Ferrocenyl end capped molecular rods: synthesis, structure, and properties

A series of ferrocenyl phenylethynyl rods 1-11 were designed, and synthesized by a Pd catalysed Sonogashira cross-coupling, and oxidative homo-coupling reactions. The ferrocenyl moieties in the rods 1-11 are attached at the para/meta position of phenylethynyl unit or at the acetylenic unit. The effect of enhancing the conjugation, and connectivity (meta/para) on the photonic and electrochemical properties were explored. The para linkage, and butadiynyl linkage lower the band gap in the rods. The meta linked ferrocenyl phenylethynyl rods 2, 4, and 10 show good HOMO-LUMO separation compared to para linked rods 1, 3, 9. The single crystal X-ray structures of rods 2, 4, 10, 14 and 19 are reported. The ferrocene units in rods 2, 4, and 10 are in a trans configuration with respect to the phenyl ring.