In toluene solutions, CCO-1, CCO-2 and CCO-3 show almost identical absorption profiles with absorption maxima at 364 nm, associated with the π-π* transitions, which are obviously red-shifted in comparison with that of CBP-1 due to the expansion of molecular conjugation (Fig. ). Apparent absorption tails are observed between 380 and 430 nm stemming from transitions from SXAC donor to CCO-α acceptor. The intensities of the absorption tails of CCO-1, CCO-2 and CCO-3 are stronger than that of CBP-1, suggesting they have larger f values, consistent with the theoretical calculation results. The PL spectra of CCO-1, CCO-2 and CCO-3 have peaks at about 465 nm and full width at half maximum (FWHM) of 69 nm, which are blue-shifted by 10 nm and narrowed by 13 nm, respectively, compared with those of CBP-1. In different polar solvents, such as tetrahydrofuran, dichloromethane and acetonitrile, CCO-1 shows smaller red-shifts in PL spectra than CBP-1, validating its weaker D-A interaction (Supplementary Fig. ). The ΦPLs of CCO-1, CCO-2 and CCO-3 in toluene solutions are 70%, 72% and 69%, respectively, much higher than that of CBP-1 (25%), evidencing the enhanced rigidity of CCO-α has successfully reduced molecular motion and lowered nonradiative energy dissipation.