Photochemical synthesis and electronic spectra of fulminene ([6]phenacene)

摘要

Facile synthesis of fulminene ([6]phenacene) was achieved through the Mallory reaction of 1-(1-naphthyl)-2-(1-phenanthryl)ethene or the 9-fluorenone-sensitized photo-ring-closure of 1-(1-naphthyl)-2-(1-phenanthryl) ethane. The electronic spectral properties of fulminene were investigated for the first time using photoluminescence as well as transient absorption spectroscopy. The spectral features were compared with those of a series of lower phenacene homologs such as phenanthrene ([3]phenacene), chrysene ([4]phenacene), and picene ([5]phenacene). For the [n]phenacene series, both the fluorescence and phosphorescence bands linearly red-shifted with an increase in the number of the benzene rings (n). Trends in the energy levels of the excited singlet (E_S) and the triplet (E_T) states were expressed as E_s = -2.6n + 89.1 (kcal mol~(-1)) and E_T = -1.8n + 66.2 (kcal mol~(-1)), respectively. In the case of fulminene, laser flash photolysis displayed a transient spectrum with an absorption maximum (λ_(max) ~(T-T)) at 675 nm, which was assigned as the triplet fulminene excited state. The λ_(max) ~(T-T) values for the [n]phenacene series showed a linear correlation as a function of the ring number n, given by an equation, λ_(max) ~(T-T) = 60n + 318 (nm).