New fluorene–xanthene-based hybrid electrochromic and fluorescent polymers via donor–acceptor approach

Two novel donor–acceptor type, spiro-configured, fluorene derivatives 3′,6′-bis(octyloxy)-2,7-di(thiophen-2-yl)spiro[fluorene-9,9′-xanthene] (TXT) and 2,7-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-3′,6′-bis(octyloxy)spiro[fluorene-9,9′-xanthene] (EXE) have been synthesized and then electropolymerized via potentiodynamic and potentiostatic methods.Optical and electrochemical properties of their polymers, poly(3′,6′-bis(octyloxy)-2,7-di(thiophen-2-yl)spiro[fluorene-9,9′-xanthene]) (PTXT) and poly(2,7-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-3′,6′-bis(octyloxy)spiro[fluorene-9,9′-xanthene]) (PEXE) were investigated and it was found that polymers exhibit reversible redox behavior (Eonset·Oxd = 0.85 V for PTXT, Eonset·Oxd = 0.08 V for PEXE) accompanied with a reversible electrochromic behavior, yellow to green for PTXT, scarlet red to turquoise green with different intermediate colors for PEXE. The band gaps of the polymers were found to be 2.23 eV and 1.74 eV for PTXT and PEXE, respectively. PTXT was also prepared via chemical polymerization and the obtained polymer was found to display blue light emission in chloroform with a relatively high quantum yield (Φf = 0.59 in cyclohexane) despite having bluish-green light emission in the solid state. Both PTXT and PEXE are thermally stable with decomposition temperatures above 300 °C.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Electrochemical synthesis of new donor–acceptor type containing spiro-fluorene are highlighted. ► The polymer films exhibit reversible electrochromic behavior during p-doping. ► In chloroform, PTXT emits blue light when excited at 365 nm.