Synthesis and Optical Properties of Acrylic Copolymers Containing AlQ3Pendant Group for Organic Light Emitting Diodes

Abstract

펜던트기가 tris(8-hydroxyquinoline) aluminum (<TEX>$AlQ_3$</TEX>)으로 된 아크릴 단량체(HEMA-p-<TEX>$AlQ_3$</TEX>) (HEMA = 2-hydroxyethyl methacrylate)를 각각 메틸메타크릴레이트(MMA), 아크릴로니트릴(AN), 순수 HEMA와 공중합하여 3가지 아크릴 공중합체[MMA-co-HEMA-p-<TEX>$AlQ_3$</TEX> (공중합체 1), AN-co-HEMA-p-<TEX>$AlQ_3$</TEX> (공중합체 2), HEMA-co-HEMA-p-<TEX>$AlQ_3$</TEX> (공중합체 3)]를 라디칼 공중합법으로 합성하였다. 25 wt%의 HEMA-p-<TEX>$AlQ_3$</TEX>를 함유한 공중합체 1,2,3의 유리전이온도(<TEX>$T_g$</TEX>)는 각각 158, 150, <TEX>$126^{\circ}C$</TEX>로 나타났으며, 이는 유기발광다이오드(organic light emitting diodes, OLED)로써 지녀야 하는 우수한 열 안정성을 만족하였다. 그리고 이들 공중합체는 테트라하이드로퓨린, 디메틸포름아미드, 톨루엔 및 클로로포름 등과 같은 용매에 잘 용해되었으며, 자외선-가시광선의 흡수 및 발광 거동이 순수 <TEX>$AlQ_3$</TEX>와 거의 동일함을 알 수 있었다. 또한 이들 공중합체를 스핀 코팅하여 녹색의 OLED 디바이스를 제조한 후 전류 밀도-전압 곡선을 비교하였다. 공중합체 3을 사용한 OLED 디바이스의 on-set 전압은 약 2 볼트로써 다른 두 공중합체 OLED 디바이스의 전압(공중합체 1: 약 3 볼트, 공중합체 2: 약 4 볼트) 보다 낮음을 알 수 있었다. Three acrylic copolymers containing tris(8-hydroxyquinoline) aluminum (AlQ3) pendant group (25 wt%), acrylateco-HEMA-<TEX>$AlQ_3$</TEX> (25 wt%), were successfully synthesized by free radical polymerization from acrylates [methyl methacrylate (MMA), acrylonitrile (AN) or 2-hydroxyethyl methacrylate (HEMA)] with HEMA functionalized with AlQ3 pendant groups (HEMA-p-<TEX>$AlQ_3$</TEX>). The glass transition temperatures (<TEX>$T_g$</TEX>) of MMA-co-HEMA-p-<TEX>$AlQ_3$</TEX> (copolymer 1), AN-co-HEMA-p-<TEX>$AlQ_3$</TEX> (copolymer 2) and HEMA-co-HEMA-p-<TEX>$AlQ_3$</TEX> (copolymer 3) were found to be 158, 150 and <TEX>$126^{\circ}C$</TEX>, respectively. They have good thermal stability: a very desirable feature for the stability of OLEDs. Their solubility, thermal properties, UV-visible absorption and photoluminescence behaviors were investigated. They were found to be soluble in various organic solvents such as tetrahydrofuran (THF), dimethylformamide (DMF), toluene and chloroform. It was also found that the UV-visible absorption and photoluminescence behaviors of these copolymers were similar to those of pristine <TEX>$AlQ_3$</TEX>. Green organic light-emitting diodes (OLEDs) have also been fabricated using these copolymers as light emission/electron transport components obtained easily by spin coating, and their current density voltage (J-V) curves were compared. The OLED device of the copolymer 3 had the lowest turn-on voltage of about 2 V compared to other copolymer types devices.