Mike Scudder CHEM 7350 November 15, 2017 - PowerPoint Presentation

Slide1

Mike Scudder

CHEM 7350

November 15, 2017

d

6

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

Cyclometalated

iridium complexes

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

Cyclometalated

iridium complexes

Absorption and emission spectra of (

ppy

)

2

Ir(

acac

)

2

OLEDs

LECs

Current density (open squares) and luminance (triangles) vs time at 4V bias in an

Ir

(ppyPbu

3

)

3

:(PF

6

)

3

3

Exhibit wide color tunability, high phosphorescence

Φ

Photophysical

, electrochemical properties crucial for materials performance

Dye-sensitized solar cells

1

Controlling emission wavelength in

Ir

complexes

Ancillary ligands

blueshift

the absorption and emission energies by stabilizing HOMO, leaving LUMO unchanged

Destabilization of the

1

MLCT state results in a decreased

1MLCT character in the lowest excited state, becomes more ligand-localized

Thompson et al. Inorganic Chemistry 2005 44 (6), 1713-1727

Controlling

k

r

,

k

nr

in iridium complexes

Excited-state lifetimes and quantum yields are used to calculate

k

r

, knrkr: based on the amount of metal character in emitting excited state, energy gap between singlet and triplet states

k

nr

: intramolecular

vibronic

coupling and thermal accessibility of metal-centered states

Thompson et al.

Inorganic Chemistry

2005 44 (6), 1713-1727

Structural modifications of

Ir

complexes

Potential (V vs Fc+/Fc)

Current

k

nr

k

r

3

A

1

A*

1

A

ISC

E

phosphorescence

hν

-E

fluorescence

hν

“Static Properties”

“Dynamic Properties”

Both static and dynamic properties sensitive to complex architecture

Motivation

: Find design approach to allow variation of

k

r

,

k

nr

independently of redox potential and emission maximum

Synthetic Approach: Tris-

heteroleptic

complexes

Not emissive at room temp.

Cyclic voltammetry results (complexes 1-10)

E

ox

(V)

0.43

0.73

0.58

E

ox

(V)

0.49

0.79

0.64

E

ox

(V)

0.45

0.75

0.61

0.60

Cyclic voltammetry results (isomers)

E

ox

(V)

0.73

0.72

0.76

0.73

Each diastereomer contains at least one pyridine group: quasi-reversible redox

Replacing

acac

with pic: shifts both potentials by 150 mV

UV-Vis results

LC

1

ππ

*

MLCT

Direct population of

3

A

Ppz

ligand: not emissive at room temperature

Replacing

ppy

with

ppz

has negligible effect on redox potentials, emission spectra

Significant impact on

k

r

,

k

nr

UV-Vis results

Emission maxima dictated by the overall number of fluorine substituents on the complexes

Complex 5: Not emissive at room temperature

UV-Vis results

Placement of F on ligand: no effect on redox/emission maxima

Significant effect on

k

r

,

k

nr

UV-Vis results: tris-

heteroleptic

isomers

Unlike

acac

, pic is asymmetric and

nonchromophoric

Resulted in

blueshift

relative to

acac complexesIsomers a and b: very similar absorption spectra

Close similarity confirmed by theory

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

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.