TD-DFT Evaluation of Electronic Spectra of Coumarin and Anthraquinone Dyes: Effects of Functionals, Basis Sets, and Solvation Conditions

The electronic absorption spectra of 20 organic dyes
(7 coumarins,
10 anthraquinones, and 3 other similar molecules) were investigated
using TD-DFT with BLYP, B3LYP, and B3PW91 functionals and four basis
sets: 6-31++G(d,p), 6-311++G(2df,p), aug-cc-pVDZ, and aug-cc-pVTZ.
Gas-phase, implicit, and hybrid solvation models were tested. The
hybrid model, guided by electrostatic potential maps, yielded the
lowest mean absolute errors with respect to experimental absorption
maxima, underscoring the role of specific electrostatic solute–solvent
interactions. Overall, the solvent effects were most pronounced with
B3LYP and B3PW91. Replacing the LYP correlation functional with PW91
led to shifts of up to 6 nm, while modifying the exchange term from
B to B3 caused deviations of at least 33 nm. Basis set performance
was consistent across molecules, showing approximately linear trends.
Within this protocol, electrostatic-potential-guided microsolvation
provides an efficient way to capture key solute–solvent interactions
without resorting to more demanding QM/MM approaches.