Tailoring \u03c0-conjugation and vibrational modes to steer on-surface synthesis of pentalene-bridged ladder polymers

Bruno De La Torre,Rodolfo Miranda,Eider Rodríguez-Sánchez,Jesús I Mendieta-Moreno,Miroslav Medveď,Benjamin Mallada,Michal Otyepka,Ana Sánchez-Grande,José Santos,David Écija,Shayan Edalatmanesh,Nazario Martín,Koen Lauwaet,Pavel Jelínek,Borja Cirera,Álvaro Buendía,Adam Matěj

doi:10.1038/s41467-020-18371-2

Abstract

The development of synthetic strategies to engineer π-conjugated polymers is of paramount importance in modern chemistry and materials science. Here we introduce a synthetic protocol based on the search for specific vibrational modes through an appropriate tailoring of the π-conjugation of the precursors, in order to increase the attempt frequency of a chemical reaction. First, we design a 1D π-conjugated polymer on Au(111), which is based on bisanthene monomers linked by cumulene bridges that tune specific vibrational modes. In a second step, upon further annealing, such vibrational modes steer the twofold cyclization reaction between adjacent bisanthene moieties, which gives rise to a long pentalene-bridged conjugated ladder polymer featuring a low bandgap. In addition, high resolution atomic force microscopy allows us to identify by atomistic insights the resonance form of the polymer, thus confirming the validity of the Glidewell and Lloyd´s rules for aromaticity. This on-surface synthetic strategy may stimulate exploiting previously precluded reactions towards π-conjugated polymers with specific structures and properties.

Highlights

The development of synthetic strategies to engineer π-conjugated polymers is of paramount importance in modern chemistry and materials science
To overcome these synthetic challenges, on-surface synthesis has emerged as a disruptive paradigm to develop chemical reactions on surfaces, while simultaneously monitoring and elucidating the precursors, intermediates and reaction products by means of scanning probe microscopy[14,15,16,17,18]
We report the synthesis and detailed atomistic characterization by a comprehensive scanning tunneling microscopy (STM) and non-contact atomic force microscopy supported by density functional theory (DFT) study of the on-surface reactions of two distinct molecular precursors, 4BrBiA [10,10′-bis(dibromomethylene)-10H,10′H-9,9′-bianthracenylidene] and 4BrAn [9,10-bis(dibromomethylene)-9,10dihydroanthracene]

Summary

Introduction

The development of synthetic strategies to engineer π-conjugated polymers is of paramount importance in modern chemistry and materials science. High resolution atomic force microscopy allows us to identify by atomistic insights the resonance form of the polymer, confirming the validity of the Glidewell and Lloyds rules for aromaticity This on-surface synthetic strategy may stimulate exploiting previously precluded reactions towards πconjugated polymers with specific structures and properties. Taking into account the aforementioned unique properties, it is of timely relevance to engineer conjugated ladder polymers incorporating non-benzenoid components, targeting to design chemically robust and low bandgap polymers. Such synthesis in wet chemistry must contend with structural defects and low solubility that prevent complete control over the synthesis and structural characterization at the atomic scale. Despite the recent progress in on-surface synthesis, there are still very limited strategies to synthesize complex π-conjugated polymers with specific properties[14,15,16,17,18,19,20,21,22,23,24,25,26,27]

Methods

Results

Conclusion