Photoacid

Photoacids are chemical compounds which release strong acids upon photolysis, which is useful in photolithography.[1]

An example is triphenylsulfonium triflate with the formula [(C6H5)3S][CF3SO3]. This colourless salt consists of a sulfonium cation and the triflate anion. Many related salts are known including those with other noncoordinating anions and those with diverse substituents on the phenyl rings.

The triphenylsulfonium salts absorb at 233 nm, which induces the series of reactions shown:[2]

[(C6H5)3S+][CF3SO3−] + hν → [(C6H5)2S+.][CF3SO3−] + C6H5.
[(C6H5)2S+.][CF3SO3−] + C6H5. → (C6H5C6H4)(C6H5)S + CF3SO3H

Another example of a photoacid is 8-hydroxy-1,3,6-pyrenetrisulfonate, known as HPTS.[3]

In a typical application, photoacids catalyze the polymerization of epoxides.

References

  1. ↑ J. V. Crivello "The Discovery and Development of Onium Salt Cationic Photoinitiators" Journal of Polymer Science: Part A: Polymer Chemistry, 1999, Volume 37, pp. 4241–4254. DOI CCC 0887-624X/99/234241-14.
  2. ↑ W. D. Hinsberg, G. M. Wallraff "Lithographic Resists" Kirk-Othmer Encyclopedia of Chemical Technology, Wiley-VCH, Weinheim, 2001. (Published online: 17 June, 2005)
  3. ↑ Amdursky N., Simkovitch R, and Huppert D. (1979) Excited-state proton transfer of photoacids adsorbed on biomaterials, J Phys Chem B. 118(48), pages 13859-69. doi:10.1021/jp509153r
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