Retro-Diels-Alder Reaction on Surface: Generating Energy-Prohibited Structures in Bulk Film Condition through Surface-Adsorbing Neutralization Effect

Retro-Diels-Alder (rDA) reactions on surfaces were few reported in comparison with the fruitful results of rDA in liquids, gas phase or bulk films. On the other, the important effects of inert substrates on surface reactions were failed to be recognized clearly in current researches either although the influences of active metal substrates on varied surface reactions have been researched widely. Herein, the stepwise rDA reactions of tetrabicyclo[2.2.2]octadienoporphyrin on graphite surface were investigated through scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. Besides the final product, several other types of topographies were revealed at sub-molecular level in the STM micrographs, including the bright rod (R), bright triangle (T) and mini triangle (mini-T). Combining STM results with DFT data allows the reasonable intermediates and pathways in each step of surface rDA to be recognized definitely. The structures corresponding to the R, T and mini-T topography were i...