Absorption, emission and excitation spectra of dyes 7 and 8 have been recorded in various solvents with different polarity properties (Table , Fig. ). These spectra are characterized by an absorption band in the 500-650 nm spectral range as well as through pronounced vibronic progression (≈1520 cm -1 ); however, only a slight modification of spectral bandwidth and position of absorption maximum have been observed as a function of solvent polarity. Excitation and fluorescence spectra are very poorly solvent-dependent as well. Fluorescence quantum yields (Φfl ) reveal, a dramatically opposite behavior between dyes 7 (Φfl =0.76) and 8 (Φfl =0.09) in non-polar and slightly polar solvents (CCl4 and toluene). At the same time a decreasing trend in fluorescence quantum yield is observed for both compounds as the polarity of the environment is increased (Φfl =0.16 for dyes 7 and Φfl =0.03 for 8 in BZN). The virtually absent response of emission maximum (λem max ) to solvent polarity for both dyes 7 and 8 indicate that the emissive excited state may be described as quadrupolar in character. However, the fluorescence emission quenching (for dyes 7 and 8) as the polarity of the solvent is increased from dye 7 to 8, suggest that an additional excited state plays key role in deactivation pathway. Given that molar absorption coefficients are ≈ 140,000 in both cases, the optical brightness reaches almost 110,000 in toluene.