title: Excited state intramolecular proton transfer in π-expanded phenazine-derived phenols.
abstract: Two previously inaccessible analogs of 10-hydroxybenzo[h]quinoline were prepared via a straightforward strategy comprising the formation of π-expanded phenazines skeleton followed by C-H acetoxylation at position 10. Two bis-phenols possessing C2 and D2 symmetry were obtained in yields of 52% and 15%, respectively. The occurrence of excited state intramolecular proton transfer (ESIPT) was detected in all cases because steady state emission was observed only from the excited keto-tautomer. Additionally, a short-lived, ∼0.1 ps, emission decay was resolved by the femtosecond up-conversion technique at the blue side of the keto-tautomer emission band, 610 nm, and was attributed to the ESIPT, i.e., conversion from enol to keto tautomer. In comparison with the corresponding 10-hydroxybenzo[h]quinoline emissions, the emission spectrum of the π-expanded phenazine analogues were weaker but displayed a characteristic bathochromically shift into NIR region. These phenazine analogues constitute one of largest heterocycles for which ESIPT was unambiguously detected.
authors.affiliation: Institute of Organic Chemistry of the Polish Academy of Sciences , 01-224 Warsaw, Poland.
authors.forename: Joanna
authors.initials: J
authors.lastname: Piechowska
authors.forename: Kirsi
authors.initials: K
authors.lastname: Virkki
authors.forename: Bartłomiej
authors.initials: B
authors.lastname: Sadowski
authors.forename: Helge
authors.initials: H
authors.lastname: Lemmetyinen
authors.forename: Nikolai V
authors.initials: NV
authors.lastname: Tkachenko
authors.forename: Daniel T
authors.initials: DT
authors.lastname: Gryko