Vibrational progression of an OLED phosphorescent emitter

NOTE that this example was made with a previous version of ADF. Since the technical defaults have changed in 2014, screenshots of the menu panels and the actual results will be different with the current ADF modeling suite.

Triplet harvesting in OLEDs by tranisition metal complexes increased 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 T1 and S0 state of Pt(4,6-dFppy)(acac) to determine the vibronic fine structure from the Franck-Condon factors. We compare with the experimental results from the Yersin group (Chem. Phys. Lett. 468 (2009) 46-51).
You can download the sample input files, which have been kindly provided with the figures by Mr. Mori (Ryoka).

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

  1. Optimize the lowest singlet state (S0) and calculate frequencies
  2. Optimize the lowest triplet state (T1) 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 two calculations for your own complexes.

1. Optimization + frequencies lowest singlet state (S0)

Start from the .adf file in the sample download files. You can run this straight away. You can also copy the coordinates and make a new input. An optimization with the BP functional, SR ZORA, and the DZP basis (defaults to TZP for Pt) and Good numerical quality should be a good choice for quality and efficiency. Since ADF2014, the GUI also has a Geometry Opt & Freqs preset, which allows you to easily set up the compound job.

2. Optimization of the lowest triplet state (T1)

Using the same DFT settings as for S0, change the Spin polarization to 2 (triplet) and tick the unrestricted box. Run a geometry optimization + frequency (or use the .adf file provided).
Inspect the bonding energy of this T1 state with respect to that of the S0 state. This should be about 2.5 eV, or 20,000 cm-1, in good agreement with the experimental result for the 0-0 state. For other phosphorescent emitters we typically find quite reasonable agreement using the DeltaSCF energies between T1 and S0

3. Calculation of the Franck-Condon Spectrum

With your T1 calculation still open in ADFInput:

In the Main menu options panel of ADFInput: Preset → Properties Only
Properties → Franck-Condon Spectrum
Reference State: select the TAPE21 file (.t21) from your S0 calculation
Quanta Reference State → 5
Quanta Current State → 0 (we will not look at 'hot states')
From → -10000
To → 0
Save As (give it a different name) and Run

You can have a look at the included output which will list the spectral intensity from -10000 to 0 (the 0-0 state) by taking into account the overlap of the vibronic wavefunction (Franck-Condon factors). You can visualize the spectrum with ADFspectra and Gaussian-broaden the lines to take into account thermal broadening, the result may look something like this.

Vibronic Fine Structure Pt OLED Emitter

Vibrational fine structure T1 emission Pt complex, ADF calculations compared to experiment. Picture courtesy of Mr. Kento Mori, Ryoka, with kind perusal of experimental results from Prof. Yersin.