Date of Award

Spring 1999

Document Type

Restricted Thesis

Terms of Use

© 1999 Jonathan Pyle. All rights reserved. Access to this work is restricted to users within the Swarthmore College network and may only be used for non-commercial, educational, and research purposes. Sharing with users outside of the Swarthmore College network is expressly prohibited. For all other uses, including reproduction and distribution, please contact the copyright holder.

Degree Name

Bachelor of Arts


Physics & Astronomy Department

First Advisor

Daniel P. Aalberts


The cis to trans photoisomerization of retinal, a common biomolecular photon detector, is modeled using the Su, Schrieffer, and Heeger model of conjugated polyenes and the extended Hubbard model of electronic interactions. This attempt improves on previous attempts by shedding the mean-field approximation, and by treating photoisomerization as a current acting on electrons in the pz orbitals of carbon chains rather than an artificial HOMO-LUMO electron displacement within a molecular orbital framework. The model reproduces ab initio and experimental data well, including the energy of the photo excited state, and with finer tuning may reproduce the 11-cis to all-trans isomerization of retinal, and may help explain the electronic mechanism of this peculiarly fast and efficient process.