Synthesis and Optoelectronic Properties of Conjugated Polymers Containing Benzo[c]cinnoline Moieties

• Main Authors: Hsin_Chung Wu, 吳信忠
• Other Authors: Jyh-Chien Chen
• Format: Others
• Language: en_US
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/m55hdd

博士 === 國立臺灣科技大學 === 材料科學與工程系 === 104 === The conjugated polymers, including poly(1,3,4-oxadiazole)s (POXD (I) and (T)), poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]s (MEH-PPVs) (P10, P25, and P50), and polyfluorenes (BF10, BF25, and BF50) containing benzo[c]cinnoline moieties, were synthesized and characterized. The polyfluorene containing benzo[c]cinnoline moieties, BF50, was further quaternized to obtain the polyelectrolyte, BF50Br. Two reduction peaks were observed for POXD (I) and (T) during cyclic voltammetry (CV) cathodic scan. From CV characterization combined with the results from molecular simulation, we concluded that the first reduction occurred at oxadiazole moiety and benzo[c]cinnoline moiety was responsible for the second reduction. It indicates that oxadiazole has stronger electron affinity than benzo[c]cinnoline. The bottom-gate, top-contact organic field-effect transistors (OFETs) based on P10, P25, and P50 were performed under ambient conditions. The OFET based on P10 only exhibited p-channel characteristic. In contrast, we could not determine the hole mobilities of P25 and P50. The OFETs of these two polymers only exhibited n-channel characteristics. No significant variation in electron mobility can be observed after P50-based OFET was stored under ambient conditions up to 30 days. To the best of our knowledge, this is the first time that air-stable n-channel MEH-PPV derivatives have ever been reported. It indicated that p-type MEH-PPV can be transformed into n-type materials upon incorporation of benzo[c]cinnoline moieties. By UV irradiation (352 nm), the PL (photoluminescence) intensity of dilute polymer solutions of BF10, BF25, and BF50 was enhanced. The PL emission enhancement was attributed to the shorter conjugated length and the reduced donor-acceptor interaction caused by oxygen-containing groups that were formed on fluorene moieties by UV irradiation. The enhanced emission could be quenched further by the addition of proton donors such as trifluoroacetic acid. The completely alternating polymer BF50 consisting of fluorene and benzo[c]cinnoline moieties in dilute THF solution showed linear relationship between UV doses and PL quantum yields after UV irradiation. It exhibited good potential for UV-sensing applications. The solubility of the polyelectrolyte, BF50Br, in polar solvents including DMSO, NMP, methanol, and ethanol was improved obviously after modification. BF50Br exhibited blue-light emitting at 437 nm in NMP, accompanied with higher quantum yield and narrower FWHM (full width at half maximum) than its precursor polymer. The blue-light emission of BF50Br was also observed in DMSO, methanol, and ethanol. The unique optoelectronic properties have been investigated in a series of researches of various polymers containing benzo[c]cinnoline moieties.