title: Tuning the optical properties of ZnTPP using carbonyl ring fusion.
abstract: Zinc meso-tetraphenylporphyrin (ZnTPP) was modified in such a way to allow the effect of an asymmetric structural distortion on its optical properties to be investigated. This involved the fusion of a phenyl group to an adjacent pyrrole ring via a carbonyl bridge. With the aid of Density Functional Theory (DFT) and time-dependent DFT (TD-DFT) calculations it was found that the asymmetric distortion away from planarity induced by the carbonyl fusion resulted in a loss of degeneracy in the two lowest unoccupied molecular orbitals (LUMOs). The effect was a red shift of the electronic absorbance bands, an increased Q:B ratio from 0.046 in ZnTPP to 0.096 in the fused derivative, and the appearance of additional UV-vis peaks. This study therefore suggests that structural distortions, as well as electronic substituents may be used to alter absorbance spectra, a technique which is of interest in the design of light-harvesting dyes.
authors.affiliation: Department of Chemistry and MacDiarmid Institute for Advanced Materials and Nanotechnology, University of Otago, PO Box 56, Dunedin, New Zealand.
authors.forename: Deidre M
authors.initials: DM
authors.lastname: Cleland
authors.forename: Keith C
authors.initials: KC
authors.lastname: Gordon
authors.forename: David L
authors.initials: DL
authors.lastname: Officer
authors.forename: Pawel
authors.initials: P
authors.lastname: Wagner
authors.forename: Penny J
authors.initials: PJ
authors.lastname: Walsh
mesh_terms: D008665:Metalloporphyrins / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D011789:Quantum Theory; D013056:Spectrophotometry, Ultraviolet
chemical_list: D008665:Metalloporphyrins; C048955:zinc tetraphenylporphyrin