Excimer formation from particially overlapped anthracene dimer based on saddle-shaped cyclooctatetrathiophene as spacer

[Display omitted] •Excimer formation is confirmed from twisted and particially overlapped anthracene dimer.•One of saddle-shaped cyclooctatetrathiophene isomers, tetra[3,4-Thienylene] (TT) is employed as a rigid 3D spacer for anthracene dimer.•The crystal structure gives the direct evidence for the formation of the novel excimer. With “saddle” shaped tetra[3,4-Thienylene] (TT) as a rigid 3D spacer, three anthryl substituted TT compounds, 1-(anthracen-9-yl)[3,3′-bithiophene] (TTA-1), 1,7-di(anthracen-9-yl)-[3,3′-bithiophene] (TTA-2) and 1,12-di(anthracen-9-yl)[3,3′-bithiophene] (TTA-3) were designed and synthesized. Their physical behaviors including NMR spectra, crystal structures and spectroscopic properties were studied. Due to the steric hindrance from TT moiety to avoid the dimer formation between molecules, TTA-1 and TTA-2 show monomer anthracene emission both in solution and rigid state, and a mixture of monomer and excimer emission in aggregation state. Bearing two ipsilateral anthracene moieties in molecule, TTA-3 gives a twisted and end-overlapped dimer in the ground state, and shows excimer emission only in solution, aggregation state and rigid state. In addition, a model compound, 2,2′-di(anthracen-9-yl)-5,5′-di(trimethylsilyl)-[3,3′-bithiophene] (BTA) was prepared, which shows monomer emission in both solution and rigid state, but gives excimer emission in the aggregation due to its extended conformation in solution and intermolecular dimer arrangement in its crystal and aggregation state.