Vibrational progression of an OLED phosphorescent emitter
*********************************************************

ADF Spectroscopy UV/Vis Organic electronics OLEDs Vertical absorption
Phosphorescence Franck-Condon spectrum

Triplet harvesting in OLEDs by transition metal complexes increases
the maximum efficiency from 25% to 100%. Singlet excitons are rapidly
converted to triplet excited states and fast phosphorescence can be
achieved by strong spin-orbit coupling. In this example we calculate
the frequencies of the T_1 and S_0 state of Pt(4,6-dFppy)(acac) in the
gas phase to determine the vibronic fine structure from the Franck-
Condon factors. We compare these with the experimental results from
the Yersin group, who studied Pt(4,6-dFppy)(acac) in n-octane. [1] The
sample command line input files can be downloaded "here".

To calculate the overlap of the vibronic wave functions, we first need
to calculate the frequencies of the two electronic states involved,
followed by the Franck-Condon calculation. So we have three steps:

1. Optimize the lowest singlet state (S_0) and calculate frequencies

2. Optimize the lowest triplet state (T_1) and calculate frequencies

3. Calculation of the Franck-Condon Spectrum

You can start straight away with the "example input"  files or read
further to learn how to set up these three calculations in the GUI for
your own complexes.


1. Optimize lowest singlet state (S_0)
======================================

First, the geometry of the complex (in its lowest singlet state) must
be optimized by performing the following steps. (Another basis set and
functional can be used as well.)

Remark: Pt(4,6-dFppy)(acac) has C_s-symmetry. The use of symmetry may
speed up the calculation and may improve the analysis of the results.

   **1.** **SCM** → **New Input**
   **2.** In AMSinput make the complex by copying the "xyz coordinates"
   **3.** Click the Symmetrize button [image: SymmTool][image]
   **4.** Select the Task **Geometry Optimization**
   **5.** Tick the **Frequencies** box
   **6.** Set the **XC functional** to **GGA:BP86**
   **7.** Set the **Basis Set** to **TZP**
   **8.** Set the **Frozen core** to **Small** and the **Numerical quality** to **Good**
   **9.** Run the calculation (**File** → **Run**)
 [image]


2. Optimize lowest triplet state (T_1)
======================================

For calculating the complex in its T_1 state, the same DFT settings
should be applied as for S_0, but an unrestricted calculation needs to
be performed.

Remark: An open shell electronic configuration may break symmetry. In
this case Pt(4,6-dFppy)(acac) also has C_s-symmetry in the lowest
triplet state, as one may check if one looks at the results of the
frequency calculation. In general, however, one may have to break
symmetry in the starting geometry, in order to get a non-symmetric
optimized geometry.

   **1.** **SCM** → **New Input**
   **2.** In AMSinput make the complex by copying the "xyz coordinates"
   **3.** Click the Symmetrize button [image: SymmTool][image]
   **4.** Select the Task **Geometry Optimization**
   **5.** Tick the **Frequencies** box
   **6.** Tick the **Unrestricted** box
   **7.** Change the **Spin Polarization** to "2"
   **8.** Set the **XC functional** to **GGA:BP86**
   **9.** Set the **Basis Set** to **TZP**
   **10.** Set the **Frozen core** to **Small** and the **Numerical quality** to **Good**
   **11.** Run the calculation
 [image]

   The energy of the T_1 state can be found at the bottom of the logfile or in the output
   The difference in energy of the  T_1 state with respect to the  S_0 state can be calculated now

This difference in energy should be about 2.5 eV which is in
reasonable agreement with the experimental result for the 0-0
transition, which is 21461 cm-1 (2.66 eV) for Pt(4,6-dFppy)(acac) in
n-octane. [1].


3. Calculation of the Franck-Condon Spectrum
============================================

Next the Franck-Condon spectrum will be calculated. Important is to
make a new AMSinput file. In this example we calculate the vibrational
resolved spectrum for emission from the T_1 state to the S_0 ground
state. We do not consider vibrational excitations in the T_1 state
(i.e. "hot states"). Thus the reference state is the vibrational
ground state of the electronically excited T_1 state.

   **1.** **SCM** → **New Input**
   **2.** On the main panel choose **Properties Only** as the **Task**
   **3.** Make sure that the **Frequencies** box is ticked
   **4.** In the panel bar, select **Details** → **Files (Restart)**
   **5.** Choose in **Properties only for** the results folder of the S_0 calculation (for instance "S0_GeoFreq.results")
   **6.** In the panel bar, select **Properties** → **Franck-Condon Spectrum**
   **7.** Tick the **Calculate Franck-Condon spectrum** box
   **8.** Select as the **Reference state** the "adf.rkf" file from the T_1 calculation (e.g. in the "T1_GeoFreq.results" folder)
   **9.** Select **Type → Emission**
   **10.** Run the calculation
 [image]

More information about the calculation of Franck-Condon spectra can be
found in the AH-FC: Adiabatic Hessian Franck-Condon section.

The output will list the spectral intensity from -95000 cm^-1 to 500
cm^-1 (relative to the 0-0 transition) by taking into account the
overlap of the vibronic wavefunction (Franck-Condon factors). The FCF
spectrum can be visualized at **SCM** → **Spectra**. The lines can be
Gaussian-broadened to take into account thermal broadening.

   **1.** **SCM** → **Spectra**
   **2.** **|Axis|** → **Flip Horizontal**
   **3.** Enter "300" for the **Width**
   **4.** Enter "21461" (experimental 0-0 transition) for the **Offset**
   **5.** Double-click on the x-axis to open the Graph options window
   **6.** Enter "17000" for Minimum value and "22500" for Maximum value
   **7.** Close with **OK** in Graph options window
 [image]


References
==========

[1] A. F. Rausch, M. E. Thompson, H. Yersin, *Triplet state relaxation
    processes of the OLED emitter Pt(4,6-dFppy)(acac)*, Chemical
    Physics Letters 468, 46 (2009)
