Development of New Computational Approaches to Predict the UV-Vis Behavior of Charge Transfer Organic Dyes and Application to Novel Silole Containing Dyes

Author

George Hudson, Southern Illinois University CarbondaleFollow

Date of Award

12-1-2012

Degree Name

Doctor of Philosophy

Department

Chemistry

First Advisor

Wang, Lichang

Abstract

Dye sensitized solar cells (DSC's) have received much attention since their invention in 1991. These solar cells are cheap to manufacture, durable, and use low toxicity components. Dyes used for DSC's often exhibit charge transfer character upon absorption of light. Predicting dye behavior in charge transfer cases has been difficult using the current computational methods and an accurate method is needed. Presented here are two methods to improve the accuracy of time-dependent density functional theory (TD-DFT) predictions regarding the UV-Vis absorbance of organic dyes. This work also presents the study of three new dyes that incorporate a novel functionality into their structure using the new computational methods. The first improved method was to use orbital overlap to incorporate higher energy orbitals into the TD-DFT predictions. This was done by considering half the energy difference between the unoccupied orbital predicted by TD-DFT and a higher energy unoccupied orbital that overlaps with the occupied orbital predicted by TD-DFT. This method was used to predict the UV-Vis absorbance spectra of one previously synthesized dye and two novel dyes that incorporate a silole ring into their structure. The silole ring has been used for chromophoric polymers and has been used in fused ring system containing dyes but has yet to be used as an individual entity in dye structure. This work shows that the incorporation of the silole ring causes a red shift in the absorbance and in the dyes studied offers an absorbance spectrum that more closely aligns with the solar spectrum. The second computational approach presented is to use TD-DFT to determine the donor portion of the organic dye and then consider the donor to be the light absorbing entity. TD-DFT calculations are then performed on the donor portion which yields a predicted absorbance that is in better agreement with the experimental value. This approach was used on several dyes with good results and was also used on a third novel dye that incorporated the silole moiety. According to the results the novel dye was predicted to have an absorbance maximum within 2 nm of the wavelength of maximum incident from solar radiation.