NBD and its derivatives, due to high sensitivity to the polarity of the environment, are routinely used as fluorescent dyes. In aprotic solvents like DMSO, NBD acts as a hydrogen bond donor via the chromophore's NH 2 group, potentially forming two hydrogen bonds with the oxygen atom in the DMSO solvent. For the first excited state, which is also the bright state of interest here, there is a partial intramolecular charge-transfer character driving the observed fluorescence. The FWHM of experimental 123 absorption and emission lineshapes (after the scaling correction discussed in Eqs. 6-7) are 0.341 and 0.400 eV, respectively, suggesting potentially an increase in the flexibility of the molecule in the excited state or an increase in the strength of the chromophore-solvent interactions compared to the ground state. The lineshape Stokes shift is moderate at 0.334 eV.