浅谈Ir(ppy)₃ 磷光发射机制的理论

自从磷光材料被应用到OLED以来，基于磷光机制的有机发光器件研究快速发展，其中代表性的有红、绿、蓝单基色磷光器件和全磷光白色磷光器件。由于自旋禁阻的原因，磷光量子产率要比荧光低得多，因此通常采用重原子效应等方法来提高磷光量子产率。当引入重原子后，自旋轨道耦合作用加强，使禁阻的三重态向单重态的跃迁变为允许，分子停滞在三线态的时间大幅缩短，极大地提高了器件的内量子效率，常用的重金属原子有Ir、Pt、Re、Os、Cu等。

磷光材料一般应具备良好的光热稳定性、较大的分子吸光截面、较高的系间窜越能力、室温下有较高的磷光量子产率和较短的三线态寿命等特征。由于有机材料中磷光的绿光材料最容易获得，因而研究最早也是从磷光绿光OLED开始，其中Ir(ppy)₃是最具代表性的材料，被广泛地应用到磷光器件中。

磷光发射速率是发光机理研究中的重要参数，本文将以Ir(ppy)₃为例，使用BDF和MOMAP软件计算其磷光发射速率。首先需要通过BDF量化软件进行结构优化、频率计算和旋轨耦合计算，之后基于BDF的结构优化和频率计算结果文件、旋轨耦合计算结果文件使用MOMAP软件进行磷光辐射速率的计算。

首先使用量子化学计算软件BDF进行Ir(ppy)₃的基态S0和第一激发三重态T1的结构优化和频率计算。

准备Ir(ppy)₃分子结构的xyz文件如下：

61

Ir   -2.606160230000     -0.262817540000      0.032585640000

C    -3.837298770000      2.407777490000      0.243683290000

C    -1.553000180000      2.622608110000      0.521271830000

C    -3.991643180000      3.786525490000      0.422094600000

C    -4.929719550000      1.476909230000     -0.003856060000

C    -1.634158680000      3.988444110000      0.709067180000

H    -0.591261780000      2.126459120000      0.554253960000

C    -2.889293280000      4.581787990000      0.656041260000

H    -4.972006580000      4.231616950000      0.376099570000

C    -6.263398690000      1.888616610000     -0.076321100000

H    -0.744068550000      4.570116630000      0.889344200000

H    -2.999939670000      5.647195600000      0.795286530000

C    -5.623129880000     -0.778047400000     -0.424041550000

C    -7.264449980000      0.973962040000     -0.319493370000

H    -6.527094820000      2.928025340000      0.057085040000

C    -6.940359500000     -0.364034500000     -0.495248330000

H    -5.397358100000     -1.824987250000     -0.570011260000

H    -8.293855190000      1.298147200000     -0.375111620000

H    -7.723296650000     -1.084118350000     -0.689505650000

C    -2.780095460000     -2.271307610000     -0.073978550000

C    -2.962145630000     -2.905938610000      1.179649240000

C    -2.704720750000     -3.101798200000     -1.194651040000

C    -3.053849400000     -4.297470620000      1.273150410000

C    -3.052375550000     -2.037406190000      2.345262930000

C    -2.797310890000     -4.477732940000     -1.095358170000

H    -2.574810200000     -2.657655530000     -2.171485550000

C    -2.970830350000     -5.080470100000      0.142706420000

H    -3.190782260000     -4.777448690000      2.231582660000

C    -3.251325250000     -2.483356810000      3.656088400000

H    -2.735191030000     -5.089028800000     -1.985144810000

H    -3.042943740000     -6.155896270000      0.221114210000

C    -2.995026490000      0.148733040000      3.092507280000

C    -3.319187740000     -1.576319800000      4.692855730000

H    -3.353725050000     -3.536644150000      3.859562860000

C    -3.186631940000     -0.222801710000      4.408749290000

H    -2.888815760000      1.194668600000      2.833837140000

H    -3.472767910000     -1.912494740000      5.707724440000

H    -3.232610730000      0.522480480000      5.186904590000

N    -2.927015180000     -0.717593640000      2.090156960000

C     0.125501920000     -0.309636820000     -1.075330180000

C     0.242318970000     -0.710559210000      1.197687130000

C     1.518232510000     -0.401785790000     -1.166132500000

C    -0.762473880000     -0.044853840000     -2.198985150000

C     1.619464440000     -0.811598610000      1.179643800000

H    -0.298309850000     -0.828666640000      2.128258480000

C     2.270161400000     -0.653514600000     -0.037593100000

H     2.007628100000     -0.277927520000     -2.118201950000

C    -2.150460220000     -0.005742870000     -1.917121780000

C    -0.287950380000      0.157363030000     -3.497950870000

H     2.165728000000     -1.009392350000      2.088259610000

H     3.346017750000     -0.726918300000     -0.099292420000

C    -3.004998770000      0.237880450000     -2.994864780000

C    -1.165335710000      0.397865570000     -4.532504760000

H     0.771521710000      0.127613130000     -3.708268180000

C    -2.529020200000      0.436535570000     -4.277665910000

H    -4.071982740000      0.267717660000     -2.824596670000

H    -0.792761550000      0.552584980000     -5.535050450000

H    -3.220629300000      0.622039860000     -5.087916480000

N    -0.487689310000     -0.467248190000      0.117089220000

N    -2.608631830000      1.850704260000      0.298598520000

C    -4.578169480000      0.115167240000     -0.176155400000

打开Device studio，点击File-new project，命名为phosphorescence.hpf，将Ir(ppy)₃_s0.xyz拖入Project中，双击Ir(ppy)₃_s0.hzw。接下来进行Ir(ppy)₃基态S0的结构优化和频率计算。选中Simulator → BDF → BDF，在界面中设置参数。在Basic Settings界面中的Calculation Type选择Opt+Freq，方法选择PBE0泛函，基组在Basis中的All Electron类型中，选择Def2-SVP。Basic Settings界面中的其它参数使用推荐的默认值，不需要做修改。

