K. George ThomasPhotosciences & Photonics Group

National Institute for Interdisciplinary Science and Technology (NIIST), CSIR, Trivandrum- 695 019, INDIA

(kgt@vsnl.com)

Optical Properties of Hybrid

Nanomaterials

Research Activities

1. Hybrid nanomaterials for optoelectronic applications

2. Design and study of organic nanostructured materials

3. Light induced processes in functional molecular systems

4. Functional control of molecules on surfaces

5 nm 20 nm

Au nanoparticles Au nanorods Quantum dots

Size and shape does matter….

Physical and chemical properties of matter in the

nanometer scale are distinctly different than in the

macroscopic scale

NIIST NIIST NIIST

Au nanorods

Surface Plasmon (SP) is the collective oscillation of free electrons under the influence of electromagnetic radiation

Shape anisotropy leads to the splitting of surface plasmon bands

Three identical SP modes

Transverse

absorption

Longitudinal

absorption

5 nm 20 nm

Gold nanoparticles and nanorods

400 500 600 700 800 9000.00

0.15

0.30

0.45

0.60

Sphere

Ab

so

rba

nc

e

Wavelength, nm

rod

Extinction Coefficient (λλλλmax - 700 nm) 0.53 x 1010 M-1cm-1

NIISTNIIST

dcore

dML

core

monolayer Coupling of

the size and shape dependent optoelectronic properties of nanomaterials

+the intrinsic functionalities of molecular systems (binding, self-assembly, switching etc.)

S SS

SSS

SS

George Thomas and P. V. Kamat,

Acc. Chem. Res. 2003, 888

George Thomas, Binil and Sudeep,

Pure & Appl Chem. 2002, 74, 1731

H2NH2C

J. Am. Chem. Soc. 2000,

122, 2655-2656

N+

Br

N+

N+ N+Br

N+Br

Br

Br

N+

Br

N+

N+ N+Br

N+Br

N+Br

Br

Br

Langmuir 2002, 18, 3722-3727.

N+

Br

N+

N+ N+Br

N+Br

Br

Br

H215

N-H2C

N+

Br

N+

N+N+Br

N +Br

Br

Br

SCN

O

S

O

S

O

S

OS

O

S

O

S

S

SS

SS

S Au

NCH3

O

S

NH3C

O

S

N CH3

O

S

NH3C O

S

NCH3

O

S

NH3C

O

S

S

SS

SS

S Au

N

H3CCH 3

O

O2N

S

N

H3C

H3C

O

NO 2

S

N

CH 3H3C

O NO 2

S

N

CH 3

CH 3O

O2N

S

N CH 3

CH 3

O

NO 2

S

Au-SP

J. Phys. Chem. B 2002,

106, 18-21

J. Am. Chem. Soc. 2003,

125, 7174-7175

Nano Lett. 2002, 2, 29-35

O

S

O

S

O

S

OS

O

S

O

S

S

SS

SS

S Au

NCH3

O

S

NH3C

O

S

N CH3

O

S

NH3C O

S

NCH3

O

S

NH3C

O

S

S

SS

SS

S Au

N

H3CCH 3

O

O2N

S

N

H3C

H3C

O

NO 2

S

N

CH 3H3C

O NO 2

S

N

CH 3

CH 3O

O2N

S

N CH 3

CH 3

O

NO 2

S

Au-SP

J. Phys. Chem. B 2002,

106, 18-21

J. Am. Chem. Soc. 2003,

125, 7174-7175

Nano Lett. 2002, 2, 29-35

Organic-inorganic hybrid nanomaterials

S SS

SSSSS

How polar is Au nanoparticle surface ?How polar is Au nanoparticle surface ?

CH2O(CH2)5SH CH2O(CH2)8SHCH2SH

III/I peak = 1.18III/I peak = 0.98III/I peak = 0.89

Binil and K. George Thomas J. Phys. Chem. B, 108, 13265 (2004)

Hybrid nanomaterials for charge transferH3C

Ru

NN

NN

N

N

S

S OO OCH3

S

O O

OCH3

2+

2PF6-

Au

Au-Ru2+

J. Phys. Chem. B., 110, 20737 (2006)

J. Phys. Chem. B. 111, 6839-6844 (2007)

S

S

S

Au

J. Phys. Chem. B., 106, 18 (2002

hννννAu

A

B

Au

e

Electron Transfer to Metal Nanocore

Au

hνννν’excimer/

exciplexes

C

(polar solvents)

Unquenched Component

……

bulk Au metal< 3 nm nanoparticle of Au

(conductor) (insulator ?)

unoccupied

occupied

particles

Eg

metal

What are the main deactivation pathways of the photoexcited

fluorophore bound to a metal nanoparticle/QD’s ?

