Facile One‐Step Growth and Patterning of Aligned Squaraine Nanowires via Evaporation‐Induced Self‐Assembly

Abstract

Organic 1D nanomaterials based on low-molecular-weight semiconducting organic compounds are of interest because they possess unique properties for use in electronic, optoelectronic, and photonic nanodevices.[1] Different organic materials and methods have been employed to synthesize 1D single-crystal nanostructures. [2] While there are reports on fabricating organic 1D single crystals on specific device platforms, [3] relatively few of these reports deal with aligned organic 1D nanostructures [4] because they are complex to pattern; [5] often requiring templates, an external electric field, or surface-invasive steps. Consequently, simple patterning and aligning methods of 1D crystals are highly desirable in the pursuit of low-cost, large-scale fabrication of parallel device arrays. Here, we report a one-step method that can enable the growth, alignment, and periodic patterning of organic 1D single-crystal nanowires on a solid substrate. This method combines the processes of solvent-evaporation-induced selfassembly, contact line pinning, and dewetting, thus promising to be a simple and versatile approach to prepare sophisticated nanostructures. [6,7] To demonstrate the efficiency of the method we choose a squaraine dye, 2,4-bis[4-(N,N-dimethylamino)phenyl]squaraine (SQ), as model organic semiconductor, because squaraines are a novel class of organic dyes for photonic applications such as imaging, nonlinear optics, photovoltaics, biological labeling, and photodynamic therapy.[8] Both ground and excited states of SQ are intramolecular donor-acceptor-donor charge-transfer (D-A-D CT) states and have been studied theoretically.[9] SQ molecules easily form aggregates in a ''slipped stack'' arrangement because of strong intermolecular interactions between the acceptor (A) and the donor (D) groups (Fig. S1 in the Supporting Information). [10] As it has been shown that strong donor-acceptor dipole-dipole intermolecular interactions can direct the growth of 1D nanostructures, [11] we expect SQ also to have a strong tendency to form 1D nanostructures under appropriate conditions. We report here the preparation of SQ nanostructures by solvent evaporation on a horizontal substrate. In a typical experiment, a drop of SQ/CH 2 Cl 2 solution (0.02 mM, about 10 mL) was placed on a silicon substrate at 20 8C. After complete evaporation of solvent, the substrate was examined by scanning electron microscopy (SEM). As shown in Figure 1a, many nanowires were deposited on the substrate. The majority of the nanowires had a length of about 40 mm and a diameter of 100-300 nm. The dimensions of the nanowires were found to be sensitive to the surface morphology of the substrate, temperature, and evaporation rate. However, under a saturated vapor environment, no nanowires formed on the substrate after solvent evaporation.The morphology of the nanowires was further characterized by transmission electron microscopy (TEM; Fig. 1b), which shows that the SQ nanostructures are solid wires of nanometer diameter. The nanowires are single-crystall...

Photochromic Nanostructures Based on Diarylethenes with Perylene Diimide

“…23 Considering the molecular structure of 1, the dipole-dipole interaction is proposed to be the dominating driving force for the morphology transition from 0-D to 1-D, similar to the 1-D growing progress of an ICT compound. [24][25][26][27][28] For 1, the main transition dipole moment is along the long molecular axis ( Figure 8, 21 ), according to the calculation results and consistent with the results interpreted by W€ urthner et al, 17 which will direct the morphology transition process. Besides, the dipole-dipole interaction between the stacked thiophene rings should facilitate the transition simultaneously.…”

Organic nanofibers from squarylium dyes: local morphology, optical, and electrical properties

“…Such a red-shift is typical for J aggregates which are stabilized by intermolecular charge-transfer interactions between the electrondeficient squarylium moieties with the electron-rich dimethylamino phenyl groups. 7 Conversely, the absorption of the purple vapor deposited film is blue-shifted compared to the absorption in solution, which is attributed to the formation of H aggregates. These are believed to result from the alignment of the transition dipole moments, enforcing a 'face-to-face' stacking of the molecules.…”

“…6 Recently, the formation of aligned organic nanowires from squaraines via evaporation-induced self-assembly has been demonstrated. 7,8 The performance of polymeric materials commonly used in photovoltaic applications 9, 10 depends on, e.g., their regioregularity and polydispersity, factors that make their synthesis and purification difficult and scarcely reproducible. In particular, semiconducting polymeric materials are mostly obtained through metal catalyzed cross-coupling reactions.…”

Single‐Step Assembly of Large‐Area, Transparent Conductive Patterns Induced Through Edge Adsorption of Template‐Confined Au‐Thiocyanate

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been applied for creating microscale surface organization.[ 8 ] Related metal patterning technologies based upon evaporationinduced self-alignment, [9][10][11] direct laser sintering, [12][13][14] and micro-(or nano-) transfer molding have been also reported. [15][16][17][18][19][20][21] However, these techniques also generally require that metallic nanostructures (i.e., nanorods, nanowires, etc.)

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