Precise synthesis and photophysical properties of a small chiral carbon nanotube segment: cyclo[7]paraphenylene-2,6-naphthylene.

Herein we report the precise synthesis and photophysical properties of a naphthalene-containing carbon nanohoop, cyclo[7]paraphenylene-2,6-naphthylene ([7]CPPNa2,6), as a sidewall segment of a [9,8] single-walled carbon nanotube ([9,8]SWNT) using a rationally designed strategy. To the best of our knowledge, [7]CPPNa2,6 represents the smallest chiral SWNT segment ever reported. The structure was confirmed by 1H NMR, 2D 1H-1H COSY NMR, 13C NMR, and HR-MS spectrometry. The nanohoop's interesting photophysical properties were investigated by steady-state and time-resolved spectroscopy combined with theoretical calculations. Compared with the [8]CPP and [9]CPP nanohoops, [7]CPPNa2,6 has a moderate strain energy (89.6 kcal mol-1) and a higher HOMO-LUMO gap (3.5 eV).