Chromophore Functionalized Metal/QD’s(i) Effect of spacer(ii) Core size (iii) Redox properties

George Thomas and coworkers J. Phys. Chem. B., 106, 18 (2002)

In Situ Synthesis of Metal Nanoparticles

COOH

OH

OHHO

COOH

O

OHO

2H+2e-

O

O

O

O

O

O

OO

O

O

O

O

OO

O

H

H

H

H

H

O

O

O

O

O

O

OO

O

O

O

O

OO

O

H

H

H

H

H

400 600 800 10000.0

0.4

0.8

0 600.0

0.2

0.4

0.6

Ab

so

rban

ce

Wavelength, nm

iii

ii

i

A53

0 n

m

Time, s

100 nm100 nm100 nm100 nm100 nm

400 6000.0

0.1

0.2

0 200 4000.00

0.05

0.10

0.15

Ab

so

rba

nce

Wavelength, nm

A420 n

m

Time, s

i

ii

iii

100 nm100 nm 100 nm100 nm

Hybrid nanomaterials as biosensors

NIISTNIIST

NIISTNIIST

400 500 600 7000.0

0.5

1.0

pH 4.5

Pb2+

Ab

so

rba

nc

e

Wavelength, nm400 600 800

0.5

1.0

Hg2+

pH 4.5

Ab

so

rban

ce

Wavelength, nm

Selective ‘Naked-Eye’ Detection of Lead Ions from Aqueous Media

0 100 200 300

0.8

0.9

1.0

0 10 20 30 40 50

0

4

8

12

Ag nanoparticle

A456/A

429

[Mn+

], µµµµM

∆λ

∆λ

∆λ

∆λ

max n

m

[Pb2+

], µµµµM

CaII PbII CdII MgII ZnII NiIICaII PbII CdII MgII ZnII NiII CaII PbII CdII MgII ZnII NiIICaII PbII CdII MgII ZnII NiII

Fe3+, Cd2+, Cu2+, Hg2+, Ni2+, Zn2+, Mg2+ & Ca 2+.

Pb2+ ions (i) variable co-ordination number up to 12 (ii) flexible bond length (up to 3

Å) and co-ordination geometry.

Yoosaf, Binil, Suresh and George Thomas, J. Phys. Chem. C 111, 12839 (2007)

Au Au Au

N

NSH2C CH3=

BT

Eu3+/ Tb3+

Au Au Au

N

NSH2C CH3=

BT

Eu3+/ Tb3+

AuAu AuAu AuAu

N

NSH2C CH3=

BT

Eu3+/ Tb3+

B. I. Ipe, K. Yoosaf, GeorgeThomas

J. Am. Chem. Soc. 128, 150 (2006)

ΦΦΦΦ τ, τ, τ, τ, ms

Eu-AuBT

Tb-AuBT

0.009

0.038 0.56

0.4

Complex

300 350 600 650 7000

2

4

6

8

10

Eu3+

Inte

nsi

ty (

a.u

.)

Wavelength, nm

Phosphorescent nanomaterials as biosensors

RCH2CH(NH3)CO2

360 nm

520 nm

N

O

NO2

R

NH3

O----

O----

O+

O+

S

CH3

CH3

CO

O

H

Au-MC-amino acid complex

Au

Light-mediated binding and release of amino acid derivatives

Au-MC

360 nm

hνννν /∆/∆/∆/∆

N

H3C CH3

S

O NO2

ON

O

NO2

O----

S

H3CCH3

+

Au-SP

AuAu

Binil, Mahima and George Thomas J. Am. Chem. Soc. 125, 7174 (2003)

HO

HO

NH3

O2CO----

O+

DOPA

Nanostructures of noble metals can convert photons into surface plasmon and within the propagation length, the surface plasmon modes can be decoupled back to light.

Surface plasmons are not diffraction limited

Miniaturizing of devices-propagation of light at nanoscale

Design of nanoscale optoelectronic and photonic devices

Atwater and coworkers Naturematerials, 2003, 2, 229

Can we integrate nanorods into higher order assemblies and tune their optical responses ?

EE

aabb

cc

aabb

cc

BB

EE

aabb

cc

aabb

cc

AA

new red shifted band new blue shifted band

Gluodenis and Foss, J. Phys. Chem. B 106, 9484 (2002).

