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標題: | 利用密度泛函理論及光譜量測探討有機發光二極體其分子的放光機制 Experimental and Theoretical Studies on The Photophysical Properties of OLED Molecules |
作者: | Hsiao-An Pan 潘校安 |
指導教授: | 周必泰(Pi-Tai Chou) |
關鍵字: | 密度泛函理論,有機發光二極體,銥金屬錯合物,鋨金屬錯合物,激發態質子轉移, DFT,B3LYP,OLED,Ir complex,Os complex,ESIPT, |
出版年 : | 2012 |
學位: | 碩士 |
摘要: | 本篇論文主要是利用光譜分析以及理論計算的技術來針對各式的有機發光二極體(OLED)其發光主體的光物理探討。
於本篇論文的前兩章,分別是以銥、鋨等有機金屬錯合物為主軸,探討其在激發態的光物理特性。首章中,共有九個銥金屬錯合物,其本意為OLED的發光主體,但就其光譜量測的結果看來,其放光甚弱效率並不如預期。而從理論計算的角度切入,在此利用含時密度泛函理論(TDDFT)來對這一系列的分子做計算,計算結果發現這些錯合物,其第一三重態(T1 state)內皆含有中心金屬的d軌域躍遷,如此的三重態即可歸類為3MC dd 態(metal center dd transition state),而該能態因其位能曲面會與基態的位能曲面相互碰觸,產生一不放光的路徑,而此系列的分子便是遵循此路徑由激發態回到基態。 次章中,乃是鋨金屬錯合物,共有五種不同的衍生物。先從光譜量測上來看,這系列的分子多是放橘紅光,而隨著螯基的不同,放光效率也自65% 驟減至小於0.1%。在此,同樣也是利用計算的方式去探討為何有如此的差異?而就計算結果來論,首先,若將其螯基內的硫原子換做是氮原子並加上一碳鏈分支,如此該螯基的推電子效應便被提升,即螯基的pi*軌域能量被向上拉抬,同理,若將螯基內的共軛長度減少,也會使得pi*軌域能量被向上推升,而一旦pi*軌域能量被拉升,而金屬的dpi軌域能量不變,使得原本進行dpi到pi*的MLCT (metal to ligand charge transfer)躍遷其所需的能量也增多。倘若在上述兩者共同的影響下,pi*軌域能量被向上推的過高,以至於鄰近甚至高過中心金屬的dsigma*軌域能量,如此,分子受光激發後,本應是分布到3MLCT態,卻在3MC dd態也有了分布,如此使得放光趨弱。 於末章中,乃是以有機小分子,利用其會進行激發態質子轉移(Excited State Intramolecular Proton Transfer, ESIPT)的方式來做為OLED的發光主體。分子的修飾,意在減緩其ESIPT的速率,藉此可得到兩個波段的放光,再藉由修飾其共軛的長度,去調控放光的位置,便可得出一放純白光的分子。而從理論計算的觀點來看,將分子修飾上苯環,的確會導致ESIPT的能障產生,使得反應變慢,此即因分子照光激發後要進行ESIPT反應,勢必得要透過一個低能量的振動去啟動整個反應,若將分子掛上了數個苯環,便會使得分子振動較為不易進而產生能障。而以苯環作修飾,除了能減緩ESIPT的速率外,其數目的多寡也能調控其共軛的長度,影響放光的光色,一舉數得,如此便可得到一全可見光譜的放光,即白光的OLED。 The first chapter is synthesis of a series of Ir(III) complexes with phosphite (or phosphonite) tripodal dicyclometalates. And all the Ir(III) complexes, virtually no emission can be observed in either solution at room temperature or 77 K CH2Cl2 matrix. Time-dependent DFT calculation indicates that the lowest energy triplet manifold involves substantial amount of metal centered 3MC dd contribution. Due to its repulsive potential energy surface (PES) that touches the PES of ground state, the 3MC dd state executes predominant nonradiative deactivation process. The second chapter is preparation and characterization of a new class of emissive Os(II) complexes The resulting Os(II) complexes, except for 5 , all show bright emission spanning visible region from green to saturated red, and their structural versus spectroscopic properties have been comprehended by absorption/emission together with computational approaches. The result predicts the occurrence of dominant radiationless quenching process from the 3MC dd state, consistent with the lack of emission observed experimentally. As for complex 4 , due to the relatively small energy gap between 3MC dd and 3MLCT/pipi∗ states, thermal population (from 3MLCT/pipi∗ ) to the 3MC dd state is possible, giving the weak emission. The third chapter is using 7-hydroxy-1-indanone as a prototype(I), which exhibits excited-state intramolecular proton transfer (ESIPT), chemical modification has been performed by fusing benzene(II) and naphthalene rings(III), based on a provident balance between destruction of aromaticity and compensation of pi-conjugation. As a result, the white light generation is achieved with a single ESIPT system. And the emission character is also studied by theoretical computation. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/16203 |
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