Visible-Light-Induced Heptacene Generation Under Ambient Conditions: Utilization Of Single-Crystal Interior As An Isolated Reaction Site

The photo-induced generation of unstable molecules generally requires stringent conditions to prevent oxidation and the concomitant decomposition of the products. The visible-light-induced conversion of two heptacene precursors to heptacene was studied. Single crystals of bis- and mono-alpha-diketone-type heptacene precursors (7-DK2and7-DK1, respectively), were prepared to investigate the effect of precursor structure on reactivity. The photoirradiation of a7-DK2single crystal cleaved only one alpha-diketone group, forming an intermediate bearing a pentacene subunit, while that of a7-DK1single crystal gave rise to characteristic absorption peaks of heptacene and their increase in intensity with photoirradiation time, indicating the generation of heptacene without decomposition. Heptacene production was not observed when the precursors were photoirradiated in solution, implying that the single crystal interior provided isolation from the external environment, thus preventing heptacene oxidation.