4Organic luminescent materials are widely used in various consumer products such as highlighters, detergents .In addition to their use as chemical products, recen t development of organic materials from a new perspective has opened up a novel possibility for their use in optoelectronic devices . ex：display有機基板顯示器螢光筆zh.wikipedia.org
5In particular, the luminescence and unique semiconducting characteristics of organic materials can be combined, leading to the rapid development of organic semiconductor devices such as organic light emitting diodes (OLEDs)OLED電視LED可撓性OLEDzh.wikipedia.org
6OLEDs possess attractive features such as 1. high EL efficiency .ηEQE≈20%2. high contras t .OLED無論是顏色對比度或者是發光強度都比LCD來得好3. low weight and low cost .4. It possess the flexibleof charactertistic .cck1616tw.pixnet.net
8After extensive study of OLEDs for the past 20 years, electroluminescent(EL, 電致發光) materials have usually been classified by one of two mechanisms, fluorescence(螢光) or phosphorescence(磷光), where radiative decay occurs from singlet or triplet excited states, respectively .
11kr ：the fluorescence decay rate kp： the phosphorescence decay rate 電洞注入電子注入三重態激子τ ＝ 10-6~101 s單重態激子τ ＝ 10-9~10-8 s螢光τ ＝ 10-6~101 s磷光kr ：the fluorescence decay ratekp： the phosphorescence decay rateknp： the nonradiative decay rate from the T1 excited statekISC ：the intersystem crossing rate
12Photoluminescent(PL, 光致發光)： Photoluminescent materials have usually been classified by one of two mechanisms, fluorescence or phosphorescence , where radiative decay occurs from singlet or triplet excited states, respectively .光致發光IntersystemcrossingS1T1螢光磷光S1S0T1S0
14kr ：the fluorescence decay rate kp： the phosphorescence decay rate 受光激發螢光磷光τ ＝ 10-6~101 sτ ＝ 10-9~10-8 skr ：the fluorescence decay ratekp： the phosphorescence decay rateknp： the nonradiative decay rate from the T1 excited statekISC ：the intersystem crossing rate
15螢光和磷光最大的不同就是輻射生命期的長短： 螢光輻射生命期：10-9~10-8 s 磷光輻射生命期：10-6~101 s 奎寧水因吸收紫外光之後而放出螢光夜明珠所放出的磷光zh.wikipedia.org/zh-tw
16spin-orbit coupling → <L · S>＝value The use of phosphorescent iridium 銥(Ir) complexes overcame the limitation of exciton production efficiency through spin-orbit coupling, resulting in devices with very high external EL efficiency (EQE)of over 20% . In fact, the high EQE of such phosphorescent complexes prompted commercialization of OLEDs.Unfortunately, rare metals such as Ir and Pt are not the ideal choice for OLED emitters. They are unevenly distributed resources, expensive, rather low solubility and produce toxic waste .spin-orbit coupling → <L · S>＝value<L · S>的值越大，就越有可能放出磷光iridium 銥(Ir) complexes
17To produce OLED emitters without these drawbacks, we recently prepared novel light-emitting materials that realize high efficiency without using rare metal complexes by taking advantage of very efficient thermally activated delayed fluorescence (TADF) .
19Although some molecules are already known to exhibit TADF, their efficiencies are generally quite low .In the last few years, they have surveyed various candidates as TADF emitters and found the molecules that exhibit significant TADF .
20SnF2OEPCC2TAΔEST ＝0.24eVΔEST ＝0.06eVηEQE ＝0.1%ηEQE ＝11%PIC-TRZACRFLCNΔEST ＝0.1eVηEQE ＝5.3%>2%ΔEST ＝0.1eVηEQE ＝10%considering only the photoluminescence (PL) efficiency of ΦPL ＝39% related toconventional fluorescenceJ. Chem. Theory Comput. 2013, 9, 3872−3877
21An OLED containing this molecule exhibited a high ηEQE of 14% ±1% Recently, they found an advanced molecule with an ultimately small ΔEST ≈ 0eV, virtually zero gap. They believe that this is the first report on the molecules having zero-gap between the singlet and triplet excited states.An OLED containing this molecule exhibited a high ηEQE of 14% ±1%S1△E≈0 eVT1S0
22In their successive design of TADF molecules, taking advantage of the backbone of PIC-TRZ, they systematically changed the number and position of an indolocarbazole unit through quantum mechanism calculation .Indolocarbazole unitPIC-TRZPIC-TRZ2
24計算方法：DFT/PBE0/6-31G(d) DFT(Density Function Theoy) PBE0： 氫原子的分子軌域Setting up of parameter duringcalculation6-31G(d) ：A kind of basis setΦi ： electron basis functionci ： coefficientΨ：the molecular orbital of wavefunction
25PIC-TRZ HOMO LUMO HOMO and LUMO are separated incompletely ΔEcalc＝0.08eVHOMOLUMOPIC-TRZ2HOMO and LUMO are completely separatedΔEcalc＝0.003eV
26Their goal is to achieve high TADF performance in a solid film, aimed for application in OLEDs, so they focused on host-guest systems .Dope(摻雜)hostguestPIC-TRZ2
27Figures 3(a) and 3(b) show transient PL decay and fluorescence (black line) and delayed fluorescence , 延遲螢光(red line) spectra of 6 wt %-PIC-TRZ2 doped(摻雜) into a 1,3-bis(carbazol-9-yl)benzene (mCP) host layer at T = 5K.λ ＝475nm(S1 ＝2.61 eV)Spectra corresponded well with each other, indicate that the delayed component is caused by TADF .
