Highly photoluminescent and blue-green electroluminescent polymers: New silyl- and alkoxy-substituted poly(p-phenylenevinylene) related copolymers containing carbazole or fluorene groups
T. Ahn et al., Highly photoluminescent and blue-green electroluminescent polymers: New silyl- and alkoxy-substituted poly(p-phenylenevinylene) related copolymers containing carbazole or fluorene groups, MACROMOLEC, 33(18), 2000, pp. 6764-6771
A series of silyl- and alkoxy-substituted poly(p-phenylenevinylene) related
copolymers containing carbazole and fluorene groups, poly[9,9-n-dihexyl-2,
7-fluorenediylvinylene-alt-2,5-bis(trimethylsilyl)-p-phenylenevinylene] (PF
BTS-PPV), poly[N-ethylhexyl-3,6-carbazolevinylene-alt-2, 5-bis(trimethylsil
yl)-p-phenylenevinylene] (PCBTS-PPV), poly[9,9-n-dihexyl-2,7-fluorenediyl-v
inylene-alt-2-methoxy-5-(2- ethylhexyloxy)-p-phenylenevinylene] (PFMEH-PPV)
, and poly[N-ethylhexyl-3,6-carbazolevinylene-alt-2-methoxy-5-(2-ethylhexyo
xy)-p-phenylenevinylene] (PCMEH-PPV), have been synthesized through the wel
l-known Wittig polycondensation reaction. The synthesized polymers were com
pletely soluble in common organic solvents and exhibited good thermal stabi
lity up to 400 degrees C. They showed UV-vis absorbance and photoluminescen
ce (PL) in the ranges of 355-430 and 480-540 nm, respectively. The maximum
emission peaks of dialkoxy-substituted PCMEH-PPV and PFMEH-PPV appeared at
520 and 540 nm, respectively, which were both blue-shifted about 55-75 nm c
ompared to that of MEH-PPV. Especially, PCBTS-PPV and PFBTS-PPV showed much
more blue-shifted emission maximum peaks at 480 and 495 nm corresponding t
o the blue and greenish-blue lights, respectively. Although PCBTS-PPV and P
FBTS-PPV consist of conjugated segments without any kinked linkages, they s
howed far more blue-shifted emissions compared with other PPV related copol
ymers due to little electron-donating effect of the silyl substituent. More
over, PFBTS-PPV and PCBTS-PPV showed extremely high PL efficiencies. Surpri
singly, the PLeff (Phi = 0.81) of PFBTS-PPV is one of the highest values am
ong the currently reported solid film PLeff of PPV derivatives. The single-
layer light-emitting diode was fabricated in the configuration of ITO (indi
um-tin oxide)/polymer/Al. Electroluminescence (EL) maxima of PCBTS-PPV and
PFBTS-PPV were shown at 480 and 500 nm, respectively, each corresponding to
the blue and greenish-blue emission. The measurement of current vs electri
c field strength showed the threshold biases of PCBTS-PPV and PFBTS-PPV to
be about 1.8 x 10(8) and 1.2 x 10(8) V/m, and PCBTS-PPV and PFBTS-PPV showe
d 13 and 32 times higher relative EL quantum efficiencies compared to that
of MEH-PPV.