Ethynylene‐Bridged Pentacene Trimer and Tetramer Prepared Through Unexpected Oligomerization and Their Subsequent Thermal Conversions

Abstract Ethynylene‐bridged acenes, which are π‐conjugated triple bond‐containing systems, have attracted increasing interest as promising organic semiconductor materials due to their delocalized π‐electrons. In this study, ethynylene‐bridged pentacene precursor oligomers were not only synthesized through multiple‐organic reactions but also were unexpectedly obtained in one‐pot by using a conventional reaction with lithium silylacetylide and quinone. In the case of one‐pot synthesis, the formation of oligomers, including pentamer, was evidently confirmed by matrix‐assisted‐laser‐desorption/ionization time‐of‐flight mass spectrometry. Single crystal X‐ray analysis visualized the ethynylene‐bridged structure of the dimer which was one of the major products in the one‐pot reaction. It was found that the reaction time for the lithiation was the key factor in controlling oligomer formation. Finally, the thermal conversion from pentacene precursors to the corresponding pentacene oligomers was achieved via retro ‐Diels–Alder reaction. These results would open an access to synthesize a wide range of π‐conjugated systems.