ECL Mechanism of ECL Mechanism of Ru(bpy)Ru(bpy)33

2+2+/TPrA System/TPrA System

N

N

N

N

N

N

Ru

2+

Ru(bpy)32+

ECL:Electrochemiluminesenceor Electrogenerated Chemiluminesence

(CH3CH2CH2)3N:

TPrA

(TriPropyl Amine)

(As coreactant)

IIECLECL & & IICVCV ~ ~ EE Profiles forProfiles forRu(bpy)Ru(bpy)33

22++(1 mM) /(1 mM) /TPrA TPrA (10 mM)(10 mM) SystemSystem(3 mm GC, 0.10 M PBS, pH 7, 100 mV/s)(3 mm GC, 0.10 M PBS, pH 7, 100 mV/s)

1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0-0.4

-0.2

0.0

0.2

0.4

CV

ECL

E (V va Ag/AgCl)

I CV(m

A)

-0.6

-0.3

0.0

0.3

0.6

IEC

L (mA

)

Direct Ru(bpy)Direct Ru(bpy)332+2+ Oxidation RoutesOxidation Routes

Elec

trode

eRu(bpy)3

3+

TPrA TPrAH+-H+e

hvRu(bpy)3

2+

TPrA.+ -H+

TPrA.

Ru(bpy)32+

H2O P2

Ru(bpy)32+*

P1

AlternativelyAlternatively

Ru(bpy)33+

Ru(bpy)32+

e

e

TPrA TPrAH+-H+

TPrA -H+TPrA.+ .

Ru(bpy)3+

P1

Ele

ctro

de

P2H2O

Ru(bpy)32+*

Ru(bpy)32+

hv

e

Ele

ctro

de Ru(bpy)32+

Ru(bpy)33+

TPrA TPrAH+-H+

TPrA -H+TPrA.+ .

Problems with the DirectProblems with the DirectRu(bpy)Ru(bpy)33

2+2+ Oxidation MechanismOxidation Mechanism

1. Mysterious ECL Pre-wave;

2. ECL at Labeled Magnetic Beads;

3. Proof of Energetic and Existence of Intermediates.

Ru(bpy)Ru(bpy)332+2+ Concentration Effects Concentration Effects

on on iiECLECL-- EE ProfilesProfiles

1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0

2nd

1st

iECL 300 nA/cm2

(b) 1 µM Ru(bpy)3

2+, i ECL

/160

(a) 1 mM Ru(bpy)3

2+, i ECL

/2x104

E (V, vs Ag/AgCl)

0.10 M TPrA + 0.20 M PBSpH 8, v = 20 mV/s, 3 mm GC

0.10 M TPrA/0.10 M Tris/0.10 M LiClO4pH 8, v = 50 mV/s, 3 mm GC

1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0

100 µA/cm2iECL

iCV 2.5 mA/cm2

(c) 1 nM Ru(bpy)3

2+

2nd

1st

E (V vs Ag/AgCl)

11stst ECL Peak Intensity vs ECL Peak Intensity vs ccTPrATPrA & & ccRu(bpy)Ru(bpy)332+2+

1E-8 1E-7 1E-6 1E-5 1E-4 1E-3 0.01 0.1 1 10

0.1

1

10

100

1000 (b) 100 mM TPrA

i EC

Lp1 (µ

A/c

m2 )

cRu(bpy)

3

2+ (mM)0 20 40 60 80 100

0

5

10

15

20

(a) 1µM Ru(bpy)3

2+

i EC

Lp1 (

µA/c

m2 )

cTPrA

(mM)

0.20 M PBS, pH ~ 8, 100 mV/s, GC

11stst & 2& 2ndnd ECL ResponsesECL ResponsesWhen When ccRu(bpy)Ru(bpy)332+ 2+ >= 0.050 mM>= 0.050 mM

1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0

0

5

10

15

cRu(bpy)

3

2+ (mM)

1.0 0.50 0.10 0.050

2nd

1st

(c) 100 m M T P rA

i EC

L (m

A/c

m2 )

E (V vs. Ag/AgCl)