在SCF Settings界面中，DFT Integral Grid选择Coarse，Convergence Threshold选择Tight。SCF Settings界面中的其它参数使用推荐的默认值，不需要做修改。

在OPT Settings界面中，Convergence Threshold选择Tight。OPT Settings界面中的其它参数使用推荐的默认值，不需要做修改。

Freq Settings界面中的参数使用推荐的默认值，不需要做修改。之后点击 Generate files 即可生成对应计算的输入文件。选中生成的bdf.inp文件，右击选择open with，打开该文件，如下所示：

$compass

Title

C33H24IrN3

Geometry

Ir -2.60616023 -0.26281754 0.03258564

C -3.83729877 2.40777749 0.24368329

C -1.55300018 2.62260811 0.52127183

C -3.99164318 3.78652549 0.42209460

C -4.92971955 1.47690923 -0.00385606

C -1.63415868 3.98844411 0.70906718

H -0.59126178 2.12645912 0.55425396

C -2.88929328 4.58178799 0.65604126

H -4.97200658 4.23161695 0.37609957

C -6.26339869 1.88861661 -0.07632110

H -0.74406855 4.57011663 0.88934420

H -2.99993967 5.64719560 0.79528653

C -5.62312988 -0.77804740 -0.42404155

C -7.26444998 0.97396204 -0.31949337

H -6.52709482 2.92802534 0.05708504

C -6.94035950 -0.36403450 -0.49524833

H -5.39735810 -1.82498725 -0.57001126

H -8.29385519 1.29814720 -0.37511162

H -7.72329665 -1.08411835 -0.68950565

C -2.78009546 -2.27130761 -0.07397855

C -2.96214563 -2.90593861 1.17964924

C -2.70472075 -3.10179820 -1.19465104

C -3.05384940 -4.29747062 1.27315041

C -3.05237555 -2.03740619 2.34526293

C -2.79731089 -4.47773294 -1.09535817

H -2.57481020 -2.65765553 -2.17148555

C -2.97083035 -5.08047010 0.14270642

H -3.19078226 -4.77744869 2.23158266

C -3.25132525 -2.48335681 3.65608840

H -2.73519103 -5.08902880 -1.98514481

H -3.04294374 -6.15589627 0.22111421

C -2.99502649 0.14873304 3.09250728

C -3.31918774 -1.57631980 4.69285573

H -3.35372505 -3.53664415 3.85956286

C -3.18663194 -0.22280171 4.40874929

H -2.88881576 1.19466860 2.83383714

H -3.47276791 -1.91249474 5.70772444

H -3.23261073 0.52248048 5.18690459

N -2.92701518 -0.71759364 2.09015696

C 0.12550192 -0.30963682 -1.07533018

C 0.24231897 -0.71055921 1.19768713

C 1.51823251 -0.40178579 -1.16613250

C -0.76247388 -0.04485384 -2.19898515

C 1.61946444 -0.81159861 1.17964380

H -0.29830985 -0.82866664 2.12825848

C 2.27016140 -0.65351460 -0.03759310

H 2.00762810 -0.27792752 -2.11820195

C -2.15046022 -0.00574287 -1.91712178

C -0.28795038 0.15736303 -3.49795087

H 2.16572800 -1.00939235 2.08825961

H 3.34601775 -0.72691830 -0.09929242

C -3.00499877 0.23788045 -2.99486478

C -1.16533571 0.39786557 -4.53250476

H 0.77152171 0.12761313 -3.70826818

C -2.52902020 0.43653557 -4.27766591

H -4.07198274 0.26771766 -2.82459667

H -0.79276155 0.55258498 -5.53505045

H -3.22062930 0.62203986 -5.08791648

N -0.48768931 -0.46724819 0.11708922

N -2.60863183 1.85070426 0.29859852

C -4.57816948 0.11516724 -0.17615540

End Geometry

Basis

Def2-SVP

Skeleton

Group

C(1)

$end

$bdfopt

Solver

1

MaxCycle

366

TolGrad

3.0E-5

TolStep

1.2E-4

IOpt

3

Hess

final

$end

$xuanyuan

Direct

$end

$scf

RKS

Charge

0

SpinMulti

1

DFT

PBE0

D3

Grid

Coarse

ThreshConv

1.0D-9  5.0D-7

MPEC+COSX

Molden

$end

$resp

Geom

$end

选中bdf.inp文件，右击选择Run，弹出如下服务器提交的界面：

点击Run提交作业。任务结束后bdf.out，bdf.out.tmp，bdf.scf.molden三个结果文件会出现在Project中。

选择bdf.out，右击show view，在Optimization对话框中，显示结构已经达到收敛标准。

在Frequency对话框中，检查频率，若不存在虚频证明结构已经优化到极小点。

选择bdf.out文件，右击open with containing folder打开所在文件夹，在bdf.out文件中查找‘converged in’，紧接着输出的‘Molecular Cartesian Coordinates (X,Y,Z) in Angstrom : ’下的结构即为优化好的Ir(ppy)₃的S0结构。

编辑：黄飞