title: Optimization in solvent selection for chlorin e6 in photodynamic therapy.
abstract: The photophysical properties of chlorin e6 (Ce6) in twelve different protic, aprotic and non-polar solvents were investigated using ultraviolet-visible and fluorescence spectroscopic methods. Solvatochromic effects were determined by the changes in quantum yield, Stokes shift, fluorescence half-life and excited state dipole moments of Ce6 in the different solvents. The absorption shifts observed in different solvents were further analyzed using the Kamlet-Abboud-Taft model and the nature of solute-solvent interactions between Ce6 and different protic and aprotic solvents was elucidated. The quantum yields were found highest in protic solvents (except water), followed by aprotic and non-polar solvents. Solvent polarity parameters showed a linear increasing trend with Stokes shift and fluorescence half-life, which indicated the presence of Ce6-solvent interaction. Using the Kamlet-Abboud-Taft model, a direct correlation between the solvent polarity parameters and absorption shift was observed, which substantiated the existence of Ce6-solvent interaction by hydrogen bond formation. The excited state dipole moments in specific protic and aprotic solvents were found to be higher than the ground state dipole moments, implying a more polar nature of Ce6 during excited state transition.
authors.affiliation: Department of Pharmacy, Faculty of Science, National University of Singapore, 18 Science Drive 4, Singapore 117543, Singapore.
authors.forename: Shubhajit
authors.initials: S
authors.lastname: Paul
authors.forename: Paul Wan Sia
authors.initials: PW
authors.lastname: Heng
authors.forename: Lai Wah
authors.initials: LW
authors.lastname: Chan
mesh_terms: D002735:Chlorophyllides; D006207:Half-Life; D010778:Photochemotherapy; D011166:Porphyrins / Q000032:analysis*; D012997:Solvents / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet
chemical_list: D002735:Chlorophyllides; D011166:Porphyrins; D012997:Solvents; C062985:phytochlorin