Electronic
Relaxation Pathways in Heavy-Atom-Free
Photosensitizers Absorbing Near-Infrared Radiation and Exhibiting
High Yields of Singlet Oxygen Generation
posted on 2021-02-15, 21:14authored byLuis A. Ortiz-Rodríguez, Sean J. Hoehn, Axel Loredo, Lushun Wang, Han Xiao, Carlos E. Crespo-Hernández
Heavy-atom-free photosensitizers
(HAF-PSs) based on thionation
of carbonyl groups of readily accessible organic compounds are rapidly
emerging as a versatile class of molecules. However, their photochemical
properties and electronic relaxation mechanisms are currently unknown.
Investigating the excited-state dynamics is essential to understand
their benefits and limitations and to develop photosensitizers with
improved photochemical properties. Herein, the photochemical and electronic-structure
properties of two of the most promising HAF-PSs developed to date
are revealed. It is shown that excitation of thio-4-(dimethylamino)naphthalamide
and thionated Nile Red with near-infrared radiation leads to the efficient
population of the triplet manifold through multiple relaxation pathways
in hundreds of femtoseconds. The strong singlet–triplet couplings
in this family of photosensitizers should enable a broad range of
applications, including in photodynamic therapy, photocatalysis, photovoltaics,
organic LEDs, and photon up-conversion.