A Two‐Dimensional Polymer Synthesized at the Air/Water Interface

Abstract

A trifunctional, partially fluorinated anthracene-substituted triptycene monomer was spread at an air/water interface into a monolayer, which was transformed into a long-range-ordered 2D polymer by irradiation with a standard UV lamp. The polymer was analyzed by Brewster angle microscopy, scanning tunneling microscopy measurements, and non-contact atomic force microscopy, which confirmed the generation of a network structure with lattice parameters that are virtually identical to a structural model network based on X-ray diffractometry of a closely related 2D polymer. The nc-AFM images highlight the long-range order over areas of at least 300×300 nm . As required for a 2D polymer, the pore sizes are monodisperse, except for the regions where the network is somewhat stretched because it spans over protrusions. Together with a previous report on the nature of the cross-links in this network, the structural information provided herein leaves no doubt that a 2D polymer has been synthesized under ambient conditions at an air/water interface.

Synthetic 2D Polymers: A Critical Perspective and a Look into the Future

“…After the many unsuccessful attempts aimed at elucidating molecular structure by HR‐AFM and STM of ex situ prepared covalent monolayers, it was exciting to the see the results obtained by Hinaut and Glatzel et al., who under UHV conditions and employing the second pass method obtained the beautiful HR‐AFM image of 2DP12 shown at the beginning of this article in Figure c . One can nicely recognize the highly regular array of pores extending over at least an area of 120 × 120 nm 2 as expected for a 2D polymer.…”

“…To confirm this presumed crystallinity, the polarizer angle was switched from a value of +2° to −2°, which resulted in a homogeneous contrast change of all islands in the image. This contrast change proves the orientation of the refractive index anisotropy to be constant over the entire islands . Together with the sharpness and jaggedness of the edges, the islands thus represent a cohesive, solid‐like phase, with a uniform orientation and density of the monomers in all these areas.…”

Bridging Length Scales by Photochemistry

“…This is related to the fact that in the monomer array all reactive sites are tightly arranged relative to one another to form “reactive pairs”; the groups have simply no other choice but to channel their excited state energy directly into the reaction with the reactive group of the neighbouring monomer. [2+2]‐, [4+4]‐ and [4+2]‐cycloadditions have so far been realized, employing trifunctional monomers . Note that this packing can easily result in disobeying the Woodward–Hoffmann rules.…”

Highly Crystalline and Semiconducting Imine‐Based Two‐Dimensional Polymers Enabled by Interfacial Synthesis

“…Particularly,u nder the presence of Lewis acid catalyst (Yb(OTf) 3 ), the resultant PI-2DP 1 film was fully crystalline with domain sizes of % 100 to 150 nm, which are one order of magnitude larger than the previously reported 2D polyimine films. [14] Thec rystal formation was probed by the ex-situ time-dependent TEM imaging. Thee xtended conjugation of the porphyrin moieties within a2 Dl ayer together with the high crystallinity of PI-2DP 1 make this as an attractive material for the fundamental investigation of charge carrier transport properties.Inthis context, ultraviolet photoelectron spectroscopy (UPS) and Te rahertz (THz) spectroscopy were employed to probe the intrinsic electronic properties of PI-2DP 1.T he resultant crystalline PI-2DP 1 exhibited ap-type semiconductor behavior with aband gap of 1.38 eV and am obility up to 0.01 cm 2 V À1 s À1 ,w hich is superior to the reported 2D polyimine films.T his work highlights the controlled synthesis of crystalline,l arge-area 2D polyimine films and provides the rational approach to ascertain structure-property relationships which will shed light on further developing semiconducting 2D polymer films with improved charge transport properties.…”

“…[11] In particular,a ir-water and liquid-liquid interfaces assisted synthesis offers ar eliable pathway to prepare large-area, single-/few-layer 2D polymers which can be easily transferred directly from the interface to various substrates for further characterization and device fabrication. [12][13][14] Fori nstance, large-area, imine-based 2D COF films (polyTB) with varied thickness from % 2t o2 00 nm were prepared at the DMF/air interface,w hich could function as as emiconductor layer in af ield-effect transistor (FET) device and exhibited ac harge carrier mobility of 3.0 10 À6 cm À2 V À1 s À1 . [15] We have previously explored the synthesis of polyimine-based 2DPs (PI-2DPs) at the air-water and liquid-liquid interfaces,w hich resulted in free-standing,s ingle-and multi-layer films, [14] respectively.T hen PI-2DP was integrated as an active semiconducting layer in at hin film transistor which displayed am obility of 1.3 10 À6 cm À2 V À1 s À1 .B esides the intrinsic low in-plane conjugation of polyimine,t he low mobility can be majorly attributed to the defect densities and small crystalline domain sizes ( % 10-20 nm) of the resultant 2D polyimine films.I tr emains challenging to further improve the crystallinity of PI-2DPs via such interfacial synthesis due to the lack of control over the ordered arrangement of the precursor monomers at the interface.M oreover,m any factors govern the performance of electroactive layers,a mong which the growth of long-range ordered crystalline 2D COF/2D polymer films plays ak ey role in influencing the charge-carrier transport properties.…”