Ordering of monomers, dimers and polymers of deposited Br₂I₂Py molecules: a modeling study

We propose a lattice model describing the ordering of 1,6-dibromo-3,8-diiodopyrene (Br₂I₂Py) molecules on the Au(111) surface into two-dimensional structures and correlated one dimensional rows. Our model employs three (intact, singly and doubly deiodinated) types of Br₂I₂Py molecules and mimics the situation which occurs with increasing temperature, where the majority of intact molecules form ordered two-dimensional networks, while most of the doubly deiodinated molecules assemble into long organometallic polymeric rows. We use DFT calculations to determine the values of intermolecular interactions for intact molecules and propose a strategy for estimating the interactions for deiodinated molecules, where the organometallic interaction with Au atoms plays the dominant role. Our model is solved using Monte Carlo calculations and allows us to obtain the monomeric structure of intact molecules, the dimeric structure of singly deiodinated molecules and the polymeric row structure of (mostly) doubly deiodinated molecules. We obtain the coexistence of ordered intact Br₂I₂Py molecules and organometallic dimers, as well as their separation at large values of intermolecular interaction with Au. Similar results are obtained by studying mixtures of singly and doubly deiodinated molecules: dimer rows can be either incorporated into the two dimensional pattern of correlated polymeric chains or separated into their own dimeric structures.