Wydział Chemii

J. S. De Klerk

I. H. M. Van Stokkum

Anna Szemik-Hojniak

Irena Deperasińska

C. Gooijer

Hong Zhang

Wybren Jan Buma

F. Ariese

2010

Journal of Physical Chemistry A

114

4045-4050

10.1021/jp909468h

Naukowa

Angielski

Artykuł

Earlier steady-state fluorescence studies showed that 2-butylamino-6-methyl-4-nitropyridine N-oxide (2B6M) can undergo fast excited-state intramolecular proton transfer (ESIPT). In a nonpolar solvent such as n-octane, both normal and tautomeric fluorescence was observed. Strikingly, the relative ratio of those two emission bands and the fluorescence quantum yield of the normal emission were found to depend on the excitation wavelength in violation of the Kasha−Vavilov rule. In this work, the system was investigated further by means of transient absorption spectroscopy, followed by global and target analysis. Upon excitation at 420 nm, a normal excited singlet state S₁(N) is reached, which decays in about 12 ps via fluorescence and ESIPT (minor pathways) and to a long-lived “dark” state (major pathway) that is most probably the triplet T₁(N). Upon 330 nm excitation, however, a more complex pattern emerges and additional decay channels are opened. A set of four excited-state species is required to model the data, including a hot state S₁(N)* that decays in about 3 ps to the tautomer, to the long-lived “dark” state and to the relaxed S₁(N) state. A kinetic scheme is presented that can explain the observed transient absorption results as well as the earlier fluorescence data.

https://doi.org/10.1021/jp909468h

https://www.acs.org/content/acs/en.html