On-Surface Reaction of 1,4-Dibromo-2,5-Diiodobenzene on Au(111) and Ag(100)

The on-surface reaction processes of 1,4-dibromo-2,5diiodobenzene (C6H2Br2I2) on Au(111) and Ag(100) were systematically investigated under ultra-high vacuum conditions by using scanning tunneling microscopy. Deiodination underwent at RT on both surfaces with the formation of organometallic intermediates connected by C-Au-C and C-Ag-C linkages. In particular, partial deiodination on Au(111) resulted in self-assembled ordered structures of organometallic trans-trimers, which were converted into longer organometallic chains after complete deiodination at 100 degrees C. On Ag(100), complete deiodination gave rise to disordered molecular clusters at RT and organometallic intermediates were formed via the debromination process after annealing to 150 degrees C. Further annealing to higher temperatures resulted in covalent C-C bonded polyphenylene chains and finally disordered graphene nanostructures via cyclodehydrogenation. Our study provides fundamental comprehension of temperature-selective on-surface dehalogenation reactions of multi-halogen-substituted precursors for constructing designer covalently bonded networks.