Elucidating complex triplet-state dynamics in the model system isopropylthioxanthone
Nikolaos Liaros,
Sandra A. Gutierrez Razo,
Matthew D. Thum,
Hannah M. Ogden,
Andrea N. Zeppuhar,
Steven Wolf,
Tommaso Baldacchini,
Matthew J. Kelley,
John S. Petersen,
Daniel E. Falvey,
Amy S. Mullin,
John T. Fourkas
Affiliations
Nikolaos Liaros
Department of Chemistry & Biochemistry, University of Maryland, College Park, MD 20742, USA
Sandra A. Gutierrez Razo
Department of Chemistry & Biochemistry, University of Maryland, College Park, MD 20742, USA
Matthew D. Thum
Department of Chemistry & Biochemistry, University of Maryland, College Park, MD 20742, USA
Hannah M. Ogden
Department of Chemistry & Biochemistry, University of Maryland, College Park, MD 20742, USA
Andrea N. Zeppuhar
Department of Chemistry & Biochemistry, University of Maryland, College Park, MD 20742, USA
Steven Wolf
Department of Chemistry & Biochemistry, University of Maryland, College Park, MD 20742, USA
Tommaso Baldacchini
Newport Corporation, 1791 Deere Avenue, Irvine, CA 92606, USA
Matthew J. Kelley
Newport Corporation, 1791 Deere Avenue, Irvine, CA 92606, USA
John S. Petersen
Department of Chemistry & Biochemistry, University of Maryland, College Park, MD 20742, USA; imec, Kapeldreef 75, 3001 Leuven, Belgium
Daniel E. Falvey
Department of Chemistry & Biochemistry, University of Maryland, College Park, MD 20742, USA
Amy S. Mullin
Department of Chemistry & Biochemistry, University of Maryland, College Park, MD 20742, USA
John T. Fourkas
Department of Chemistry & Biochemistry, University of Maryland, College Park, MD 20742, USA; Institute for Physical Science & Technology, University of Maryland, College Park, MD 20742, USA; Maryland Quantum Materials Center, University of Maryland, College Park, MD 20742, USA; Maryland NanoCenter, University of Maryland, College Park, MD 20742, USA; Corresponding author
Summary: We introduce techniques for probing the dynamics of triplet states. We employ these tools, along with conventional techniques, to develop a detailed understanding of a complex chemical system: a negative-tone, radical photoresist for multiphoton absorption polymerization in which isopropylthioxanthone (ITX) is the photoinitiator. This work reveals that the same color of light used for the 2-photon excitation of ITX, leading to population of the triplet manifold through intersystem crossing, also depletes this triplet population via linear absorption followed by reverse intersystem crossing (RISC). Using spectroscopic tools and kinetic modeling, we identify the reactive triplet state and a non-reactive reservoir triplet state. We present compelling evidence that the deactivation channel involves RISC from an excited triplet state to a highly vibrationally excited level of the electronic ground state. The work described here offers the enticing possibility of understanding, and ultimately controlling, the photochemistry and photophysics of a broad range of triplet processes.
