Semi-empirical computation of selected molecular properties of polyisothianaphthene and its derivatives as influenced by doping

Date

3-2009

Degree

Bachelor of Science in Chemistry

College

College of Arts and Sciences (CAS)

Adviser/Committee Chair

Ernesto J. del Rosario

Abstract

ABSTRACT

USTARIS, CHARISSA GONZALES. University of the Philippines at Los Banos, March 2009. Semi- empirical Computation of Selected Molecular Properties of Polyisothianaphthene and its Derivatives as Influenced by Doping.

Adviser: Dr. Ernesto J. del Rosario

Semi- empirical computation (using Hyperchem® 7.5/8.0 software) on four low band gap polymers, namely polyisothianaphthene (PITN), polyisonaphthothiophene (PINT), poly(5-methylben-zo[c]thiophene) (PMBT) and poly(1,3-dihydro-5,6- dioxymethyleneisothianaphthene) (PDOMIT) was done to determine selected molecular properties influencing the electrical conductivity of the said polymers in the undoped and doped states. The Restricted Hartree- Fock (RHF) method was employed for the undoped forms while the Unrestricted Hartree- Fock (UHF) was used for the doped forms. Both undoped and doped forms for the aromatic and quinoid structures were drawn and optimized and the molecular properties were computed after single point calculation using the PM3 method. The presence of dioxymethylene group, fused ring and alkyl group resulted in increased mean polarizability (a) and bandwidth, as well as decreased total energy (Ebinding) and binding energy (Ebinding. The presence of both fused ring and alkyl group resulted in increased dipole moment (p) and decreased electron affinity (EA). Both dioxymethylene and alkyl groups reduced the band gap (E„) and ionization potential (tP). The presence of the fused ring alone resulted in increased E„ IP, Atli and LUMO energy (Et,,,,to) and decreased HOMO energy (Enono), the dioxymethylene group alone increased Ellomo and EA and decreased ELumo and p. The presence of the alkyl group alone resulted in increased FMO energies. Doping of PITN, PINT, PMBT and PDOMIT resulted in a decrease in FMO energies and Egap and increase in IP, EA, bandwidth, p, u, a, Etotal and Ebinding. The magnitude of partial charges along the C=C and C-S path for P1TN, PINT, PMBT and PDOMIT increased with the doping level. For the average partial charge distribution per ring, the partially doped forms (polarons) showed maximal partial charge at the center of the chain while the fully doped forms (bipolarons) had two maximal partial charges located near the two terminals of the chain. Lower Egap and higher EA, IP, bandwidth, p and a were observed to be correlated with greater conductivity. Among the four polymers studied, PDOMIT is expected to have the highest conductivity due to its lower Egap higher a, and greater bandwidth. Based on its A,H, PDOMIT is also the easiest polymer to be formed. It is also the most stable in terms of Etotal

Language

English

Location

UPLB Main Library Special Collections Section (USCS)

Call Number

Thesis

Document Type

Thesis

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