Computation of molecular emission

Introduction

The Emission module computes transition dipoles, either fluorescent (one transition dipole) or phosphorescent (three transition dipoles, also called second order moments (SOM)) in organic molecules, to help understand in which direction or plane a molecule emmits light, and optionally to later analyze the orientation of the transition dipoles in thin films generated with Deposit to estimate outcoupling efficiency. For such an analysis on a Deposit morphology, the transition dipole vectors are tranformed into an internal molecular basis (see below). A full description of the analysis if Ir-based emitters in CBP can be found here and here.

WaNo

WaNo for fluorescent emission, Orientation Analysis Output disabled WaNo for phosphorescent emission, Orientation Analysis Output enabled

Input files and parameters

General settings

  • Molecule: Load a file containing the structure of a single molecule in either xyz, pdb, cml or mol2 format
  • Optimize Geometry: Optimize the geometry into the ground state using DFT as implemented in Turbomole. If enabled, you can set functional and basis set. We recommend to use def2-SVP and B3LYP. If you use molecule.pdb from a respective Parametrizer run (with geometry optimization enabled) as input, leave this option unchecked.
  • Emission type: Chose if you want to analyze fluorescent or phosphorescent emission moments of the molecule

Fluorescent Calculation Options:

In this box you can set basis and functional for your TD-DFT computation (computations are performed with Turbomole), as well as the multiplicity (Singlet or Triplet) and the number of excitations you are interested in. We recommend to use def2-SVP and M06-2x.

Phosphorescent Calculation Options:

Phosphorescent properties of molecules are computed using the Dalton engine. Again we recommend to use def2-SVP as basis. Only B3LYP is available as functional. Note that automatically, a different ECP basis is assigned to heavy atoms ("Rb", "Sr", "Y", "Zr", "Nb", "Mo", "Tc", "Ru", "Rh", "Pd", "Ag", "Cd", "In", "Sn", "Sb", "Te", "I", "Cs", "Ba", "La", "Ce", "Pr","Nd", "Pm", "Sm", "Eu", "Gd", "Tb", "Dy", "Ho", "Er", "Tm", "Yb", "Lu", "Hf", "Ta", "W", "Re", "Os", "Ir", "Pt", "Au", "Hg", "Tl", "Pb", "Bi", "Po") to account for spin-orbit coupling.

Output for Orientation Analysis

If you wish to analyze the orientation of transition dipoles of emitter molecules, e.g. embedded in different host materials, in a Deposit morphology, enable this option. The Emission module will then generate a yml file that contains information of the relative orientation of the transition dipole within the molecule. To this purpose, each transition moment is expressed in an internal basis that is defined by vectors between a center atom and three other atoms. If the option "Orientation Analysis Output" is checked, you can therefore adapt the following settings:

  • Automatic Center Atom: If checked, the atom closest to the center of geometry of the molecule will be set as center atom, i.e. the atom from which the (linearly independent) unit vectors of the internal coordinate system origin and point to three different atoms in the molecule. If unchecked, you can set this ID manually.
  • Atom 1, 2, 3: Set the IDs of three additional atoms in the molecule, such that the three vectors between core atom and each of the Atom 1, 2 and 3 are linearly independent.

If you are unsure, which atom IDs to provide, you can vizualize the molecule, e.g. with Jmol, pymol or VMD, and identify a center atom and three additional atoms to generate three linearly independent vectors. Make sure that no ID is used twice and note that in the Emission module, we start the count at ID 0, whereas some programs for vizalization may start to count at ID 1.

Output files

Visualiztion of transition moments

Vizualization of transition moments

The emission module generates files to vizualize the transition moments as well as the static dipole in the molecule using VMD. These files can be found in the "vmd_output" folder in the runtime directory. Enter the following command line in a terminal:

vmd molecule.xyz -e dipole_and_phosphorescence.tcl

This will visualize your molecule along with static dipole (red arrow) and transition moments (orange arrows) as illustrated for Ir(bppo)2(acac) to the right.

Output for orientation analysis in a Deposit morphology

The file "orientation_analysis_input.yml" is a dictionary containing information of transition dipoles expressed in the interal basis as defined using the atom IDs above. You can load this file into the Orientation Analysis module along with a morphology from Deposit (see tutorials here and here). Further, the norm of the static dipole is printed in this file.

Radiative lifetimes

As of now, radiative lifetimes need to be extracted from the raw runtime data. We will provide an update shortly to include radiative lifetimes in the main output of the Emission module.

  • Phosphorent lifetime: Check for lines containing "Total phosphorescence lifetime" in the file "calculations/quadratic_response/input_geometry.out" in the runtime folder of your run
  • Fluorescent lifetime: Coming soon!

 

 

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