stacked along their length and could be grown in aligned arrays with these conducting axes aligned perpendicularly to the substrate in a suitable direction for carrier transport required for photovoltaic cells [104].…”