0.20 M PBS, pH ~ 8, 100 mV/s, GC

ECL at Labeled Magnetic BeadsECL at Labeled Magnetic Beads

* = Ru(bpy)32+

**

* *

**

* **

*

4 µm

Electrode Electrode

+ E

SECMSECM--ECL Experimental SetECL Experimental Set--UpUp

Si NH2

5% 3-aminopropyltrimethoxysilan

SiO

2

OH

OH

OHBenzene, in Desiccator, 24 hr Si

O2

O

O

O

Schematic Structure of Silanized ITO Surface

Ru[(bpyMe2)]2[(bpy(COOH)2]2+

10 mM EDAC in1-methylimidazole(pH 7), 70oC for 45 min

Si NH

SiO

2

O

O

O

N

N

N

N

Ru*

CH3

CH3

HOOC

O

O2

ITO/OSiRuII

ITO

Silanization

Approach curve (tip current vs. distance)(φ =1.5 mm hemispherical Au at +0.85 V vs Ag/AgCl, in 10 mM

TPrA+100 mM LiClO4+100 mM Tris buffer (pH = 8) Soln)

-600 -500 -400 -300 -200 -100 00

2

4

6

8

10

12

14

-0.25 -0.20 -0.15 -0.10 -0.05 0.00 0.05 0.10 0.15

0

10

20

30

40

50

60

70

80

i T (µ

A)

d (µm)

i T (µA

)

d (µm)

TPrA TPrA+.

ITO

ECL Detection Without Touching ECL Detection Without Touching with Ru(bpy)with Ru(bpy)33

2+2+/ITO/ITO

1.0 0.8 0.6 0.4 0.2 0.0

-30

-20

-10

0

10

20

30

d = -5.0 µm (ITO/OSi---Ru(II))

CV ECL

E (V vs Ag/AgCl)

i CV (µ

Α)

-100

-75

-50

-25

0

25

50

75

100

iEC

L (pA)

Tip ~ Substrate Separation Effect Tip ~ Substrate Separation Effect on ECL Intensityon ECL Intensity

Notdetectable

7.68

604.80

693.84

862.88

922.40

1301.92

1331.44

1840.96

ECLIntensity

(pA)

- d (µm)

0 1 2 3 4 5 6 7 8 9

0

40

80

120

160

200

The data fitting equation

iECL

p = -5.13 + 219.75e0.289d (d <= 0)

Not detectable

i EC

Lp (pA

)

- d (µm)

TPrAH = TPrA + H+

TPrA+. TPrA .

0.88 V

P1-1.7 V-H+

E vs SCE

R u ( b p y ) 32 + *

R u ( b p y ) 33 + R u ( b p y ) 3

2 + R u ( b p y ) 3+

- 1 .0 6 V

0 .6 4 V

2 .1 2

eV

/ion

1 .0 6 V - 1 .4 8 V

E v s A g / A g C l

Proposed MechanismFor the 1st ECL Wave

A New Route for the Generation ofA New Route for the Generation ofRu(bpy)Ru(bpy)33

2+*2+* in Ru(bpy)in Ru(bpy)332+2+/TPrA /TPrA

SystemSystem

Elec

trod

e TPrA TPrAH+-H+

e

TPrA-H+

TPrA

.+

.

Ru(bpy)32+P1

Ru(bpy)3+ Ru(bpy)3

2+*

TPrA

+H+

hvRu(bpy)3

2+

Reaction Processes InvolvedReaction Processes Involvedfor the Oxidation of TPrAfor the Oxidation of TPrA

T P rA + H +T P rA H + p K a = 1 0 .4

T P rA.+ + e

T P rA.+ T P rA

. + H +

T P rA.

P 1 + H 2 O = P 2

T P rA.+

+ T P rA. = T P rA + P 1an d

T P rA

P 1 + e

k f

k bk s

k s

HalfHalf--life of TPrAlife of TPrA++.. Cation Radical Cation Radical Based on CV SimulationBased on CV Simulation

0 1 2 3 4 5 6 7 8 9 10

0.0

0.5

1.0

1.5

2.0

1.0 0.8 0.6 0.4 0.2 0.0

-50

-40

-30

-20

-10

0

A

i CV (µ

A/c

m2 )

E (Ag/Ag/Cl)

at p

oten

tial A

CTP

rA+. (µ

M)

x (µm)

TPrA+. TPrA. + H+kf

kf = 3500

τ2/1 = 0.693/kf ~ 0.2 ms

EPR EPR Detection of Detection of

TPrATPrA++..

