title: Effect of Selenium Substitution on Intersystem Crossing in π-Conjugated Donor-Acceptor-Donor Chromophores: The LUMO Matters the Most.
abstract: This study explores the effect of substitution of selenium (Se) for sulfur (S) on the photophysical properties of a series of π-conjugated donor-acceptor-donor chromophores based on 4,7-bis(2-thienyl)-2,1,3-benzothiadiazole (TBT). The effect of Se substitution is studied systematically, where the substitution is in the thiophene donors only, the benzothiadiazole acceptor only, and in all of the positions. The fluorescence quantum yield decreases with an increase in Se substitution. Nanosecond-microsecond transient absorption and singlet oxygen sensitization experiments show that the effect of Se is due to an increase in the rate and efficiency of intersystem crossing with increased Se substitution. The relationship between intersystem crossing efficiency and heteroatom substitution pattern shows that the effects are largest when the heavy atom Se is in the acceptor benzothiadiazole unit. DFT calculations support the hypothesis that the effect arises because the LUMO is concentrated in the acceptor moiety, enhancing the spin-orbit coupling effect imparted by the Se atom.
authors.affiliation: Department of Chemistry and Center for Macromolecular Science and Engineering, University of Florida , Gainesville, Florida 32611-7200, United States.
authors.forename: Rajendra
authors.initials: R
authors.lastname: Acharya
authors.affiliation: Department of Chemistry and Center for Macromolecular Science and Engineering, University of Florida , Gainesville, Florida 32611-7200, United States.
authors.forename: Seda
authors.initials: S
authors.lastname: Cekli
authors.affiliation: Department of Chemistry and Center for Macromolecular Science and Engineering, University of Florida , Gainesville, Florida 32611-7200, United States.
authors.forename: Charles J
authors.initials: CJ
authors.lastname: Zeman
authors.affiliation: Petrochemicals Research Institute, King Abdulaziz City for Science and Technology , Riyadh 11442, Kingdom of Saudi Arabia.
authors.forename: Rashid M
authors.initials: RM
authors.lastname: Altamimi
authors.affiliation: Department of Chemistry and Center for Macromolecular Science and Engineering, University of Florida , Gainesville, Florida 32611-7200, United States.
authors.forename: Kirk S
authors.initials: KS
authors.lastname: Schanze
mesh_terms: D005453:Fluorescence; D011789:Quantum Theory; D012643:Selenium / Q000737:chemistry*
chemical_list: D012643:Selenium