SCPP [8] molecule is calculated to has exceptionally high strain energy up to 127 kcal/mol at the B3LYP/6-31G(d) level (Figure ). This bismacrocycle molecule is highly strained, and its ring strain is even much larger than the very small nanoring [5]CPP (119 kcal/mol). We concluded that the structural factors contribute to the unexpectedly large strain energy in SCPP [8]. Compared with the individual phenylene, the central benzene bridged by two carbon nanorings has much larger resistance to twisting. In addition, the limited conformational freedom in SCPP [8] leads to significant multiple repulsive interactions between adjacent phenylene fragments. The geometrical optimization results indicated that SCPP [8] features chiral C2 symmetry, and the twist angle in the bridging phenyl is ~19.55 o . The frontier molecular orbitals of [8]CPP and SCPP [8] are shown in Figures and, respectively. The energy levels of the occupied molecular orbitals of SCPP[8] move to higher positions than those of [8]CPP, while the unoccupied molecular orbitals move to lower positions than those of [8]CPP. Therefore, the SCPP[8] achieves a smaller HOMO-LUMO gap of ~2.780 eV compared to [8]CPP. The photophysical properties of SCPP [8] were further studied by UV-Vis absorption spectroscopy, fluorescence spectroscopy, and time-resolved fluorescence decay (Figure ). A single macrocyclic [8]CPP was used as a reference compound for comparison. The lower symmetry of SCPP[8] (C2) in comparison with the circular CPPs (D2) results in a more complex pattern of electronic transitions, as determined in time-dependent density functional theory (TD-DFT) calculations. The absorption band of SCPP [8] was in the region between 265 and 436 nm, and the maximum absorption peak (λmax) appears at 368 nm (Figure ). The extinction coefficients reach up to 1.22 × 10 5 M -1 • cm -1 . To identify the difference of optical properties, density functional theory calculations were performed by using Gaussian 16 software. In accordance with the aforementioned decrease in the HOMO-LUMO gap, the absorption spectrum of SCPP [8] showed an obvious redshift compared with [8]CPP. Based on the calculated results, an excellent correlation between the calculated and experimental absorption spectra was observed. The three main absorption peaks can be attributed to the transition of HOMO-2 → LUMO for the peak at 368 nm, HOMO → LUMO+2 for the peak at 346 nm, and HOMO-1 → LUMO+5 for the peak at 305 nm. In addition, the observed absorption peak of [8]CPP at 340 nm can be assigned to the transition of HOMO-1 → LUMO and HOMO → LUMO+1. The redshift effect of the absorption spectrum in SCPP[8] compared to [8]CPP was ascribed to the shift of the frontier molecular orbitals.