Oligo(3,6-phenanthrene ethynylenes): Synthesis, Characterization, and Photoluminescence

A series of highly fluorescent, oligo(3,6-phenanthrene ethynylenes) (F1-F7) were synthesized, and their photophysical behavior was systematically investigated. They emitted light with highly emissive quantum yields, up to 0.92. Emissive wavelengths of these compounds relied on the number of phenanthrene blocks existing in the oligomers. Red-shifted emissions were observed as the number of phenanthrenes increased. On the basis of theoretical calculations, helical structures could be formed for F4-F7, indicating that the excimer emissions might be observed for F4-F7 due to the intramolecular pi-pi stackings of phenanthrenes in the helical structures. However, excimer emissions were only observed for F5-F7 in dilute cyclohexane and for F6 and F7 in dilute methylene chloride, respectively. No excimer emission was observed for F4-F7 in dilute tetrahydrofuran due to the degree of solvation.