Experiment 12

Absorption Wavelength Prediction of a Conjugated Dye Series Using a Computational Method JORDAN HASKINS AMANDA PETTY GINO MOORE ANDREW FLEMING

Introduction In this experiment, we used the HMO and Spartan

computer programs in order to calculate the molecular orbital energies of the three conjugated dyes used in Experiment 11. The dyes used were: 1,1' diethyl-4,4'-cyanine iodide  1,1' diethyl-4,4'-carbocyanine  1,1' diethyl-4,4'-dicarbocyanine iodide 

Materials and Methods Instructions were followed from the handout given

by the instructor for Spartan ’04 and instructions from the Physical Chemistry Lab Manual for HMO by Trinity Software. Next the molecular orbital energies were calculated for each dye using both programs. Calculations were made to determine wavelength and frequency. These values and the FEMO values from Experiment 11 were compared.

1,1’-diethyl-4,4’-cyanine iodide

1,1’-diethyl-4,4’-carbocyanine iodide

1,1’-diethyl-4,4’-dicarbocyanine iodide

Calculations Equations: ΔE= LUMO – HOMO ΔE= hc/λ ν= c/λ

A

value of -75 kcal/mol was given in the lab manual for β (used for calculation of molecular orbital energy).

Results Dye

FEMO LUMO, (J)

FEMO HOMO, (J)

HMO LUMO, (J)

HMO HOMO, (J)

Spartan LUMO, (J)

Spartan HOMO, (J)

1,1’-diethyl4,4’-cyanine iodide

1.11 x 10-18

7.68 x 10-19

-6.89 x 10-20

5.66 x 10-20

-7.34 X 10-19

-1.70 X 10-18

1,1’-diethyl4,4’-carbocyani ne iodide

1.05 x 10-18

7.68 x 10-19

-6.01 x 10-20

7.40 x 10-20

-7.95 X 10-19

-1.57 X 10-18

1,1’-diethyl4,4’-dicarbocya nine iodide

1.00 x 10-18

7.68 x 10-19

-5.78 x 10-20

4.42 x 10-20

-8.01 X 10-19

-1.50 X 10-18

Results Dyes

ΔEFEMO (J)

ΔEHMO (J)

ΔESPTN (J)

1,1’-diethyl4,4’-cyanine iodide

3.38 x 10-19

4.08 x 10-19

9.69 x 10-19

1,1’-diethyl4,4’-carbocyanine iodide

2.77 x 10-19

4.36 x 10-19

7.77 x 10-19

1,1’-diethyl4,4’-dicarbocyanin e iodide

2.35 x 10-19

3.32 x 10-19

7.02 x 10-19

Results Dye

FEMO, λmax (m)

Percent Error

HMO, λmax (m)

Percent Error

Spartan, λmax (m)

Percent Error

1,1’-diethyl4,4’-cyanine iodide

5.90 x 10-7

0.36

4.87 x 10-7

17.2

2.05 x 10-7

65.2

1,1’-diethyl4,4’-carbocyani ne iodide

7.08 x 10-7

1.16

4.55 x 10-7

36.4

2.56 x 10-7

63.9

1,1’-diethyl4,4’-dicarbocya nine iodide

8.14 x 10-7

3.67

5.98 x 10-7

29.2

2.83 x 10-7

65.2

Results Dye

FEMO, λmax (m)

FEMO, ν at λmax (s-1)

HMO, λmax (m)

HMO, ν at λmax (s-1)

Spartan, λmax (m)

Spartan, ν at λmax (s-1)

1,1’-diethyl4,4’-cyanine iodide

5.90 x 10-7

5.08 x 1014

4.87 x 10-7

6.16 x 1014

2.05 x 10-7

1.46 x 1015

1,1’-diethyl4,4’-carbocyanin e iodide

7.08 x 10-7

4.24 x 1014

4.55 x 10-7

6.58 x 1014

2.56 x 10-7

1.17 x 1015

1,1’-diethyl4,4’-dicarbocyan ine iodide

8.14 x 10-7

3.69 x 1014

5.98 x 10-7

5.01 x 1014

2.83 x 10-7

1.06 x 1015

Discussion The FEMO and HMO calculations obtained from

these experiments were very similar in HOMO,LUMO, wavelength and frequency.

However, the values obtained from Spartan were not

similar. This could be due to Spartan’s inability to build these dyes perfectly planar.

Conclusions •The percent error for our Spartan value was higher than our percent errors for FEMO and HMO. This is due to the fact that Spartan could not produce planar molecules of the dyes. Therefore, the data produced by Spartan were not as accurate as those from HMO. •Thus, we concluded that the HMO software is more suitable for calculations such as these.

Citations Clark, Roy W.; Howard, James C. Physical Chemistry Lab Manual, 4th ed., RonJon Publishing, Denton, TX, 1996. Fleming, A.J.; Physical Chemistry Laboratory Notebook, 2007 p. 12-14. Haskins, J.R.; Physical Chemistry Laboratory Notebook, 2007 p. 19-20. Moore, L.G.; Physical Chemistry Laboratory Notebook, 2007 p. 14-15. Petty, A..; Physical Chemistry Laboratory Notebook, 2007 p. 12-14. Howard, James C. Spartan ’04 for Windows Instructions.