Some applications related to Chapter 11 material:
We will see how the kind of basic science we discussed in
Chapter 11 will probably lead to good advances in applied
areas such as:
1- Design of efficient solar cell dyes based on charge transfer
absorption.
2- Strongly luminescent materials based on the Jahn-Teller
effect.
1- Design of efficient solar cell dyes
based on charge transfer absorption
COO-
COO-
PO3-
PO3-
N
N
N
N
diimine
Pt
Pt
S
S
S
S
dithiolate
These complexes should have charge transfer from metal or ligand
orbitals to the p* orbitals.
CT-band for Pt(dbbpy)tdt
S
N
Pt
N
S
Data from: Cummings, S. D.; Eisenberg, R. J. Am. Chem. Soc. 1996, 118 1949-1960
X- Chloride
X-thiolate
dx2-y2
p*bpy
hv
CT to diimine
{
p (thiolate)
+
d p (Pt)
dxy
dxz-yz
dxz+-yz
dz2
Connick W. B.; Fleeman, W. L. Comments on Inorganic Chemistry, 2002, 23, 205-230
p bpy
70,000
500
N
60,000
S
S
S
450
O
400
e , M-1 cm-1 (NIR)
Pt
N
e , M-1 cm-1 (UV/VIS)
S
50,000
350
300
40,000
250
30,000
200
150
20,000
100
10,000
50
0
200
0
300
400
500
600
700
800
900 1000 1100 1200 1300 1400 1500 1600
Wavelength, nm
Electronic absorption spectra for dichloromethane solutions of (dbbpy)Pt(dmid), 1, (thin line) and
[(dbbpy)Pt(dmid)]2[TCNQ], 3, (thick line) in the UV/VIS region (left) and NIR region (right).
Smucker, B; Hudson, J. M.; Omary, M. A.; Dunbar, K.; Inorg. Chem. 2003, 42, 4717-4723
• So our data for Pt(dbbpy)(dmid) suggest that the lowest-energy absorptions are
transitions so the LUMO is dx2-y2
• The literature for Pt(dbbpy)(tdt) and for the M(diimine)(dithiolates) as a class
assigns the LUMO to be diimine p* instead of dx2-y2
• So is there something magical about dmid that changes the electronic
structure from that for analogous complexes with tdt and other
dithiolates???
• Or is the difference simply due to an instrumental technicality as Eisenberg and
Connick used UV/VIS instruments that only go to 800 nm while we used a
UV/VIS/NIR instrument that goes deep into the NIR (down to 3300 nm)?
•Let’s see….. we made Pt(dbbpy)(tdt) !!
N
S
S
S
S
Pt
N
S
N
O
Pt(dbbpy)(dmid)
Pt
N
S
Pt(dbbpy)(tdt)
Pt(dbbpy)tdt in CH2Cl2 1cm cell
2.5
2
1.5
Abs.
563nm
max
solid
1
0.5
0
200
563
400
600
800
1000
1200
1400
1600
Wavelength (nm)
1800
2000
2200
2400
Pt dbbpy tdt in CH3CN
0.8
S
Pt
0.7
S
N
526.5nm max
0.6
solid
0.5
Abs.
N
0.4
0.3
0.2
0.1
0
200
400
600
800
1000
Wavelength (nm)
1200
1400
1600
Pt(dbbpy)tdt in Dichloroethane
1
0.9
70mg/10mL stock
1ml-2ml
0.5ml-2ml
1:10ml
1:100ml
1mlof 1/100 -2
0.5ml of 1/100-2
1:1000ml
0.8
0.7
Abs.
0.6
0.5
0.4
0.3
0.2
0.1
0
250
350
450
550
650
750
Wavelength (nm)
850
950
1050
LUMO
hv
HOMO
Clearly a dx2-y2
orbital, not a
diimine p*
So the lowest-energy NIR bands are d-d transitions and the LUMO is indeed dx2-y2, not diimine p*
MO diagram for the M(diimine)(dithiolates) class!!!
dx2-y2
p*bpy
p*bpy
dx2-y2
{
p (thiolate)
+
d p (Pt)
{
p (thiolate)
+
d p (Pt)
dxy
dxz-yz
dxz+-yz
dz2
p bpy
Let’s hear it to Brian Prascher
who did the calculations!!
WHO CARES!!
The above was science, let’s now see
a potential application
• Silicon cells
– 10-20 % efficiency
– Corrosion
– Expensive (superior crystallinity required)
• Wide band gap semiconductors (e.g. TiO2;
SnO2; CdS; ZnO; GaP):
– Band gap >> 1 eV (peak of solar radiation)
– Solution: tether a dye (absorbs strongly across
the vis into the IR) on the semiconductor
– Cheaper!!… used as colloidal particles
Literature studies to date focused almost solely on dyes of Ru(bpy)32+
derivatives ==> Strong absorption across the vis region
(Grätzel; Kamat; T. Meyer; G. Meyer; others)
-
OO
O
O
N
N
-
PO3-
O3P
N
M
M
S
N
S
S
S
Anchoring groups on diimine to allow adsorption on TiO2 surface.
