Shedding new light on an old molecule: quinophthalone displays uncommon N-to-O excited state intramolecular proton transfer (ESIPT) between photobases

  • Sci Rep. 2017 Jun 20;7(1):3863. doi: 10.1038/s41598-017-04114-9.
Gi Rim Han  1 ,  Doyk Hwang  2 ,  Seunghoon Lee  1 ,  Jong Woo Lee  1 ,  Eunhak Lim  1 ,  Jiyoung Heo  3 ,  Seong Keun Kim  4  5
Affiliations
  • 1. Seoul National University, Department of Chemistry, Seoul, 08826, Republic of Korea.
  • 2. Seoul National University, Department of Biophysics and Chemical Biology, Seoul, 08826, Republic of Korea.
  • 3. Sangmyung University, Department of Biomedical Technology, Chungnam, 31066, Republic of Korea.
  • 4. Seoul National University, Department of Chemistry, Seoul, 08826, Republic of Korea. [email protected].
  • 5. Seoul National University, Department of Biophysics and Chemical Biology, Seoul, 08826, Republic of Korea. [email protected].
PMID: 28634405 DOI: 10.1038/s41598-017-04114-9
Abstract

Excited state dynamics of common yellow dye quinophthalone (QPH) was probed by femtosecond transient absorption spectroscopy. Multi-exponential decay of the excited state and significant change of rate constants upon deuterium substitution indicate that uncommon nitrogen-to-oxygen excited state intramolecular proton transfer (ESIPT) occurs. By performing density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations, we found that adiabatic surface crossing between the S1 and S2 states takes place in the photoreaction. Unlike most cases of ESIPT, QPH does not exhibit tautomer emission, possibly due to internal conversion or back-proton transfer. The ESIPT of QPH presents a highly interesting case also because the moieties participating in ESIPT, quinoline and aromatic carbonyl, are both traditionally considered as photobases.

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