Some applications related to Chapter 11 material:
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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.

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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


diimine

dithiolate

These complexes should have charge transfer from metal or ligand orbitals to the p* orbitals.


CT-band for Pt(dbbpy)tdt

Data from: Cummings, S. D.; Eisenberg, R. J. Am. Chem. Soc.1996, 118 1949-1960


X- Chloride

X-thiolate

dx2-y2

*bpy

hv

CT to diimine

{

 (thiolate) +

d  (Pt)

dxy

dxz-yz

dxz+-yz

dz2

Connick W. B.; Fleeman, W. L. Comments on Inorganic Chemistry, 2002, 23, 205-230

 bpy


70,000

500

450

60,000

400

50,000

(NIR)

350

(UV/VIS)

-1

300

cm

40,000

-1

250

-1

, M

cm

30,000

e

200

-1

, M

150

e

20,000

100

10,000

50

0

0

200

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) !!

Pt(dbbpy)(dmid)

Pt(dbbpy)(tdt)


563


LUMO

Clearly a dx2-y2 orbital, not a diimine p*

hv

HOMO


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

*bpy

*bpy

dx2-y2

{

{

 (thiolate) +

d  (Pt)

 (thiolate) +

d  (Pt)

dxy

dxz-yz

dxz+-yz

dz2

 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


Solar Energy Conversion

  • 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)


Anchoring groups on diimine to allow adsorption on TiO2 surface.


dmeobpy = (MeOOC)2bpy

Precursor for the carboxylic acid (the ester is easier to handle in organic solvents while the acid is soluble only in aqueous base)

solid


Cheaper is better!!


We’re testing this as a solar dye in Switzerland

…Stay tuned!!


2- Strongly luminescent materials based on the Jahn-Teller effect


0

0

10

[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= 772 nm

lem= 640 nm

[Au(TPA)3]+

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!

DFT calculations (B3LYP/LANL2DZ) for full model.

  • 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.

  • 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.


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