Luminescence of fluorenes 2,7-conjugatively extended with pyrenylvinylene and pyrenylvinylene-phenylenevinylene

2,7-Bis(1'-pyrenylvinylene)-9,9-diethylfluorene (1) and 2,7-bis(1'-pyrenylvinylene- 4 ''-phenylenevinylene)-9,9-diethylfluorene (2) were synthesized and their static luminescence behavior assessed. They show solution photoluminescence (PL) maxima in chloroform at 475 nm and 467 nm, with quantum efficiencies of 54% and 52%, respectively. Double-layer LED devices with configuration ITO/PEDOT-PSS/(1 or 2)/Ca-Al emitted blue-green light with turn-on voltages of 2.5 V and emission maxima at 500 nm (2.48 eV); their luminance efficiencies were 0.36 and 0.30 cd A(-1), respectively. Blending of 1 at 20% (w/w) in PVK improved the luminance efficiency to 1.81 cd A(-1) for the same device configuration, with only a small increase in turn-on voltage to 3 V; the emission maximum was 497 nm (blue- green emission), the maximum luminance 7600 cd m(-2) with CIE color coefficients of (0.12, 0.45). For a 10% (w/w) blend of 2 in PVK using the same device configuration, the luminance efficiency was 1.47 cd A(-1), turn-on voltage 3 V, maximum luminance 2600 cd m(-2) with CIE coefficients of (0.13, 0.45). Simple p-MO calculations show that structural extension of the nominal conjugation length in 2 does not significantly decrease the effective band gap relative to 1, consistent with the observed lack of red shift in 2.