Synthesis and properties of [8]-, [10]-, [12]-, and [16]cyclo-1,4-naphthylenes.

The synthesis and properties of various []cyclo-1,4-naphthylenes ([]CNs, = 8, 10, 12, and 16) are described. Initially, extended L-shaped units, which could be converted into quater- or quinquenaphthylenes were prepared. Nickel- or palladium-mediated couplings of these extended L-shaped units, followed by reductive aromatization of the coupling products afforded [8]-, [10]-, [12]-, and [16]CNs. The size-dependent photophysical properties of these CNs were confirmed by measuring their UV-vis absorption and fluorescence spectra. The theoretical studies supported substantial effects of the number of naphthalene rings on the structural and photophysical properties of these CNs. A kinetic study on the thermal conversion of the -symmetric conformer of [10]CN into its most stable -symmetric conformer indicated that ring strain affects the rotation barrier of the naphthalene rings in [10]CN.