電致發光半導體高分子之分子鏈構形與超分子結構之研究

A Study on the Global Chain Conformation and Supramolecular Structure of Electroluminescent Semiconducting Polymer

歐陽文忠(Wen-Chung Ou-Yang)

指導教授 ： 陳信龍

國立清華大學/工學院/化學工程學系/博士(2006年)

摘要

摘 要
夲研究探討溶劑、濃度及溫度對MEH-PPV 在溶液中的形態的影響。即便在極稀薄溶液中，MEH-PPV 分子鏈亦可能有聚集(aggregation)的現象，因為聚集，使有效共軛鏈長增長，因而造成PL 光譜紅位移；我們發現不管溶劑與分子量為何；當分子鏈數目濃度超過109/ml就會產生聚集，此暗示聚集與分子鏈的數目有最直接之關係。在更稀薄分子鏈數目<109/ml的濃度時，MEH-PPV 並無聚集的現象，此時螢光放射强度，與分子量成正比，表示該強度與發光高分子粒子的體積大小有關。
溶液濃度增濃時，螢光放射粒子的數目增加，會使放射強度增強，但發光粒子的數目持續增加，遮蔽(shield)效應亦開始顯現，故螢光總放射強度受到此一加一減之影響。
我們亦探討溶劑性質對MEH-PPV 聚集之影響，含苯環芳香族的溶劑，例如甲苯，較不含苯環的脂肪族溶劑THF 而言，不易誘導主鏈的聚集，此時有較多側鏈醚基產生的聚集(不管是分子鏈內或是分子鏈間)，當提升溶液的溫度，增加動能，能輕易使之解聚集；反之，在
THF 溶液中，有比較多的主鏈聚集，因此聚集體相當堅牢，不易藉由提升溫度而使之解聚集。
我們進一步利用小角度中子散射(SANS)解析MEH-PPV 於甲苯中的聚集行為，發現濃度在遠低於液向型液晶的門檻濃度時，MEH-PPV 分子鏈就有聚集發生，此聚集產生奈米尺度的盤狀區域(domain)，從溫度之依存性，我們進一步推測，這些聚集區域呈現微胞物性，與完全溶解的鏈段共存。在SANS 研究的濃度範圍(0.1~1.0 wt％)，我們提出聚集的根源，與桿狀分子片段的連結性(connectivity)及雙親性(amphiphilicility)有關。值得注意的是，當增加高分子的濃度時，此種盤狀聚集區域，可能作為巨觀向列液晶相之核種。
從夲研究中，我們可以得知不同聚集的形態結構，可以改變MEH-PPV 的有效共軛鏈長，
可以使其放射不同的光色，因而在應用上，可以調變其光物理性質，進而改變元件的發光效
率。

關鍵字

電致發光 ； 半導體高分子 ； 分子鏈構形 ； MEH-PPV ； 小角度中子散射 ； 聚集

並列摘要

Abstract
In this research, the effects of the solvent nature, concentration of solution and temperature which affect the morphology of MEH-PPV polymer chains in solution state
were inquired. We discover, in spite of solvent nature and the molecular weight of MEH-PPV, the existence of aggregation phenomenon even in ultra dilute solution as the
amount of molecular chains of MEH-PPV larger than 109/ml, it implicates aggregations could be a colligative property which depends only on the number of solute molecular
chains. Because molecular chains’ self-assembling make the effective conjugated length increasing, therefore results in photoluminescence (PL) spectrum red shift, it implicates the aggregation has a lot of significant meaning in photophysical properties. We also discover, below the aggregated concentration region, the intensity of photoluminescence increases as the solute molecular weight increases, it implicates the intensity of photoluminescence
depends on the size of luminescence particles.
The affinity of solvent nature to the side chain and backbone of MEH-PPV decides the type and degree of aggregation of solvent molecular chains. Aromatic solvents such as toluene and chlorobenzene have good affinity to the backbone of MEH-PPV, so the main chains’ aggregation were forbidden attributed to the aromatic solvent filling up among the main chains, but allow the side chains’ aggregation. On the contrast, aliphatic solvents such
as chloroform and tetrahydrofuran (THF), THF especially, have good affinity to the side chain of MEH-PPV, so the main chains’ aggregation proceed in the way of adamant
zipper-like aggregation as the concentration of solution was increased, which could not be capable deaggregated by means of the heating process.
Although when MEH-PPV was dissolved in toluene we have learned from our
temperature-dependent SANS experiments which exhibits the good thermal reversibility, as heating the aggregated cluster deaggregate and as cooling the deaggregated segments
aggregate again, but not include THF system due to entirely different aggregation structure.

並列關鍵字

Electroluminescent Semiconducting Polymer ； Chain Conformation ； MEH-PPV ； SANS ； Aggregation