Pt dmeobpy tdt
0.98
dmeobpy = (MeOOC)2bpy
0.88
Precursor for the carboxylic acid (the ester is easier to
handle in organic solvents while the acid is soluble only in
aqueous base)
0.78
Abs.
0.68
0.58
solid
0.48
0.38
0.28
0.18
200
300
400
500
600
700
800
900 1000 1100 1200 1300 1400 1500 1600
Wavelenght (nm)
Cheaper is better!!
Ni(dmeobpy)tdt in CH2Cl2
O
3
0.4
O
0.35
2.5
S
N
0.3
Ni
2
S
N
Abs.
0.25
O
1.5
0.2
O
0.15
1
0.1
0.5
0.05
0
200
400
600
800
1000
1200
Wavelength (nm)
1400
1600
1800
0
2000
Ni(dcbpy)tdt solid vs Ni(dmeobpy)tdt solid
HO
1.2
O
1
S
0.8
N
Ni
S
N
0.6
O
0.4
HO
0.2
0
250
500
750
1000
1250
1500
1750
2000
2250
Wavelength (nm)
We’re testing this as a solar dye in Switzerland
…Stay tuned!!
2500
2- Strongly luminescent materials
based on the Jahn-Teller effect
a1'
p
e'
a2''(pz)
6p 0
6s0
e'(dxy,dx2-y2)
e''(dxz,dyz)
5d10
a1'(dz2)

[Au] +
(5d10)
[Au(PR3)3]+
PR3
Ground-state MO diagram of [Au(PR3)3]+ species, according to
the literature:
Forward, J.; Assefa, Z.; Fackler, J. P. J. Am. Chem. Soc. 1995, 117, 9103.
McCleskey, T. M.; Gray, H. B. Inorg. Chem. 1992, 31, 1734.
Molecular orbital diagrams (top) and optimized structures (bottom) for the 1A1’ ground state (left)
of the [Au(PH3)3]+ and its corresponding exciton (right).
Barakat, K. A.; Cundari, T. R.; Omary, M. A. J. Am. Chem. Soc. 2003, 125, 14228-14229
lem= 496 nm
lem= 478 nm
lem= 640 nm
[Au(TPA)3
]+
lem= 772 nm
QM/MM optimized structures of triplet [Au(PR3)3]+ models.
Barakat, K. A.; Cundari, T. R.; Omary, M. A. J. Am. Chem. Soc. 2003, 125, 14228-14229
WHO CARES!!
The above was science, let’s now see
a potential application
RGB bright emissions in the solid state and at RT are
required for a multi-color device….
AuL3 as LED materials?
• Glow strongly in the solid state at RT.
• But [Au(PR3)3]+ X- don’t sublime into thin
films (ionic).
• How about neutral Au(PR3)2X?:
– Do they also luminesce in the solid state at RT?
– Do they also exhibit Jahn-Teller distortion?
…let’s see the latest thing that made the Omary group
honors list!!
Omary group honors list, posted 11/22/03
BRAVO PANKAJ!
Experiment + Theory makes a good combo!
Excitation spectrum
l max = 500 nm
Intensity, arb units
l max = 320 nm
Emission spectrum
84.7
83.6
191.8
DFT calculations
(B3LYP/LANL2DZ) for
full model.
200
250
300
350
400
450
500
550
600
Wavelength, nm
• Experimental findings based on the solid-state
luminescence spectra at RT shown above:
1- The large Stokes’ shift (11, 200 cm-1), large fwhm (4,
700 cm-1), and the structurless profile all suggest a
largely distorted excited state.
2- The lifetime (21.6 ± 0.2 ms) suggests that the emission
is phosphorescence from a formally triplet excited state.
• To understand the nature of the excited state, Pankaj
did full quantum mechanical calculations (DFT) to fully
optimize the triplet excited state of the same compound
he is studying without any approximation in the model.
650
• In a recent paper (Barakat, K. A.; Cundari, T. R.; Omary, M. A.
J. Am. Chem. Soc. 2003, 125, 14228-14229), it was discovered
that a Jahn-Teller distortion takes place for cationic [AuL3]+
complexes (L=PR3) such that the trigonal geometry changes
toward a T-shape in the posphorescent triplet excited state.
• Pankaj shows in the figure above that the same rearrangement
toward a T-shape also takes place in the phosphorescent triplet
excited state of the neutral Au(PPh3)2Cl complex.
• This result explains the large Stokes’ shift in the experimental
spectra on the left.
•We’ll be probing the structure of the excited states of both AuL3
and AuL2X directly by “photocrystallography” and time-resolved
EXAFS to verify these calculated structures.