Theoretical studies on plasmon coupling

Also refer – Schatz and coworkers

El-Sayed and coworkers

Liz-Marzán and coworkers

Mulvaney and coworkers

Cortie and coworkers

Murphy and coworkers

• The end faces of Au nanorods are

dominated by {111} planes and the

side facets by {100} and {110} plane

(El-Sayed and coworkers

Murphy and coworkers)

• Thiols preferentially bind to the

{111} planes of the Au rods

Murphy and coworkers; J. Am. Chem. Soc., 125, 13914 (2003)

• supramolecular approach

• covalent linking

nHierarchical integration of nanomaterials

Crystallographic facets of Au nanorods

Au 111

Au 110 or 100

Crystallographic facets of Au nanorods

Au 111

Au 110 or 100

n

George Thomas and coworkers J. Phys. Chem. B, 108, 13066-13068 (2004).J. Am. Chem. Soc., 127, 6516-6517 (2005). J. Phys. Chem. B, 110, 150-157 (2006).

J. Am. Chem. Soc. 129, 6712-6713 (2007).

Adv. Mater. (2008) (DOI: 10.1002/adma.200703057)

Hierarchical integration of nanomaterials and plasmon coupling

Thomas, K. G., chapter entitled “Surface plasmon resonances in nanostructured materials,”

in Nanomaterials chemistry: Novel aspects and new directions, Rao, C.N.R.; Mueller. A.; Cheetham A. K. (Eds.) Wiley-VCH (2007) pp 185-216.

Connecting nanorods-supramolecular approach

with concentration with time

0 – 8.0 µµµµM15 µµµµM

0-120 min

400 600 800 1000 12000.0

0.2

0.4

0.6

g

a

Ab

so

rba

nc

e

Wavelength, nm

C

SCH2C

OH

O

Au CCH2S

O

HO

Au

George Thomas et al., J. Phys. Chem. B 2004, 108, 13066

400 600 800 1000 12000.0

0.1

0.2

0.3

0.4jd

c

b

a

Ab

so

rba

nc

e

Wavelength, nm

D

HS C

OH

O

Binding unitAssist self assembly

n

400 600 800 1000 12000.0

0.2

0.4

0.6

g

a

Ab

so

rba

nc

e

Wavelength, nm

C 50 nm

50 nm 50 nm

50 nm

B

C D

A

50 nm

50 nm 50 nm

50 nm

B

C D

A

NIIST

NIIST

NIIST

NIIST

1,3-propanedithiol (C3-DT)

1,9-nonanedithiol (C9-DT)

1,8-octanedithiol (C8-DT)

1,6-hexanedithiol (C6-DT)

