State Dependent Photochemical and Photophysical Behavior of Dithiolate Ester and Trithiocarbonate RAFT Polymerization Agents.

23 March 2020, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


The rise in popularity of photochemically initiated RAFT polymerization (photoRAFT) along with the broad spectrum of proposed, and possible, initiation mechanisms results in the need for careful characterization of the photophysical properties of some common RAFT agents. Direct irradiation of the RAFT agent as a means to generate radicals, also known as the photoiniferter mechanism, is one commonly proposed mechanism. The current study shows that the dithioesters and trithiocarbonates have lowest singlet, and triplet excited state energy levels that are close to, or lower then C-S bond dissociation energies. Excitation of these agents into their S1 band results in negligible radical production, while excitation into S2 or higher results in the decomposition of dithioesters and trithiocarbonates resulting in radical formation, but with low quantum yields. Likewise, there is significant literature precedence for an electron transfer initiation mechanism, PET-RAFT. It is shown that the dithioesters and trithiocarbonates all show peak reduction potentials at ca. -1.0 V (vs. SCE). However, transient absorption spectroscopy studies of the electron transfer from a mediator shows that theses reactions occur rapidly only when the mediator potential is more negative than -1.2 V (vs. SCE).


RAFT chemistry
radical chemistry
laser flash photolysis
Quantum Yields Photodegradation
Dithiolate esters
photoinduced electron transfer process
triplet energy transfer
Bond Dissociation Enthalpies
DFT Calculations


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