Mechanism of Reaction and Photoacid Generation of N-Oxysuccinimidoarylsulfonate PAGs:  A Laser Flash Photolytic Study

Abstract

The photochemical behavior of four N-oxysuccinimidoarylsulfonate photoacid generators (PAGs), 1-[[phenylsulfonyl]oxy]-(PSPD), 1-[[(4-methylphenyl)sulfonyl]oxy]-(MSPD), 1-[[(4-fluorophenyl)sulfonyl]oxy]-(FSPD), 1-[[ (4-chlorophenyl)sulfonyl]oxy]-2,5-pyrrolidinedione (CSPD), has been studied by means of nanosecond laser flash photolysis (λ exc ) 266 nm) and steady-state photolysis (λ exc ) 254 nm) with the aim of understanding the reaction mechanism and, particularly, photoacid generation pathways and efficiency in the deep UV region. Upon photoexcitation, the formation of arylsulfonyl radicals and their subsequent desulfonylation were detected for the four PAGs. In oxygen-saturated solution, the generation of the corresponding arylperoxy radicals was also observed. Photoacid generation quantum yields upon laser excitation were found to range from 0.04 to 0.05. Product studies following steady-state irradiations reveal that acid generation is dominated by the formation of sulfonic acids.

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 .…”

Photoimaging and Lithographic Processes in Polymers

“…Using laser flash photolysis, they elucidated the mechanism of photolysis and acid formation following direct irradiation as well as sensitization with Xanthone for the first two PAGs on the left column of Chart 12.3 [27,28]. Following absorption of a photon during direct excitation, the next step is homolytic cleavage, yielding arylsulfonyl radical and a nitrogencentered radical.…”

Efficient Self‐Contained Photoacid Generator System Based on Photochromic Terarylenes

“…Some applications demand the generation of sufficiently strong acids, for example, photopolymerization initiations. Two types of PAGs are currently used: ionic and nonionic . A large number of onium‐salt‐based ionic PAGs such as aryldiazonium, diaryliodonium, triarylsulfonium, and triarylphosphonium salts have been used at the forefront of industry for more than three decades and their photochemistry has been investigated in great detail .…”

“…Twot ypes of PAGs are currently used:i onic [14] and nonionic. [15] Al arge number of onium-salt-based ionic PAGs such as aryldiazonium,d iaryliodonium, triarylsulfonium, and triarylphosphonium salts have been used at the forefront of industry for more than three decades and their photochemistry has been investigatedin great detail. [16] Meanwhile, nonionicP AGs are exemplified by N-oxyimidosulfonates, whichp roduce sul-fonic acids.…”

“…[16] Meanwhile, nonionicP AGs are exemplified by N-oxyimidosulfonates, whichp roduce sul-fonic acids. [15,17] More recently,t he chemicalm odificationso f ionic PAGs [18][19][20] and the combinations of sensitizers and nonionic PAGs [21] sensitized them to two-photon activation.B oth the onium salt and nonionic PAGs dominantly undergo homolytic bond-cleavage reactionsu pon light irradiation (Scheme 1a and b). Photogenerated radicalspeciesneed to extract ahydrogena tom from solvent molecules or other hydrogen sources (RH) to generateaBrønsted acid, which gives rise to medium-dependent sensitivity and complicated fragments remaining in the systems.…”