1. Mike Scudder
CHEM 7350
November 15, 2017

2. d6 Ru(II), Os(II) give long excited-state lifetimes, high luminescent efficiencies (increase likelihood of either an energy or electron-transfer process occurring prior to radiative/nonradiative relaxtion)
d6 Ir(III) exhibits longer lifetimes in solution due to heavier SOC

3. Cyclometalated iridium complexes
Ir emitters can harvest both the singlet and triplet electrically generated excitons.
Strong phosphorescence shown even at room temperature because the strong SOC increases radiative decay rate
Have generated intense interest due to excellent photophysical properties
Rational design and selection of the cyclometalating ligand and ancillary ligand provide an opportunity to control the photophysical, electrochemical, and steric properties

4. Cyclometalated iridium complexes
Dye-sensitized solar cells1
Absorption and emission spectra of (ppy)2Ir(acac)2
OLEDs
LECs
Current density (open squares) and luminance (triangles) vs time at 4V bias in an Ir(ppyPbu3)3:(PF6)33
Exhibit wide color tunability, high phosphorescence Φ
Photophysical, electrochemical properties crucial for materials performance

5. Controlling emission wavelength in Ir complexes
Ancillary ligands blueshift the absorption and emission energies by stabilizing HOMO, leaving LUMO unchanged
Destabilization of the 1MLCT state results in a decreased 1MLCT character in the lowest excited state, becomes more ligand-localized
Thompson et al. Inorganic Chemistry 2005 44 (6),

6. Controlling kr, knr in iridium complexes
Excited-state lifetimes and quantum yields are used to calculate kr, knr
kr: based on the amount of metal character in emitting excited state, energy gap between singlet and triplet states
knr: intramolecular vibronic coupling and thermal accessibility of metal-centered states
Thompson et al. Inorganic Chemistry 2005 44 (6),

7. Structural modifications of Ir complexes
Potential (V vs Fc+/Fc)
Current
“Dynamic Properties”
“Static Properties”
knr kr 3A
1A* 1A
ISC E
phosphorescence
hν-E
fluorescence hν
Both static and dynamic properties sensitive to complex architecture
Motivation: Find design approach to allow variation of kr , knr independently of redox potential and emission maximum

8. Synthetic Approach: Tris-heteroleptic complexes
Not emissive at room temp.
To date, only C^N ligands with the same chemical core but different substitution patterns have been used to prepare tris-heteroleptic complexes. Ppy=2-phenylpyridine. Ppz=1-phenylpyrazole.

9. Cyclic voltammetry results (complexes 1-10)
Eox (V)
0.43
0.73
0.58
Eox (V)
0.49
0.79
0.64
Eox (V)
0.45
0.75
0.61
0.60
CV: useful experimental techniques to estimate the energy levels of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of the ground state of Ir complexes
Pyridine-containing complexes: show quasi-reversible oxidation and reduction potentials
Adding Fluorines to substituent increases oxidation potential by removing electron density from Ir(III) center

10. Cyclic voltammetry results (isomers)
Eox (V)
0.73
0.72
0.76
Each diastereomer contains at least one pyridine group: quasi-reversible redox
Replacing acac with pic: shifts both potentials by 150 mV

11. UV-Vis results Ppz ligand: not emissive at room temperature
Direct population of 3A
LC 1ππ*
Ppz ligand: not emissive at room temperature
Replacing ppy with ppz has negligible effect on redox potentials, emission spectra
Significant impact on kr, knr
MLCT

12. UV-Vis results
Emission maxima dictated by the overall number of fluorine substituents on the complexes
Complex 5: Not emissive at room temperature

13. UV-Vis results
Placement of F on ligand: no effect on redox/emission maxima
Significant effect on kr, knr

14. UV-Vis results: tris-heteroleptic isomers
Unlike acac, pic is asymmetric and nonchromophoric
Resulted in blueshift relative to acac complexes
Isomers a and b: very similar absorption spectra
Close similarity confirmed by theory

15. Tris-heteroleptic isomers: density differences
Blue represents electron density, red represents hole density
First excited state of both isomer has MLCT character, large HOMO-LUMO contribution
T1: Combination of MLCT and LC character

16. Summary
A series of bis, tris-heteroleptic cyclometalated iridium (III) complexes synthesized.
Use of picolinate as ancillary ligand provided two pairs of diastereomers.
Absorption, emission wavelengths and redox properties: controlled by overall structure of complexes.
Radiative, non-radiative constants: controlled by specific placement of substituents.
Demonstrated it is possible to vary kr, knr without significantly affecting other properties.