A combined Monte Carlo/DFT approach to simulate UV‐vis spectra of molecules and aggregates: Merocyanine dyes as a case study

Abstract

The combination of a Monte Carlo (MC) sampling of the configurational space with time dependent‐density functional theory (TD‐DFT) to estimate vertical excitations energies has been applied to compute the absorption spectra of a family of merocyanine dyes in both their monomeric and dimeric forms. These results have been compared to those obtained using a static DFT/TD‐DFT approach as well as to the available experimental spectra. Though suffering of the limitations related to the use of DFT and TD‐DFT for this type of systems, our data clearly show that the classical MC sampling provides a suitable alternative to classical molecular dynamics to explore the structural flexibility of these donor‐acceptor (D‐π‐A) chromophores enabling a realistic description of the potential energy surface of both their monomers and aggregates (here dimers) and thus of their spectra. Overall, the combination of MC sampling with quantum mechanics (TD‐DFT) calculations, carried out in implicit dioxane solvent on random snapshots, provides a workable compromise to solve the combined challenge of accuracy and time‐consuming problem not only for merocyanines momers, but also for their dimers, up to now less investigated. Indeed, the simulated absorption spectra fairly agree with the experimental ones, suggesting the general reliability of the method.

Spiropyran/Merocyanine Amphiphile in Various Solvents: A Joint Experimental–Theoretical Approach to Photophysical Properties and Self-Assembly

“…All the measurements are conducted at pH 7. In the last paragraph we would like to mention that calculated and measured photophysical spectra (mainly positions of the absorption bands and solvatochromism) are consistent with the reported in the literature [26,27,30,32,45,53,67,69,73,[77][78][79]104,111,112] findings for the positive photochromic spiropyran systems, as well as for still rare data concerning photoisomerization of SP/MC-containing surfactants, exhibiting negative photochromism.…”

“…Upon irradiation with UV light or after dissolution in water, the TMAB-C3-SP form is transformed into the opened TMAB-C3-MC form, accompanied by a solution color change. The visualization of the excitations in MC isomer (Figure 9b) illustrates delocalized conjugated nature of the molecule, which is supported by the majority of theoretical studies [67,77,79,97,110]. The excitations at 504-516nm are attributed to the π − π * transition of the opened form [43].…”

“…The vertical transition energies to the first 100 excited states are calculated for each isomer having optimized geometries in a particular solvent using time-dependent DFT with the B3LYP [69], PBE [77] functionals and the DGDZVP and 6-311G * basis set, correspondingly. The DGDZVP basis set is shown to predict the energies close with respect to the experiment transition energies, e.g.…”

Spiropyran/Merocyanine Amphiphile in Various Solvents: A Joint Experimental–Theoretical Approach to Photophysical Properties and Self-Assembly

“…Upon irradiation with UV light or after dissolution in water, the TMAB-C3-SP form is transformed into the opened TMAB-C3-MC form, accompanied by a solution color change. The visualization of the excitations in the MC isomer ( Figure 8 b) illustrates more delocalized conjugated nature of the molecule, which is supported by the majority of theoretical studies [ 56 , 71 , 75 , 87 ]. The excitations at 504–516 nm are attributed to the transition of the opened form [ 35 ].…”

Solvophobically‐Driven Merocyanine Dye Assembly: Predominant Dipole‐Dipole Interactions Over Hydrogen‐Bonding

“…Indeed, range-separated hybrid DFT methods are reported to provide spectral information in agreement to experiments for merocyanine dyes, validating the choice of the method and reliability of the relative energies in the present case. [19] The computational parallelly stacked model displayed OÀ H•••O=C hydrogen bonds in the range of 1.78-1.88 Å with extended π-π stacking distance of 3.48-3.56 Å along the perpendicular axis. [20] The OÀ HÀ O hydrogen-bonding angle was predicted at θ = 170°, in congruence with the crystal structure (θ = 163.12°).…”