Poly(p-phenylenevinylene)與Poly(phenyleneazomethine)共聚物之合成與光學性質—硫烷基側鏈與間位或對位結構

Abstract

本論文合成三個系列的共聚物，系列I：Poly[m(p)-phenylene(diacetonitrile)vinylene-co-2-methoxy-5-(2’-ethylhexylthio)-p-phenylene vinylene] (m-CC(CN)，p-CC(CN))；系列II：Poly[m(p)-phenyleneazomethine-co-2-methoxy-5-(2’-ethylhexylthio)-p-phenyleneazomethine] (m-CN，p-CN)；系列III： Poly[m(p)-phenylenevinylene-co-2-methoxy-5-(2’-ethylhexylthio)-p-phenylene vinylene] (m-CC，p-CC)；以上共聚物均可溶於一般有機溶劑。 meta-linkage copolymers的Tg比para-linkage copolymers低10 至310C；系列I , II, III的5% weight loss (TGA)均在344至3810C間。 meta-linkage造成的主鏈彎曲，使有效共軛長度下降，分子鏈間的aggregation及excimer現象減少，使得最大發光強度較強且波長(λmax)藍位移15至 49nm；另外，由於硫原子的體積大於氧，立體障礙造成有效共軛長度下降，使具有alkylthio側鏈的m-CC、p-CC、p-CN較文獻中具有alkyloxy側鏈的共聚物發光波長(λmax)藍位移8 至24nm；系列II (m-CN，p-CN)的共軛系統(-C=N-)具有拉電子能力，而系列I (m-CC(CN)，p-CC(CN)) 的共軛系統(-C=C(CN)-)也具有強拉電子基cyano group，發光波長(λmax)依序為：系列I (m-CC(CN)，p-CC(CN)) > 系列II (m-CN，p-CN) > 系列III (m-CC，p-CC)，但由於系列II共軛系統(-C=N-)氮上的孤對電子(lone pair electrons)造成苯環間的共平面程度下降，其發光強度小於系列I及系列III。 元件( ITO / PEDOT : PSS / m-CC(CN) / LiF / Al )的EL最大發光波長在590 nm，受限於元件壽命及設備不足，目前尚無法測得元件的其它數據。

Three copolymer systems were synthesized in this study, i.e. poly[m(p)-phenylene(diacetonitrile)vinylene-co-2-methoxy-5-(2’-ethyl hexylthio)-p-phenylenevinylene] [Series I : m-CC(CN), p-CC(CN)]; poly[m(p)-phenyleneazomethine-co-2-methoxy-5-(2’-ethylhexylthio)-p-phenyleneazomethine] [Series II : m-CN, p-CN]; poly[m(p)-phenylene vinylene-co-2-methoxy-5-(2’-ethylhexylthio)-p-phenylenevinylene] (Series III : m-CC, p-CC). All these copolymers were soluble in common organic solvents. All of Tg of meta-linkage copolymers were lower about 10 to 310C compared with those of para-linkage copolymers. The 5% weight loss temperature of copolymers were in the range of 344 to 3810C. The photoluminescence (PL) of meta-linkage copolymers indicated stronger in intensity but shorter ones in λmax compared with those of para-linkage copolymers because meta-linkage reduced effective conjugation length and formed aggregation or excimers between main chains of copolymers. In addition, the PL of the copolymers containing alkylthio side chains showed shorter λmax compared ones with containing alkyloxy side chains presumably because the sulfur atom increased steric hindrance. The maximum PL wavelength are in the order : Series I > Series II > Series III, because of the different electron withdrawing groups in conjugation system (Series I : cyano grop, Series II : -C=N-). However, the PL intensity of Series II were weaker than those of Series I and Series III, it could be due to the twist of the conjugation system in Series II (-C=N-). The device structure is ITO / PEDOT : PSS / m-CC(CN) / LiF / Al. It was drived at 9 V, and the emission maximum wavelength (λmax) in EL spectrum was observed at 570 nm.