Electroluminescent and Chemosensory Materials Containing Crown Ether: Molecular Design, Synthesis and Application

• Main Authors: Juin-MengYu, 游俊盟
• Other Authors: Yun Chen
• Format: Others
• Language: en_US
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/40696859590474912212

博士 === 國立成功大學 === 化學工程學系碩博士班 === 98 === Electroluminescent (EL) polymers have attracted considerable attention among scientists due to their potential applications as emitting layer in flat-panel displays. Polyfluorene (PFs) are widely applied in blue light-emitting material due to its high photoluminescence (PL), good chemical and thermal stability and high quantum yield. Moreover, various polyfluorene derivatives have been synthesized and applied not only in PLED but also in chemosensor. Interest in chemosensors is mainly attributed to their ability to produce signal gain in response to interactions with analytes. In this study, we attempted to design and synthesize novel electroluminescent and chemosensory materials. We choose crown ether as recognition moiety due to the natural characteristic of forming complex with cations. Combination of crown ether receptor with conjugated polymer backbone renders amplified fluorescence and absorption spectral variations in the presence of different metal ions. In chapter 4 and 5, a copolyfluorene (PFC) containing pendant crown ether as receptor was synthesized to investigate its recognition ability to metal cations. The PL response of PFC demonstrated high selectivity toward Ru3+ and Fe3+ ions. The PFC shows high sensitivity for Ru3+ with detecting limit as low as 1 ppm. Unexpectedly, the PFC was an efficient emitter for electroluminescent device as well. Double-layer electroluminescent device using PFC as emitting layer revealed maximum luminance (7910 cd/m2) and maximum luminance efficiency (2.3 cd/A) superior to those of poly(9,9-dioctylfluorene) (PF) device (860 cd/m2, 0.29 cd/A). Moreover, inserting a PFC layer between the PF emitting layer and calcium cathode led to reduced turn-on voltage (4.1 V), much lower than 7.1 V and 6.6 V of the double-layer PFC and PF devices, and enhanced device performance (2800 cd/m2 and 0.53 cd/A). To enhance sensitivity of the crown chemosensor, we synthesized a new chemosensory monoaza-15-crown-5 (CN-azacrown.) with electron-withdrawing cyano group to promote intramolecular charge transfer (ICT) process. To study the effect of electron-withdrawing group upon sensory characteristics of fluorescent chemosensors, a stilbene derivative H-azacrown. without electron-withdrawing group was also synthesized to compare its selectivity and sensitivity toward metal ions with CN-azacrown. (chapter 6). The sensitivity of CN-azacrown. toward Li+ is about one order higher than that of H-azacrown.. Clearly, e-withdrawing cyano group promotes ICT process in CN-azacrown. that leads to enhanced selectivity and sensitivity. Hyperbranched conjugated polymers usually show better sensing efficiency than linear counterparts. This has been attributed to that hyperbranched conjugated polymers provide greater number of possible exciton migration pathways through branch units, which increase the probability of exciton quenched by analyte. Furthermore, hyperbranched structure suppresses undesirable excimer/aggregate formation and improves film morphology, in which are beneficial to enhance PLED device performance. We synthesized a new trivinylfluorene monomer (M2) as branched unit to obtain hyperbranched polymer (HOFC) via Heck reaction to discuss the effects of hyperbranched structure on sensory characteristics and EL device performance (chapter 7). The corresponding analogous linear polymer (LOFC) was also synthesized for comparsion. The Stern-Volmer coefficient (Ksv) of HOFC toward Ru3+ ion is higher than LOFC slightly, which might be attributed to reduced conjugation caused by the twist (41.6o) at 4-position of fluorene units. This twist is unfavorable to the migration of excitons through the branch unit. Accordingly, the sensing properties of HOFC and LOFC are comparable. Moreover, hyperbranched HOFC reveals homogeneous film morphology. Double-layer electroluminescent devices, using thermally cross-linked HFC or LFC as emitting layer, showed that the turn-on voltage, maximum luminance and maximum luminance efficiency of HFC device (4.1 V, 7132 cd/m2 and 1.3 cd/A) surpassed those of LFC device (6.2 V, 331 cd/m2, 0.22 cd/A). Further, we used trivinylfluorene to react with dibromotriphenylamine to synthesize thermally cross-linkable hyperbranched polymer (HTP and HTPOCH3) serving as hole-transporting layer (HTL) in chapter 8. The resulted polymers demonstrated high solvent-resistance after thermal curing. The performance of MEH-PPV device (maximum luminance: 9310 cd/m2, luminance efficiency: 0.26 cd/A) was effectively enhanced by inserting the thermally cross-linked HTP or HTPOCH3 as HTL (HTP: 12610 cd/m2, 0.32 cd/A; HTPOCH3: 14060 cd/m2, 0.33 cd/A). Combination of conjugated polyfluorene with crown ether gives rise to promising multi-functional polymers applicable in electroluminescent and chemosensory areas. The crown ether demostrats specifically recognizes metal ions with the conjugated backbone amplifying the signal produced by binding with the metal cations, leading to high sensitivity characteristics. The enhancement in PLED device performance can be attributed to polar characteristic of crown ether promote compatibility between emitting layer and cathode (Ca). To enhance sensitivity, we introduced electron-withdrawing group (CN) to facilitiate ICT process. This design concept can be applied to sketch new conjugated-based chemosensors. Furthermore, the novel branched monomer M2 was used to synthesize hole-transporting hyperbranched polymers. Their hole-transporting ability can be readily adjusted by replacing triphenylamine moiety with other hole-transporting groups.