Synthesis and properties of -, -, -, and cyclo-1,4-naphthylenes†
The synthesis and properties of various [n]cyclo-1,4-naphthylenes ([n]CNs, n = 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 -, -, -, and 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 Cs-symmetric conformer of CN into its most stable D5d-symmetric conformer indicated that ring strain affects the rotation barrier of the naphthalene rings in CN.