1,5-pentanedithiol (C5-DT)HS SH

HSSH

HSSH

HS SH

HS SH

nnn

αααα,ωωωω-dithiols

~0.12 nM of Au nanorods S. T. S. Joseph, B. I. Ipe, P. Pramod and

K. George Thomas,

J. Phys. Chem. B., 110, 150 (2006)

Connecting nanorods-covalent approach

Gold nanorods to nanochains

HSHSHSHSSSSS

SHSHSHSH

SSSSSSSS

SHSHSHSH

SHSHSHSH

SSSS

SHSHSHSH

SSSSSSSS

SHSHSHSH

n

SHSHSHSH

SHSHSHSH

SHSHSHSH

SHSHSHSH

SSSS

SSSS

SSSS

SSSSSSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSSSSSS

SSSS

SSSSHSHSHSHS

HSHSHSHSHSHSHSHS

HSHSHSHS

n

n/2

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSSSSSS

SSSSSSSS

SSSS

SSSS

SSSSSSSS

SSSS

α,ω-dithiol

Step 1below critical

concentration

Step 2aabove critical

concentration

HSHSHSHSSSSS

SHSHSHSH

SSSSSSSS

SHSHSHSH

SHSHSHSH

SSSS

SHSHSHSH

SSSSSSSS

SHSHSHSH

n

SHSHSHSHSHSHSHSH

SHSHSHSHSHSHSHSH

SHSHSHSHSHSHSHSH

SHSHSHSHSHSHSHSH

SSSS

SSSS

SSSS

SSSSSSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSSSSSS

SSSS

SSSSHSHSHSHSHSHSHSHS

HSHSHSHSHSHSHSHS

HSHSHSHS

n

n/2

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSSSSSS

SSSSSSSS

SSSS

SSSS

SSSSSSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSSSSSS

SSSSSSSS

SSSS

SSSS

SSSSSSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSS

SSSSSSSS

SSSSSSSS

SSSS

SSSS

SSSSSSSS

SSSS

α,ω-dithiol

Step 1below critical

concentration

Step 2aabove critical

concentration

Step 2b

Shibu, Binil, Pramod, George Thomas, J. Phys. Chem. B 2006,110, 150

200 nm2 00 n m 200 n m

200 n m200 n m

A B

C

200 nm200 nm2 00 n m 200 n m

200 n m200 n m

2 00 n m 200 n m

200 n m200 n m

A B

C

500 s

1000 s

1500 s

600 800 1000 12000.0

0.2

0.4

0.648 min0

jhg

a

Ab

so

rban

ce

Wavelength, nm

NIIST

NIIST

NIIST

HSSH

HS

SH

Effect of linker group

1,6 hexane dithiol; C6DT(~0.84 nm)

1,4-pheylenedimethanethiol; PDT(~0.9 nm)

600 800 10000.1

0.2

0.3

0.4

0.5

0.6

840 nm

8 min0

Ab

so

rban

ce

Wavelength, nm

600 800 10000.0

0.2

0.4

0.6

5 min0

732 nm

Ab

so

rban

ce

Wavelength, nm

50 nm50 nm

Av. angle = 146°°°° Av. angle = 96°°°°

NIISTNIISTNIIST

NIIST

Pramod and George Thomas Adv. Mater. 2008

(DOI: 10.1002/adma.200703057)

SS SS SS SS

Au

nanorod

Au nanorod

λλλλmax = 730 nm λλλλmax = 840 nm

50 nm

50 nm

Flexible linkerFlexible linker Rigid linkerRigid linker

S S

S S

Au

nano

rod A

u

nanoro

d

Effective dipolar overlapEffective dipolar overlap

Probing nanomaterial-molecule junctions

NIIST

NIIST

S S

dimerizationdimerization

S S

50 nm 50 nm

~0.8 nm

NIISTNIIST

NIIST

NIIST

0 1 2 3 2000 4000

0.1

0.2

0.3

0.4

b & c

a

A

(900 nm)

Cysteine / µµµµM

400 600 800 1000 12000.00

0.15

0.30

0.45

0.60

0.75i

a

A

λλλλ / nm

BA

0 1 2 3 2000 4000

0.1

0.2

0.3

0.4

b & c

a

A

(900 nm)

Cysteine / µµµµM

400 600 800 1000 12000.00

0.15

0.30

0.45

0.60

0.75i

a

A

λλλλ / nm

BA

Selective Detection of Cysteine

50 nm 50 nm50 nm

A B C

50 nm 50 nm50 nm

A B C

50 nm 50 nm50 nm

A B C

S COO

NH3

S COO

NH3

S COO

NH3

S

OOC

H3N

S COO

NH3

S

OOC

H3N

S

OOC

NH2S COO

NH3

S

OOC

H3NS COO

NH3 N

N N N N NN N N

Br

N

NNNNN NNNNN

Br Br Br

Br

BrBrBr

BrBr

Br Br Br

Br

BrBrBr

Br

S COO

NH3

S

OOC

H3N

S COO

NH3

S

OOC

H3N

S

OOC

H3N

S

OOC

H3N

N

N N N

Br

N NN N N

Br

N

NNNNN NNNNN

Br Br Br

Br

BrBrBr

BrBr

Br Br Br

Br

BrBr

Br

Au Au Au Au

n

Oligomerization of gold nanorod through end to end self-assembly

Two point electrostatic interaction

HSC

NH3

O

O

NIIST

NIISTNIIST

600 800 1000 12000.00

0.15

0.30

0.45

0.60

0.75

h

a

Ab

so

rba

nc

e

Wavelength, nm

0.0

0.1

0.2

0.3

0.4

0.5

γγ γγ-G

lu-C

ys-G

ly

Met A

sn

Pro

Gln

Arg

Ser

Val

Trp

Tyr

Th

r

Leu

Lys Il

eH

is Gly

Ph

e Glu

Asp

Cys

Ala

∆∆∆∆ A

(900 n

m)

aminoacids/peptide

i) keeping the cysteine thiol group in proteins in the

reduced state and (ii) protecting the cells from

oxidative stress by trapping free radicals that

damage DNA and RNA.

