TD-DFT analysis of the excitation of H-dimers of cationic dyes in an aqueous solution using functionals without additional dispersion correction

This work is a development and extension of the previous one (DOI: 10.1039/d3cp00882g ). Here, H-dimers of acridine (acridine orange—AO and proflavine—PF), thiazine (methylene blue—MB and thionine—TH), and oxazine (brilliant cresyl blue—BCB and Nile blue—NB) dyes were modeled using hybrid functionals with a large proportion of exact Hartree–Fock exchange and long-range correction. It turned out that nine functionals (LC-ωHPBE, M06HF, M052X, M062X, M08HX, M11, MN15, SOGGA11X, and ωB97XD) reliably stabilize these molecular aggregates in both the ground and excited states. In addition, these functionals ensure that the conditions for transition moments (M(dimer) ≈ $\sqrt{2}$M(monomer) from strong coupling theory for H-aggregates) and absorption maxima (λ_max(dimer) < λ_max(monomer) from Kasha exciton theory) are met. The S₂ excited state stabilizes the H-dimers more strongly than the ground state, while the S₁ state stabilizes even more than S₂. This is due to the large overlap between the corresponding molecular orbitals (LUMO > HOMO−1 > HOMO). When calculating the vibronic absorption spectra, the best agreement with the experiment for AO₂, PF₂, and NB₂ showed the M08HX functional, and M11—for MB₂ and BCB₂. For dye monomers, these functionals gave the worst agreement, and MN15 demonstrated the closest similarity to the experiment. Vibronic absorption spectra for AO₂, MB₂, BCB₂, and NB₂ were calculated for the first time. The exciton splitting is calculated, which for MB₂ is in good agreement with the experimental value.