Effect of thermal annealing on hydrogen bond configurations of host lattice revealed in VOPc/TCDB host-guest architectures

The two-dimensional (2D) self-assembled 1,3,5-tris(10-carboxydecyloxy) benzene (TCDB) networks connected by hydrogen bonds are shown to accommodate molecules such as vanadyl phthalocyanine (VOPc) on highly oriented pyrolytic graphite (HOPG) surfaces when examined by scanning tunneling microscopy (STM) under ambient conditions. Thermally annealed adlayers were investigated with STM, which demonstrated that thermal annealing could induce a distinctive phase transition from the host-guest architecture VOPc/TCDB (II) (consisting of VOPc dimers or two VOPcs entrapped in one TCDB cavity) to the architecture VOPc/TCDB (I) (consisting of VOPc monomers or one VOPc entrapped in one TCDB cavity). On the basis of density functional theory (DFT) calculations, we suggest that the transition is associated with the transformation of the hydrogen bond configurations in the TCDB dimers. The experimental results combined with the theoretical calculations revealed that monomer-entrapped VOPc/TCDB (I) is thermodynamically stable for the VOPc/TCDB complex architectures.