The ultraviolet-visible (UV-vis) absorption and photoluminescence (PL) properties of the four emitters were first investigated in toluene at room temperature (Error! Reference source not found.a). The absorption spectra of tDPABT1B and tDPABT2B show low-energy bands at 465 and 462 nm, with molar absorptivities, ε, of 55 ×10 3 and 54 ×10 3 M -1 cm -1 , respectively. The low-energy bands of tCzBT1B and tCzBT2B are bathochromically shifted at 472 nm (54 ×10 3 M -1 cm -1 ) and 471 nm (54 ×10 3 M -1 cm -1 ), respectively. These intense bands are attributed to a SRCT S0-S1 transition and are close to that of BTC-BNCz (labs of 473 nm, no e reported). The PL spectra of the four emitters are narrowband, peaking at λPL of 476 nm (FWHM: 23 nm, 0.11 eV) for tDPABT1B and tDPABT2B, and λPL of 489 nm (FWHM: 24 nm, 0.12 eV) for tCzBT1B and tCzBT2B, respectively. The PL spectra of the latter two are similar to that of BTC-BNCz (λPL of 488 nm, FWHM: 23 nm, 0.12 eV). The narrow FWHM and the small Stokes shifts (less than 17 nm) of the four emitters reflect their rigid structures (Figure ). There is a very small degree of positive solvatochromism (Figure ), which confirms that the SRCT character of the S1 state is conserved across all these solvents.