Synthesis and optical properties of novel D–π–A–π–D type cationic cyclopentadienyliron complexes of arenes

Abstract

Diphenylethynyl chromophores were successfully introduced into the arene ligands of cationic cyclopentadienyliron complexes through nucleophilic substitution and Suzuki coupling reactions. Three novel cationic cyclopentadienyliron complexes with symmetrical di(4-methoxy-phenylethynyl) chromophores (CFSs) were obtained and completely characterized by IR, ¹H NMR, ¹³C NMR, and MS. The linear and nonlinear optical properties of the obtained molecules were tuned using phenylethynyl linkages. The UV-Vis absorption spectra showed that increasing the conjugation by substituting phenylacetylene spacer resulted in a red shift in the absorption bands and a stronger absorption in CFSs than in the previously reported (η⁶-cumene)(η⁵-cyclopentadienyl)iron hexafluorophosphate (I-261). These cross-conjugated D–π–A–π–D type compounds also showed larger third-order nonlinear susceptibility than I-261.