title: Fast Singlet Exciton Decay in Push-Pull Molecules Containing Oxidized Thiophenes.
abstract: A common synthetic strategy used to design low-bandgap organic semiconductors employs the use of "push-pull" building blocks, where electron -rich and electron-deficient monomers are alternated along the π-conjugated backbone of a molecule or polymer. Incorporating strong "pull" units with high electron affinity is a means to further decrease the optical gap for infrared optoelectronics or to develop n-type semiconducting materials. Here we show that the use of thiophene-1,1-dioxide as a strong acceptor in "push-pull" oligomers affects the electronic structure and carrier dynamics in unexpected ways. Critically, the overall excited-state lifetime is reduced by several orders of magnitude relative to unoxidized analogs due to the introduction of low-energy optically dark states and low-energy triplet states that allow for fast internal conversion and intramolecular singlet fission. We found that the electronic structure and excited-state lifetime are strongly dependent on the number of sequential thiophene-1,1-dioxide units. These results suggest that both the static and dynamical optical properties are highly tunable via small changes in chemical structure that have drastic effects on the optoelectronic properties, which can impact the types of applications that involve these materials.
authors: †Department of Chemistry, Columbia University, 3000 Broadway, New York, New York 10027, United States.|‡Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973, United States.
authors: Erik
authors: E
authors: Busby
authors: †Department of Chemistry, Columbia University, 3000 Broadway, New York, New York 10027, United States.
authors: Jianlong
authors: J
authors: Xia
authors: †Department of Chemistry, Columbia University, 3000 Broadway, New York, New York 10027, United States.
authors: Jonathan Z
authors: JZ
authors: Low
authors: ‡Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973, United States.
authors: Qin
authors: Q
authors: Wu
authors: ‡Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973, United States.|§Condensed Matter Physics and Materials Science, Brookhaven National Laboratory, Upton, New York 11973, United States.
authors: Jessica
authors: J
authors: Hoy
authors: †Department of Chemistry, Columbia University, 3000 Broadway, New York, New York 10027, United States.
authors: Luis M
authors: LM
authors: Campos
authors: ‡Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973, United States.
authors: Matthew Y
authors: MY
authors: Sfeir