Zheng Shi, Ping Peng, Daniel Strohecker, and Yi Liao* J. Am. Chem. Soc., 2011, 133, 14699-14703 Long-Lived Photoacid Based upon a Photochromic Reaction Zheng Shi, Ping Peng, Daniel Strohecker, and Yi Liao* Department of Chemistry, University of Central Florida, Orlando, Florida 32816, United States

(Photoinduced) Proton Transfer (Photosynthetic Process) O. A. Sytina et al., Nature, 2008, 456, 1001.

Photoacid Generators (PAGs) Photocleavage + Hydrogen abstraction Proton-transfer + Acid generation Irreversible process *pH jump by photoexciation (grand state) (excited state) hn pKa = 9.2 pKa = 2.0 Reversible process Short lifetime of excited state

Photocontrol of Molecular and Supramolecular Events *Control of complex formation *H2 generation J. L. Dempsey et al., JACS, 2010, 132, 16774. *Locking of photoreactivity M. Ohsumi et al., Chem. Commun., 2005, 3921. S. Silvi et al., JACS, 2007, 129, 13378.

Photochromic Reaction of Spirobenzopyran Vis. UV MEH SP (in polar solvent) Stable form; MEH (in non-polar solvent) Stable form; SP 5.88 × 10-4 M (water)

Photoswitching of pH Value 5.88 × 10-4 M (water)

Lifetime of the Proton Dissociation-state First order kinetics k = 0.00914 s-1 t1/2 = 0.693/k = 76 s Long-lived proton-dissociation state

Substituent Dependence (MEH) pH = 4.9 less reactivity low solubility (SP) pH = 3.9 DpH ~ 1.0

Photoinduced Catalyzing Property (3.1 mM) (12.5 mM) (419 nm + 570 nm) (Yield of Ethyl acetate) 1: 33 % (1h), 50 % (2h), 66 % (3h), 0 % (dark) 2: 0 % (3h)

Photoinduced the Volume Change of Hydrogel (Before) (After) Vis. A copolymer of poly(acrylic acid) and polyacrylamide “Shrink” (~ 1/8 volume)

Conclusions Ex. 1) (Before) (After) Vis. Ex. 2) pH ~ 5.5 pH ~ 3.5 “Shrink” (~ 1/8 volume)