1. Fluorometric Measurement of the Rate Constant and Reaction
Mechanism for Ru(bpy)3
2+
Phosphorescence Quenching by O2
Rashid Alsuwaidi, Chris Lieb, Chris Russell and Ralph Eachus
Department of Chemistry, The Pennsylvania State University, University Park, PA 16802
Submitted: March 24, 2014 (CHEM 457, Section 2)
Abstract
In this experiment, a nanosecond laser photolysis technique is used to find the rate
constants of Ru (bpy)3
2+.There three rate constants which are phosphorescence quenching,
spontaneous fluorescence decay and nonradiative relaxation. The three samples were air
saturated, oxygen saturated and nitrogen saturated and where exposed to a laser pulse at 337 nm.
The rate constant kq, was measured to be 3.008x1011±2.740x1010 M-1 s-1 .The kf+knr which is the
sum of the rate constant for fluorescence and nonradiative relaxation was measured to be
3.67x106±8.98x105 s-1.
Introduction
An atom needs energy to go from the ground to excited state when it absorbs a photon
from the 337 nm pulse laser which lasts for nanoseconds.2 When excited Ru (bpy)3
2+ relaxes by
fluorescence as shown in Figure 1.
*Ru (bpy)3
2+
𝑘 𝑓
→ Ru(bpy)3
2+ + hν
Figure 1. Relaxation of Ru (bpy)3
2+ by Fluorescence
Kf is the rate constant, *Ru (bpy)3
2+ is the excited state,and hv is light.
Another method it could relax is by nonradiative process shown in Figure 2.
*Ru (bpy)3
2+
𝑘 𝑛𝑟
→ Ru(bpy)3
2+ + heat
Figure 2. Relaxation of Ru (bpy)3
2+ by a Nonradiative process

2. Another method of relaxation is by quenching of Ru (bpy)3
2+ with oxygen as shown in
Figure 3.
*Ru (bpy)3
2+ + O2
𝑘 𝑞
→ Ru(bpy)3
3+ + O2
-
Figure 3. Relaxation of Ru (bpy)3
2+ by Oxygen Quenching
The rate of and concentration of the excited Ru (bpy)3
2+ are first order as shown in
Equation 1.
-d[*Ru(bpy)3
2+]/dt = kf[*Ru(bpy)3
2+] (1)
The rate of and concentration of the excited Ru(bpy)32+ and iodide anion are second order as
shown in Equation 2.
-d[*Ru(bpy)3
2+]/dt = knr[*Ru(bpy)3
2+] (2)
The rate of and concentration of the excited Ru(bpy)32+ and oxygen are second order as shown
in Equation 3.
-d[*Ru(bpy)3
2+]/dt=kq[*Ru(bpy)3
2+][O2] (3)
A constant k’ is related to the oxygen quenching rate by Equation 4.
k’=kq[O2] (4)
Equation 5 is used to measure the rate constant observed.
kobs = kf + knr + k’ (5)
Experimental Method
The three samples were air saturated, oxygen saturated and nitrogen saturated and where
exposed to a laser pulse at 337 nm. The samples were each purge for 8 minutes before testing.

3. Figure 4. Spectroscopy setup
The laser pulse excites the samples at 337 nm. A filter is needed for protection from the
laser. The intensity of each was recorded.
Results and Discussion
The rate constant for quenching, kq, was measured to be 3.008x1011±2.740x1010 M-1 s-1
.Kf and knr, were measured to be 3.67x106±8.98x105s-1 .The plot in Figure 8 shows the kobs of
each sample.
An absorbance spectrum was performed to show that Ru (bpy)3
2+ can absorb light at a
wavelength of 337nm. A plot of intensity versus time for each sample was created as shown in
Figure 8.

4. Figure 8. Intensity vs. Time
An exponential fit was made for each trend line. From these equations the constant, kobs is
determined for each sample. The rate constant decreases as the concentration of oxygen in
solution decreases. The highest is the nitrogen and the lowest is the oxygen sample. It’s because
the oxygen is allowing it to quench faster.
To find the quenching constant, kq the observed constant vs oxygen was as shown in
Figure 9. Using Henry’s Law the oxygen concentration in solution was determined as shown in
Table 1.
0
0.01
0.02
0.03
0.04
0.05
0.06
0.00E+00 5.00E-07 1.00E-06 1.50E-06 2.00E-06
FluorescenceIntensity
Time (s)
Ru(bpy)3
2+ Fluorescence
Nitrogen Saturated
Oxygen Saturated
Air Saturated
Expon. (Nitrogen
Saturated)
Expon. (Oxygen
Saturated)
Expon. (Air Saturated)
Trend line Equations
Nitrogen y=0.0531e
-2.98E+06x
Saturated: R
2
=0.9950
Oxygen y=0.0436e
-5.90E+06X
Saturated: R
2
=0.9893
Air y=0.042e
-5.06E+06x
Saturated: R
2
=0.9885

5. Figure 9. (area)°/(area) vs. concentration of oxygen
Sample
Oxygen Concentration
(M) (area)°/(area)
N2 0 1
O2 0.00002335 7.057569296
Air 0.000004903 1.723958333
Table 1. Concentration of oxygen with relative area ratio
The quenching reaction, kq is the slope of the kobs vs oxygen. The value for kq is
3.008x1011±2.740x1010 M-1 s-1. The y-intercept represents the kf, +knr. The value for kf+knr is
3.67x106±8.98x105 s-1. Most of the errors are from using henrys law to find the oxygen
concentration so to be more accurate you have to measure the oxygen concentrations
Conclusion
The quenching rate constant, kq, was determined to be 3.008x1011±2.740x1010 M-1 s-1 and
the value for kf+knr was determined to be 3.67x106±8.98x105 s-1. As you increase the oxygen
quench you will get an increasing rate constant because it is decaying faster.
y = 267585x+ 0.7405
R² = 0.9918
0
1
2
3
4
5
6
7
8
0 0.000005 0.00001 0.000015 0.00002 0.000025
(area)°/(area)
Oxygen Concentration (M)
(area)°/(area) vs. concentrationof Oxygen

6. Acknowledgement
I would like to acknowledge Chris Lieb, Chris Russell and Ralph Eachus, who were the group
members that assisted in performing the experiment and data analysis. In addition; Dr.
Milosavljevic, teaching assistants Mr. Yuguang (Chris) Li and Ms. Jennifer Tan.