Abstract
Dendrimers are homostructural and highly branched macromolecules with unique dendritic effects and extensive use in multidisciplinary fields. Although thousands of dendrimers have been synthesized in solution, the on-surface synthetic protocol for planar dendrimers has never been explored, limiting the elucidation of the mechanism of dendritic effects at the single-molecule level. Herein, we describe an on-surface synthetic approach to planar dendrimers, in which exogenous palladium is used as a catalyst to address the divergent cross-coupling of aryl bromides with isocyanides. This reaction enables one aryl bromide to react with two isocyanides in sequential steps to generate the divergently grown product composed of a core and two branches with high selectivity and reactivity. Then, a dendron with four branches and dendrimers with eight or twelve branches in the outermost shell are synthesized on Au(111). This work opens the door for the on-surface synthesis of various planar dendrimers and relevant macromolecular systems.
Highlights
Dendrimers are homostructural and highly branched macromolecules with unique dendritic effects and extensive use in multidisciplinary fields
Ever since the first cascade molecules, and nee dendrimers reported by Vögtle et al in 19782, thousands of dendrimers have been developed in solution[3,4,5], which exhibit a variety of unique dendritic effects and lead to extensive use in multidisciplinary fields[6,7,8,9,10,11,12]
The experimental results showed that no cross-coupling occurred between the porphyrin derived aryl bromide and isocyanide on Au(111) after annealing to 403 K
Summary
Dendrimers are homostructural and highly branched macromolecules with unique dendritic effects and extensive use in multidisciplinary fields. We describe an on-surface synthetic approach to planar dendrimers, in which exogenous palladium is used as a catalyst to address the divergent crosscoupling of aryl bromides with isocyanides This reaction enables one aryl bromide to react with two isocyanides in sequential steps to generate the divergently grown product composed of a core and two branches with high selectivity and reactivity. Planar dendrimers synthesized in situ on surfaces could afford unambiguous configurations in the two-dimensional confined space, which are beneficial to elucidate the mechanism of dendritic effects at the single-molecule level and produce highly ordered, self-assembled structures. The in situ synthesis of dendrimers on surfaces solves the problems of solubility and sublimation caused by their high molecular weight
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