N,N-dimethylamino-phenylene–acetylene scaffolding: Structure–property relationships

• A novel substituted phenyleneethynylene was designed and synthesized.
• Spectral, photo-physical characteristics and INDO/S calculation were performed.
• The most bathochromically shifted bands have CT character.
• Non-planar molecules showed large changes in dipole moment between S0 and Sx states.
• For planar molecules, qF significantly quenched with increasing solvent, polarity.

Seven model donor-substituted phenyleneethynylene molecules with up to three 1,4-phenylene and two acetylenic units were synthesized by Suzuki–Miyaura and Sonogashira cross-coupling reactions and further studied by absorption and emission spectra and theoretical calculations. The π-system between the N,N-dimethylamino group and terminal acetylene was systematically elongated which allowed elucidation of the fundamental structure–property relationships. Structural factors such as molecular length and chromophore planarity proved to be crucial for the observed spectroscopic behavior.

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