Molecular imaging of polyimide formation

Abstract

The reactions of 3,4,9,10-perylenetetracarboxylic dianhydride with 4,4'-diamino-p-terphenyl and with 2,4,6-tris(4-aminophenyl)-1,3,5-triazine on an Au(111) surface have been followed by low-temperature UHV-STM in the range of 300 to 700 K at coverages of up to one monolayer. Well-ordered, H-bonded structures are observed even after annealing at temperatures up to 470 K, while above 550 K reaction is initiated with evidence of amic acid intermediates. At higher temperatures, full imidisation leads to a covalently linked, surface polyimide networks. There is evidence of gold reconstruction playing a role in the early stages of imidisation and signs of limited order in the final polyimide. With the diamine as precursor, 1D-interconnectivity results, while with the triamine as partner, full 2D-connectivity is possible. In contrast to the situation in the bulk, the intermediate amic acid seems to be less stable and iso-imides are common in the final networks, as witnessed by the conformation of the product and the prevalence of triangular features in the case of the polyimide formed from the triamine precursor.

Surface Science Approaches to Molecular Nanostructures

“…6A). [60,61] In solution and in thin films, the amic acid reaction intermediate is readily formed at room temperature, whereas on Au(111) structures ascribed to amic acid species (Fig 6B) can only be observed after annealing to above ~470 K. [61] As outlined in the previous section, below this temperature, the two species form highly ordered nanostructures stabilized by hydrogen bonds. [50] The restriction of the two reaction partners to two dimensions hence considerably raises the activation barrier for the first reaction step which is intuitively plausible since the nucleophilic backside attack involved in this step requires an offset between the reaction partners, which might only be reached at higher temperatures where vibrational amplitudes of either of the reactants orthogonal to the surface become significant.…”

“…This smaller size might be due to kinetic limitations during growth and/or to steric hindrance. Interestingly, the confinement of the imidization condensation reaction to the surface appears to increase the proportion of iso-imide reaction products, [61] where the nitrogen has replaced the carbonyl oxygen instead of the bridging oxygen in the final product. This is tentatively ascribed to a lower strain energy of both the intermediate and final reaction products of the iso-imide in the constrained geometry on Au(111).…”

“…This is tentatively ascribed to a lower strain energy of both the intermediate and final reaction products of the iso-imide in the constrained geometry on Au(111). [61] The overall topographic properties of the polymeric network can be influenced by changing the reaction partners. While the linear DATP leads to locally close-packed films of one-dimensionally interconnected oligomers ( Fig.…”

Enantioselective Heterogeneous Catalysis

“…In particular, one can envisage the construction of 2D nanoporous H-bonded networks, MOFs, or architectures constructed via controlled covalent assembly. Many examples exist of such architectures formed both under UHV conditions [81][82][83][84][85][86][87] and at the liquid-solid interface [88][89][90][91]. Pores designed to have a suitable (chiral) shape and dimension could act as hosts for prochiral reagents.…”

Chemical reactivity on surfaces: Modeling the imide synthesis from DATP and PTCDA on Au(111)

“…Recently it was demonstrated that polyimide strands can be formed from a hydrogen-bonded PTCDA-DATP superstructure on Au͑111͒ by annealing. 22,23 From these experiments it was concluded that the confinement to the surface raises the energy barrier to form the amic acid reaction intermediate, cf. scheme in Fig.…”