Multifunctional geometrical isomers of ferrocene-benzo[1,2-b:4,5-b′]difuran-2,6-(3H,7H)-dione adducts: second-order nonlinear optical behaviour and charge transport in thin film OFET devices

Abstract

Geometrical isomers of a set of new ferrocene-benzo[1,2-b:4,5-b′]difuran-2,6-(3H,7H)-dione dyads were synthesized and their optical, nonlinear optical (NLO) and electrochemical properties were investigated. The compounds were fully characterized by spectroscopic data and single crystal X-ray analysis in few cases. The second-order nonlinear polarizabilities were measured in chloroform using a femtosecond hyper-Rayleigh scattering (HRS) method at 1300 nm. The dyads exhibit structure-dependent NLO properties, which could be rationalized by correlation with electrochemical and theoretical data. The (Z)-6 chromophore recorded higher β_HRS values than the corresponding (E)-6 isomer, in the donor–acceptor (D–A) type dyads. Similarly, in D–A–D chromophore 7, the β_HRS values of isomers follow the order (Z,Z) > (E,Z) > (E,E), which matches with the trend of the wavelength of their maximum absorption as well as an increasing band gap in that order. Owing to the inbuilt structural features, two of these D–A compounds were also explored as semiconducting materials in vacuum deposited top contact bottom gated thin film organic field-effect transistors (OFETs). Defying steric restrictions of the ferrocene unit, the triad (Z,Z)-7 depicted an unbalanced (μ_e: 3 × 10⁻³ cm⁻² V⁻¹ s⁻¹ and μ_h: 7 × 10⁻⁵ cm⁻² V⁻¹ s⁻¹) charge transport behaviour. Evaluation of the isomers of the type studied in this investigation constitutes one of very few reports, in particular this study reveals for the first time the semiconducting behaviour of thermally stable redox active Fc based semiconductors.