Synthesis, Structure, and Photophysical Properties of -Phenylene-Embedded Cycloparaphenylene Nanorings.

Five -phenylene-embedded cycloparaphenylenes [9]CPP - were synthesized by the platinum-mediated cyclooligomerization strategy with high overall yields. The structures of [9]CPP - were determined by X-ray diffraction analysis. Compared to [9]CPP, [9]CPP caused a significant blueshift in the UV-vis absorption and fluorescence spectra. This result shows that the radial π-conjugation is distorted and partially interrupted. The photophysical properties of [9]CPP were further tuned by the introduction of various substituents for [9]CPP -. Methoxy group substitution at -phenylene did not change the photophysical properties significantly. Replacement of -phenylene by tetrafluoro-phenylene achieved a significant blueshift. When the carboxyl group was embedded at -phenylene or the methoxy group was embedded at -phenylene, significant redshifts were observed with blue color emission. Theoretical calculations revealed that the decrease in the HOMO-LUMO gap in [9]CPP and is favorable for the redshift of the fluorescence spectrum.