Synthesis, photophysical and electrochemical properties of π-conjugated pyrene based down-shifting molecules with fluorinated aryl groups

Abstract

Pyrene molecule, with excellent photophysical properties (strong absorption cross section, excellent emission properties and a long-excited state lifetime), excellent thermal and photochemical stability, has been widely used as a building block for the synthesis of pyrene-based fluorophores for optoelectronic applications. In this work, we report the synthesis of two series of pyrene–π–A compounds, series I (3–6) and II (10–13), in which nitro, cyano, cyanoacrylonitrile and cyanoacrylic acid as electron acceptor groups are connected to the pyrene core via aryl or fluoroaryl π-conjugating bridges. The incorporation of fluorine atom on the π-extension bridge cause a slightly red-shift at emission wavelength (λem) in solution and polymethylmethacrylate (PMMA) films and increase the Stokes shift due to greater stabilization of molecular orbitals in the excited state, especially for series I. Solvatochromic measurements and theoretical computational studies suggest a higher intramolecular charge transfer in the excited state for series II when compared to series I due to their stronger electron acceptor moieties. All pyrene derivatives are stable and exhibited initial mass loss at temperature above 200 °C. The good photophysical and thermal properties of the synthesized pyrene derivatives, associated with high molar absorption coefficients in the UV spectrum and good fluorescence emission in the range of 430–480 nm (series I) and 505–567 nm (series II) in PMMA films, make them possible candidates for organic light-emitting diode (OLED) and luminescent down-shifting (LDS) layers for stable perovskite solar cells, respectively.