Evidence of homolytic and heterolytic pathways in the photodissociation of iminosulfonates and direct detection of the p-toluenesulfonyloxyl radical

Abstract

The mechanistic aspects of the photochemistry of several iminosulfonate photoacid generators (PAGs) have been studied based on product analysis, nanosecond laser flash photolysis, and determination of acid generation efficiencies. Our findings support a competition between homolytic and heterolytic N-O dissociation mechanisms. By measuring the efficiencies of acid generation for each PAG in the presence and absence of an ion quencher, we were able to roughly quantify the degree of branching between heterolytic and homolytic photocleavage pathways for each PAG. The p-toluenesulfonyloxyl radical was detected upon laser flash photolysis of several PAGs and was found to have a lambda(max) at 540 nm. By quenching the 540 nm transient with a variety of reactive species, the rate constants for reaction of the p-toluenesulfonyloxyl radical with these substrates were determined. The p-toluenesulfonyloxyl radical is shown to be a highly reactive species, which undergoes rapid hydrogen transfer and is a powerful oxidizer.

The Methylsulfonyloxyl Radical, CH3SO3

“…A transient structureless absorption band at λ max ≈450 nm with a lifetime of 7–20 μs was assigned to this radical, and its photoinduced ( λ max =480 nm) dissociation into CH 3 and SO 3 was proposed 7. A similar transient absorption band was also observed for the putative p ‐toluenesulfonyloxyl radical ( λ max =540 nm) in CH 3 CN solution during laser ( λ =266 nm) photolysis of iminosulfonates 8. The formation of CH 3 SO 3 was reported by electron beam irradiation (3 MeV) of the CH 3 SO 3 − ion in ionic liquids at 77 K,9 and very recently by the reaction of methylsulfinyl radicals (CH 3 SO) and molecular oxygen ( 3 O 2 ) in solid argon 10…”

“…[7] As imilar transient absorption band was also observed for the putative p-toluenesulfonyloxyl radical (l max = 540 nm) in CH 3 CN solution during laser (l = 266 nm) photolysis of iminosulfonates. [8] Thef ormation of CH 3 SO 3 was reported by electron beam irradiation (3 MeV) of the CH 3 SO 3 À ion in ionic liquids at 77 K, [9] and very recently by the reaction of methylsulfinyl radicals (CH 3 SO) and molecular oxygen ( 3 O 2 )i ns olid argon. [10] Themolecular structures and the thermodynamic properties of CH 3 SO 3 and various isomers have been calculated at different theoretical levels.…”

Two-photon lithography in visible and NIR ranges using multibranched-based sensitizers for efficient acid generation

“…They constitute an important class of cationic photoinitiators which have a strategic position in the polymer industries 14,15 . Commercially available PAGs are mainly photoactivated through direct excitation at wavelengths ranging from VUV to close UV [16][17][18][19][20][21][22] . Moreover they exhibit very low 2PA crosssections because of their limited -conjugation 23 .…”

1-Acetylferroceneoxime-based photoacid generators: application towards sol–gel transformation and development of photoresponsive polymer for controlled wettability and patterned surfaces

“…Based on the mechanistic studies as reported by Scaiano and his coworkers 27 and Shirai et al 28 for the photolysis of oxime sulfonates and from our solvent investigation, we proposed the possible mechanism for the photogeneration of acids. On excitation, both the carboxylates and sulfonates of 1-acetylferroceneoxime (3a-d and 4a-d) undergo homolytic N-O bond cleavage from the singlet excited state to generate an iminyl and acyloxy or sulfonyl radical pair (Scheme 3).…”