Synthesis, characterization and optical properties of novel well-defined di(1-ethynylpyrene)s

Three di(ethynylpyrenes) were synthesized and characterized: (Z)-1,1′-(buta-1,3-diene-1,3-diyl)dipyrene (DEPS), (E)-1,1′-(buta-1,3-diene-1,3-diyl)dipyrene (DEPA) and 1,1′-(but-3-ene-1,3-diyl)dipyrene (DEPH). The optical properties of these oligomers were studied by absorption and fluorescence spectroscopies and the results were compared to those previously obtained for the related polymer trans-poly(1-ethynylpyrene) (trans-PEP). Intramolecular interactions occur between adjacent pendant pyrene units (associated pyrenes) in DEPS and DEPH, giving rise to static excimer emissions resulting from the stacking of aromatic rings. Excitation spectra jointly with life time fluorescence decays proved that such interactions take place in the ground state.