29no such emission spectrum was observed for PIC-TRZ2. In the case of PIC-TRZ, although we clearly observed the appearance of phosphorescence at low temperature, demonstrating a characteristic emission spectrum with clear vibrational peaks ,no such emission spectrum was observed for PIC-TRZ2.有磷光產生at T = 5K沒有磷光產生
30They conclude that the delayed component is related to TADF, and up-conversion occurs in PIC-TRZ2 even at T ＝ 5K, indicating it possesses virtually zero gap .
31The transient PL decay characteristics of PIC-TRZ2 at T＝300 K at Figure (c) Fast PL transient lifetimeτf ＝83 nsslow PL decay τd ＝2.7 μsiridium 2-phenylpyridineThey note that the latterτd is comparable to that of conventional Ir complexes such as iridium 2-phenylpyridine [Ir(ppy)3] derivatives with τ＝1~5 μs , indicating that PIC-TRZ2 has comparable transient performance of delayed fluorescence to those of Ir complexes .
32They measured the temperature dependence of the radiative decay rate of the delayed fluorescence(kr(TADF))＊阿瑞尼士方程式(Arrhenius equation)告訴我們：溫度越高，kr的反應速率就越快 !
33To maximize the TADF efficiency of films doped with PIC-TRZ2, they optimized the host materials.
35Triplet energy (eV) ΦPL TPT12.3318~24%TAPC2.8758~62%PYD22.9043~47%mCP2.9139~43%DPEPO≈3.149~53%UGH2≈3.557~61%學者猜測三重激子會在TAPAC分子待上一段很長的時間，而後再將能量釋放出來，並轉移至PIC-TRZ，使得PIC-TRZ的激子數增多，放光效率因而提升。Back energy transferenergy transferPIC-TRZ2
36Transient PL measurements revealed that Triplet excitation energy ：host materials ＞PIC-TRZ2Energy transferhost materialsPIC-TRZ2→ 延遲螢光會發生Triplet excitation energy ：host materials ＜PIC-TRZ2Energy transferhost materialsPIC-TRZ2→ 能量會以非輻射(nonradiation)的方式流失，例如：熱 。因而造成不必要的能量浪費。當然!這是我們不希望的!!!
37if energy transfer occurs readily, we can expect a further enhancement of EQE, suggesting a theoretical maximum of 11.8%.They tried to optimize the device parameters to maximize ηEQEdue to imperfect triplet exciton confinement.
38LiF/Al Cathode LiF/Al Cathode LiF/Al Cathode device V device VI device VIILiF/Al CathodeLiF/Al CathodeLiF/Al Cathode(45nm)TmPyPBiDPEPOTPBi(20nm)PYD2：6wt％PIC-TRZ2PYD2：6wt％PIC-TRZ2PYD2：6wt％PIC-TRZ2TAPACTAPACTAPAC(40nm)ITO AnodeITO AnodeITO AnodeMetal CathodeElectron Transport LayerLight Emitting PolymerHole Transport LayerITO Anode
41Summary ：1. They expect that improved understanding of molecular structures will reveal undeveloped functions that will further enhance OLED performance.2. While PIC-TRZ2 has nearly zero-gap energy, a rather high f of 60% was obtained. This is because PIC-TRZ2 has appreciable oscillator strength (振子強度) → <S0∣u∣S1> , leading to highly efficient TADF.＊振子強度的數值越大，兩個State之間的躍遷就越容易發生3. The radiative decay rate of the delayed fluorescence(kr(TADF))dependence of temperature .