Why are Fluorene-Containing Materials so Versatile? An Electronic Structure Perspective

The HeI/HeII photoelectron spectra of substituted fluorenes (2-aminofluorene, 2,7-dibromofluorene, 2-acetylfluorene, and 9-trimethylsilylfluorene) are reported for the first time. We have observed significant changes in the π-electronic structure of the title molecules on substitution at 2-, 7-, and 9-positions and interpreted them within the theoretical framework of resonance and inductive effects. The substituents attached to fluorene at these positions govern the photophysical behaviour and properties of polymetallaynes that contain the fluorene moiety. The mediated properties include the size of the polymer bandgap, various non-linear optical properties, and the intensity and lifetime of luminescence processes. Our spectral results provide some detailed explanations of substituent influences in the form of, for example, orbital ionization energies, which can be further related to charge-transfer processes present in these metallo-organic polymers.