JORDAN HASKINSAMANDA PETTYGINO MOORE

ANDREW FLEMING

Absorption Wavelength Prediction of a Conjugated Dye Series Using a Computational

Method

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/λν= c/λ

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

Dye FEMO LUMO, (J)

FEMO HOMO, (J)

HMO LUMO, (J)

HMO HOMO, (J)

Spartan LUMO, (J)

Spartan HOMO, (J)

1,1’-diethyl-4,4’-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’-diethyl-4,4’-carbocyanine 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’-diethyl-4,4’-dicarbocyanine 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

Results

Dyes ΔEFEMO (J) ΔEHMO (J) ΔESPTN (J)

1,1’-diethyl-4,4’-cyanine iodide

3.38 x 10-19 4.08 x 10-19 9.69 x 10-19

1,1’-diethyl-4,4’-carbocyanine iodide

2.77 x 10-19 4.36 x 10-19 7.77 x 10-19

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

2.35 x 10-19 3.32 x 10-19 7.02 x 10-19

Dye FEMO, λmax (m)

Percent Error

HMO, λmax (m)

Percent Error

Spartan, λmax (m)

Percent Error

1,1’-diethyl-4,4’-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’-diethyl-4,4’-carbocyanine iodide

7.08 x 10-7 1.16 4.55 x 10-7 36.4 2.56 x 10-7 63.9

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

8.14 x 10-7 3.67 5.98 x 10-7 29.2 2.83 x 10-7 65.2

Results

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’-diethyl-4,4’-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’-diethyl-4,4’-carbocyanine 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’-diethyl-4,4’-dicarbocyanine 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

1. Clark, Roy W.; Howard, James C. Physical Chemistry Lab Manual, 4th ed., RonJon Publishing, Denton, TX, 1996.

2. Fleming, A.J.; Physical Chemistry Laboratory Notebook, 2007 p. 12-14.

3. Haskins, J.R.; Physical Chemistry Laboratory Notebook, 2007 p. 19-20.

4. Moore, L.G.; Physical Chemistry Laboratory Notebook, 2007 p. 14-15.

5. Petty, A..; Physical Chemistry Laboratory Notebook, 2007 p. 12-14.

6. Howard, James C. Spartan ’04 for Windows Instructions.