[GSH]: 0 -15 µµµµM

Detection of Glutathione

P. K. Sudeep, S. T. S. Joseph and K. George Thomas,

J. Am. Chem. Soc., 127, 6517 (2005).

C

NH3

CN C

N C

O

H

O

O

O

H

OH

O

SH

Protects body from oxidative

stress

Plasmon coupling in Au nanorods

Dimerization

Oligomerization

400 500 600 700 800 9000.00

0.15

0.30

0.45

0.60

Ab

so

rba

nc

e

Wavelength, nm

600 800 100012000.0

0.2

0.4

0.648 min0jhg

a

Ab

so

rban

ce

Wavelength, nm

(900 nm)

400 600 800 1000 12000.00

0.15

0.30

0.45

0.60

0.75i

a

A

λλλλ / nm

A

(900 nm)

400 600 800 1000 12000.00

0.15

0.30

0.45

0.60

0.75i

a

A

λλλλ / nm

A

Au

Au Au

Au Au Au Au

Tasting Edge Effects

Bocquet, Am. J. Phys. 2007, 75, 148.

Divergence of electric field and charge accumulation at the edges or corners

Wang and co workers, small 2007, 3, 2103

Electric-field-intensity enhancement in nanoparticles and nanorods-FDTD calculation

Thomas F. Jaramillo, et al Science 2007, 317, 100

Identification of active edge sites for electrochemical H2 evolution from MoS2 nanocatalysts

Edges are very reactive

Edge effect

10 nm 5 nm 2 nm 2 nm

600 800 10000.00

0.15

0.30

0.45 ∆λ ∼ ∆λ ∼ ∆λ ∼ ∆λ ∼ 60 nm

ba

Ab

sorb

an

ce

Wavelength, nm

HRTEM studies

20 nm 5 nm

- +

Electric field at the edges of anisotropic nanostructures

NIIST

NIIST

NIIST NIIST

NIIST NIIST

-----

-

--

- -------

-

--

Au nanorods

++++

++ ++++

++

++++

+++

+++

++

++++

++

++++

++

++++

++

++++

++ ++++

++

++++

+++

+++

++

++++

++

++++

++

++++

++- - -

Pramod, Shibu and George Thomas

J. Am. Chem. Soc. , 129, 6712 (2007)

15

30

45

60

75

4.5

Aspect ratio3.73.0

2.25.7

1.8

Pla

smon

Sh

ift,

nm

Np size, nm

C

Optimizing the shell thickness of Quantum dots

0 1 2 3 40.0

0.2

0.4

0

100

200

αα αα, M

-1

ΦΦ ΦΦL

ZnS monolayers

Vinayakan. Shanmugapriya, Nair, Ramamurthy, George Thomas

J. Phys. Chem. C 111, 10146 (2007)

Electric field at the edges

NIIST NIISTNIIST

Self-organization of molecules on surface

PhenyleneethylenesPhenyleneethylenes…………..

Rigid

molecules

Maintains ππππ-

conjugation

George Thomas and coworkersJ. Phys. Chem. A 110, 4329-4337 (2006)

Can the optoelectronic properties of same molecules on surface modulated by varying their organization

J. Phys. Chem. A, 110, 5642-5649 (2006).

1.3 nm

Type II

OO

OO

OO

OO

OO

OO

OOa

b

) 70°

OO

O

O

O

O

O

O

O

O

O

O

O

O

) 83°

b

a

Type I

Yoosaf, James, Ramesh, Suresh, and George Thomas,

J. Phys. Chem. C. 111, 14933-14936 (2007).

NIIST NIIST

Functional control of molecules on surfaces - STM studies

Former doctoral students

Dr. V. Biju

Dr. Zeena S. Pillai Dr. P. K. Sudeep

Dr. Binil Itty Ipe

Dr. P. V. James

Dr. K. Yoosaf

Dr. S. T. Shibu Joseph

Dr. P. Pramod

R. Vinayakan

A. R. Ramesh Pratheesh V. NairJino George

Jatish Kumar M. Shantil Anoop Thomas

Present students

Professor M. V. George (NIIST)

Collaborators: Dr. Prashant V. Kamat (Notre Dame, USA)Dr. C. H. Suresh (NIIST)

Dr. P. Ramamurthy (University of Madras)

(i) CSIR (Government of India)

Professor T. K Chandrasekhar (Director, NIIST)

Dr. Suresh Das (NIIST)

Former Directors of NIIST

Members of Photosciences and Photonics Group

(ii) Nanoscience and Technology Initiative of DST(Government of India)

Funding from

Thank you