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

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.

Manifestations of Antiaromaticity in Organic Materials: Case Studies of Cyclobutadiene, Borole, and Pentalene

“…[127] In 2020, de la Torre et al synthesized pentalene-bridged bisanthene on a gold surface and monitored the reaction by STM and AFM (Figure 19). [128] The on-surface polymerization led to a maximum length of twelve repeating units, with two isomers equally probable. Spatially resolved electronic measurements revealed that the polymer had a valence band at À 0.6 eV and a conduction band at 0.5 eV, resulting in a low band gap of ~1.1 eV.…”

“…Polymer 132 was deposited on an Au(111) surface, and upon annealing, polymers containing fused dibenzopentalene units were formed (one isomer is shown). nc-AFM/STM images adapted from Ref [128],. Copyright (2020), with permission from Springer Nature Limited.…”

π‐Extendedperi‐Acenes: Recent Progress in Synthesis and Characterization

“…Upon further annealing at 650 K, the 117 wire underwent two-fold cyclization reaction between adjacent bisanthene moieties and obtained a long pentalenebridged conjugated ladder polymer. [103] In 2020, they further extended this chemistry to build one-dimensional cumulenelike polymers 118 based on [5,2]PA units. [104] Towards the synthesis of 118, on-surface reactions of 13,13'bis(dibromomethylene)-13H,13'H-6,6'-bipentacenylidene precursor (41) was performed on Au(111) under UHV conditions (Figure 27g).…”

Einsatz der kooperativen Katalyse für die Oberflächensynthese linearer heteroaromatischer Polymere durch selektive C‐H‐Aktivierung

“…Tatsächlich wurde kürzlich gezeigt, dass solche mobilen Adatome, die bei hohen Temperaturen häufig auf Metalloberflächen vorhanden sind, wichtige Reaktionsschritte wie die tautomere Dehydrierung von Keto-Enol, [40] und die C-C-Kopplung fördern. [41][42][43] Daher haben wir QM/MM [44] -Berechnungen der freien Energie mit der WHAM-Methode [45] durchgeführt, um diese Hypothese zu untersuchen. Tatsächlich zeigen die QM/MM-Simulationen eine erhebliche Verringerung der Aktivierungsenergien um � 60 kcal mol À 1 .…”