Excited state intramolecular hydrogen atom transfer of phenylethynyl- substituted 2'-hydroxychalcones

摘要

(E)-1-[2-Hydroxy-4-(phenylethynyl)phenyl]-3-[4-(phenylethynyl)phenyl] prop-2-en-1-one (1), (E)-1-[2-hydroxy-4-(phenylethynyl)phenyl]-3-phenylprop-2- en-1-one (2), and (E)-1-(2-hydroxyphenyl)-3-[4-(phenylethynyl)phenyl]prop-2-en- 1-one (3), which belong to a new class of 2'-hydroxychalcones with phenylethynyl group(s) at the para position of the phenyl ring, were synthesized, and their photochemical properties were investigated. The lowest energy absorption band of 1 peaks at a longer wavelength (383 nm) with a much larger molar extinction coefficient (5.0 × 10~4 M~(-1) cm~(-1)) than that of the parent 2'-hydroxychalcone (2'HC) (2.0 × 10~4 M~(-1) cm~(-1) at 318 nm). Upon photoexcitation, all three compounds underwent excited-state intramolecular hydrogen atom transfer (ESIHT) to produce an excited tautomer that emitted fluorescence with a large Stokes shift in the longer wavelength region at 600-700 nm. The quantum yield of the tautomer fluorescence of 1 was not high at 298 K (Φ_f = 9.1 × 10~(-5)), but was highest among 2'HC and its analogues. The Φ f values of 1-3 increased 10-30 fold upon reducing the temperature from 298 to 77 K.