The document discusses measuring the molar extinction coefficient of protoporphyrin IX (PPIX) films deposited on titanium dioxide (TiO2) using different solvents. It defines molar extinction coefficient and how it relates to light absorption.Graphs show extinction coefficient values of 1.49x105 M-1cm-1 for PPIX/TiO2 in DMF, 1.15x105 M-1cm-1 in THF, and 1.26x105 M-1cm-1 in a t-butanol:acetonitrile mix. DMF yielded the highest value. The extinction coefficient determines light harvesting efficiency and dye-sensitized solar cell performance.

1. Molar Extinction Coefficient For PPIX/TiO2 film in DMF,
THF & tBuOH:ACN(Mix.) Solvent
Dhruv Sharma

2. Importance of Molar Extinction Coefficient ( )
 Molar extinction coefficient is a measurement of how strongly a chemical species
absorb light at a given wavelength.
 It is an intrinsic property of chemical species i.e. it depend on chemical composition
and chemical structure of material, it independent on concentration.
 Measuring absorbance is a very fast method for determining the chemical
concentration, although the specific chemical species in the solution must be known.
Other method of measuring concentration, such as titration can take more time and
require additional chemicals.
The SI unit of ε are m2/mol but in practice they are usually taken as M-1cm-1 .
 Extinction coefficient allow us for estimation of molar concentration of solution
from its measured absorbance.

3. How to find Molar Extinction Coefficient?
Using the equation in an experiment
 Beer-Lambert Law use to find the Molar extinction coefficient. According to Beer-
Lambert’s law “When a monochromatic light beam pass through the homogeneous
solution, light absorb in the solution is directly proportional to the product of
concentration and path length.”
A =
or = A/cl
Where, I0 is incident light, I is transmit light, is molar extinction coefficient, A
represent absorbance, c is concentration, l is path length of light travel in the cuvette.

4.  The simple way to calculate it using the given formula.
 Define all the variables with a value. Absorbance (A), is a measurement without any
units, obtained from a spectrophotometer at a particular wavelength of light. Path length
is usually considered to be 1. Concentration of the substance (c) should also be known.
 Substitute these values in the equation mentioned for epsilon.
Using a Graph
 In a graph, several values of A are plotted on Y axis against a number of
concentrations on X axis.
 The slope of the line will be ε. Again here path length will be 1. Thus, the slope will
give you the molar absorptivity. Calculators are the easiest way to calculate these
values.

5. Application of Molar Extinction Coefficient
 Molar extinction coefficient is particularly useful in spectroscopy for measuring the
concentration of chemical solution.
 Molar extinction used to find the absorption cross section ( ), relation is given as
σ(λ) = Ɛ(λ) . 1000 (cm3L-1)
which gives the information of surface coverage ( ) on dye-sensitized solar cell,
given as
Г =A(λ)/σ(λ)
 Molar extinction coefficient is the intrinsic property of chemical species, so it use to
differentiate between different molecules.
 It use as a fingure print for molecule.
 Molar extinction coefficient use to define the range of wavelength where light has its
maximum depth of penetration in tissue.

6. Molar Extinction Coefficient of PPIX in DMF
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
350 400 450 500 550 600 650
Absorbance
Wavelength (nm)
Absorption Maxima = 405nm

7. Molar extinction coefficient of PPIX/DMF = 1.49 X 105 M-1cm-1
y = 0.149x
R² = 0.996
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 1 2 3 4 5 6
Absorbance
Concentration

8. Molar Extinction Coefficient of PPIX in THF
λmax = 406nm
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
350 400 450 500 550 600 650
ABSORBANCE
WAVELENGTH (nm)

9. Molar extinction coefficient of PPIX/THF = 1.15 X 105 M-1cm-1
y = 0.115x
R² = 0.995
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 1 2 3 4 5 6
ABSORBANNE
Concentration (10-6 M)

10. Molar Extinction Coefficient of PPIX in Mix (tBuOH:ACN)
-0.2
-0.1
1E-15
0.1
0.2
0.3
0.4
0.5
0.6
0.7
350 400 450 500 550 600 650
Absorbance
Wavelength (nm)
λmax = 403nm

11. y = 0.126x
R² = 0.994
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 1 2 3 4 5 6
Absorbance
Concentration
Molar extinction coefficient of PPIX/MIX = 1.26 X 105 M-1cm-1

12. Comparison between PPIX/TiO2 film in DMF, THF and Mix Solvent
Soret band Q band
PPIX λ (nm) ɛ (M-1cm-1) Q 1 Q2 Q3 Q4
ɛ (M-1cm-1)
λ
(nm) ɛ (M-1cm-1) λ (nm) ɛ (M-1cm-1) λ (nm) ɛ (M-1cm-1)
DMF 405 1.49 X 105 1.38 X 104 540 1.08 X 104 575 7.03 X 103 630 4.9 X 103
THF 406 1.15 X 105 1.06 X 104 538 8 X 103 577 4.7 X 103 632 4.1 X 103
MIX 403 1.26 X 105 1.12 X 104 537 9.4 X 103 575 5.6 X 103 628 4 X 103

13. Dielectric Constant List of Common Solvents Dielectric
Constant
Dipole
Moment

14. Conclusion
 It appears that selection of the appropriate solvent plays a role in improving the
efficiency of DSSC.
PPIX/TiO2 film show high extinction coefficient in DMF, then THF, Mix solvent.
Both DMF and THF are polar aprotic solvent, DMF (3.82 D) have high dipole moment
then THF (1.75 D) i.e. DMF have high polarity than THF.
High extinction coefficient means high absorption cross section, it light absorption
property.
 Surface coverage value depend upon, how the dye attach with TiO2 film, it not
depend on extinction coefficient.
 The light harvesting efficiency primarily governed by molar extinction coefficient of
dye.
 The high molar extinction coefficient sensitizer use to obtain high efficiency with
thinner TiO2 films.

15.  Investigation of extinction coefficient ( ) of PPIX/TiO2 film in DMF, THF, Mix solvents.
 Measure absorbance of PPIX/TiO2 film in DMF, THF, Mix solvent (at 1 X 10-4M) and
calculate the surface coverage value in respective solvent (Immersion solvent).
 Measure absorbance of PPIX/TiO2 film in DMF (1,3,5 X 10-5 M), THF ((1,3,5 X 10-5 M)),
Mix solvent ((1,3,5 X 10-5 M)) and calculate the Kadsorption value in respective solvent.
 Measure absorbance of PPIX/TiO2 in DMF solvent (concentration 1 X 10-4M ) 1hour, 3 hour, 5
hour (Immersion Time).
 To study the change in light harvesting efficiency (L.H.E) with immersion solvent, immersion
time, immersion concentration respectively.
 To study the change in surface coverage value ( ) with immersion solvent, immersion time,
immersion concentration respectively.
To study the effect of different solvent to control the aggregation and adsorption kinetics for
increase the efficiency of DSSC performance.
 To make the highly transparent TiO2/PPIX films..
 To study the electron injection and charge recombination study by using Steady state and time
resolved fluorescence spectroscopy.
Scope of Project