The solvatochromic test results to verify their HLCT characters are shown in Fig. , &d. When changing the solvent from low-polar hexane to the high-polar acetonitrile, the UV-vis absorption spectra (Supplementary Fig. ) of the three HLCT emitters remain virtually unchanged in terms of shape and position. This infers that the groundstate dipole moment of the molecule is slightly affected by the solvent variation. In contrast, the PL spectrum (Fig. ) of BTD-HeBr, for example, showed red-shifts by .