Solution A: 0.03 M Ru(bpy)33+

Freshly Generated By Oxidized Ru(bpy)3

2+ Using Cl2

Solution B: 0.10 M TPrA at pH 7

Flow Rate: 2 to 5 mL/s

EPR Reference: Fremy’s Salt(K2[NO(SO3)2])

3 3 6 0 3 3 8 0 3 4 0 0 3 4 2 0 3 4 4 0 3 4 6 0 3 4 8 0 3 5 0 0 3 5 2 0 3 5 4 0

- 3 0 0 0

- 2 0 0 0

- 1 0 0 0

0

1 0 0 0

2 0 0 0

3 0 0 0

E P R o f TP rA + . o b ta ined by m ixin g 0 .03 M R u (bpy )3

3 + a n d0 .10 M T P r A ( p H = 7 ) s o lu t ions in a quar tz f l a t EPR ce l l

g = 2 . 0 0 3 8

Inte

nsity

M a g n e tic F ie ld (G )

Simulation

Simulation Parameters:14N (1N, I = 1), Hyperfine = 19.87G,

α−1H (6H, I = 0.5), Hyperfine = 20.05 G

Simulated EPR for TPrASimulated EPR for TPrA.

2 0 G

P a r a m e t e r s u s e d f o r t h e c a r b o n f r e e r a d i c a l s im u la t i o n :1 3 C ( 1 , I = 1 / 2 , h y p e r f i n e 2 0 G ) ,

α 1 H ( 1 , I = 1 / 2 , h f = 2 0 G ) , β 1 H ( 2 , I = 1 / 2 , h f = 1 8 G )

( C H3C H

2C H

2)

2N - C .H - C H

2C H

3

Fast Scan Cyclic VoltammetryFast Scan Cyclic Voltammetry

0.10 V/s,3mm GC

3mm GC

10 µm C Fiber

5 µm Pt

1.2 1.0 0.8 0.6 0.4 0.2 0.0

2 µA

TPA_sim_E&i

(d) v = 1000 V/s, i/60

(c) v = 100 V/s, i/30

(b) v = 1.0 V/s, i/5

(a) v = 20 mV/s

E (V)

Fast Scan CV Digital Simulations

900 V/s

1.2 0.8 0.4 0.0-5

-4

-3

-2

-1

0 (a)

DC

A

B

i CV (m

A/c

m2 )

E (V vs Ag/AgCl)

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

0

20

40

60

80

100

120

140

160 at potential A(b)

c (µ

M)

x (µm)

TPrA+. TPrA.

900 V/s

1.2 0.8 0.4 0.0-5

-4

-3

-2

-1

0 (a)

DC

A

B

i CV (m

A/c

m2 )

E (V vs Ag/AgCl)

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

0

20

40

60

80

100

120

140

160

at potential B(c)

TPrA+. TPrA.

c (µ

M)

x (µm)

900 V/s

1.2 0.8 0.4 0.0-5

-4

-3

-2

-1

0 (a)

DC

A

B

i CV (m

A/c

m2 )

E (V vs Ag/AgCl)

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

0

20

40

60

80

100

120

140

160

(d)

TPrA+. TPrA.

x (µm)

c (µ

M)

at potential C

900 V/s

1.2 0.8 0.4 0.0-5

-4

-3

-2

-1

0 (a)

DC

A

B

i CV (m

A/c

m2 )

E (V vs Ag/AgCl)

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

0

20

40

60

80

100

120

140

160

(e) at potential D

TPrA+. TPrA.

x (µm)

c (µ

M)

ConclusionsConclusions

TPrA+. is sufficiently stable in neutral aqueous solution to oxidize Ru(bpy)3

+ to generate Ru(bpy)3

2+*;

Under some ECE conditions, fast scan CV will not show short-lived species;

The ECL behavior of the Ru(bpy)32+/TPrA system is

complicated and involves several paths to the generation of excited state.

AcknowledgementAcknowledgement

Dr Allen J Bard Mr Jai-Pil Choi