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

Dhruv Sharma

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.

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.

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.

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.

Molar Extinction Coefficient of PPIX in DMF

350 400 450 500 550 600 6500

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Wavelength (nm)

Abso

rban

ce

Absorption Maxima = 405nm

Molar extinction coefficient of PPIX/DMF = 1.49 X 105 M-1cm-1

0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.50

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

f(x) = 0.149693869187273 xR² = 0.999317118658458

Concentration

Abso

rban

ce

Molar Extinction Coefficient of PPIX in THF

λmax = 406nm

350 400 450 500 550 600 650

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

AB

SOR

BA

NC

E

WAVELENGTH (nm)

Molar extinction coefficient of PPIX/THF = 1.15 X 105 M-1cm-1

0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.50

0.1

0.2

0.3

0.4

0.5

0.6

0.7

f(x) = 0.115410661432727 xR² = 0.999052594480726

AB

SOR

BA

NN

E

Concentration (10 -6 M)

Molar Extinction Coefficient of PPIX in Mix (tBuOH:ACN)

350 400 450 500 550 600 650

-0.0999999999999994

5.82867087928207E-16

0.100000000000001

0.200000000000001

0.300000000000001

0.400000000000001

0.500000000000001

0.600000000000001

0.700000000000001

Wavelength (nm)

Abso

rban

ce

λmax = 403nm

0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.50

0.1

0.2

0.3

0.4

0.5

0.6

0.7

f(x) = 0.126183388072727 xR² = 0.998855184994628

Concentration

Abso

rban

ce

Molar extinction coefficient of PPIX/MIX = 1.26 X 105 M-1cm-1

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

Dielectric Constant List of Common Solvents Dielectric Constant

Dipole

Moment

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.

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