Predicting solvatochromic shifts and colours of a solvated organic dye: The example of nile red

Abstract

The solvatochromic shift, as well as the change in colour of the simple organic dye nile red is studied in two polar and two non-polar solvents in the context of large-scale time-dependent density-functional theory (TDDFT) calculations treating large parts of the solvent environment from first principles. We show that an explicit solvent representation is vital to resolve absorption peak shifts between nile red in n-hexane and toluene, as well as acetone and ethanol. The origin of the failure of implicit solvent models for these solvents is identified as being due to the strong solute-solvent interactions in form of π-stacking and hydrogen bonding in the case of toluene and

Combining the ensemble and Franck-Condon approaches for calculating spectral shapes of molecules in solution

“…Having made the choice of ignoring all dynamic effects and the quantum nature of the nuclei in the computation of the absorption spectra, one has to consider how to represent the solvent environment of the chromophore. The two basic choices that can be made are between explicit solvent representations [8][9][10][11][27][28][29][30][31] and polarizable continuum models (PCMs) [1][2][3][4].…”

“…1 to yield an approximate absorption spectrum including average polarization effects by the solvent environment. However, in systems with significant solute-solvent interactions, pure PCM treatments can fail in correctly recovering absorption properties and solvatochromic shifts [10][11][12][13].…”

“…Being able to reproduce both the energy and the shape of the spectrum would be a rigorous test of a theoretical method, since it would require both accurate solutesolvent geometries, as well as accurate excited state methods for modeling the energy gap and intensity of transitions between electronic/vibrational states. Recent work [8][9][10][11][12][13][14][15][16] has shown that the explicit quantum mechanical (QM) treatment of significant parts of the solvent environment is essential in obtaining accurate and wellconverged excitation energies in a variety of systems, ranging from small dyes in solution to pigment-protein complexes. Because sampling of the inhomogeneous solvent environment is required, and because it is likely necessary to include the solvent explicitly in the quantum mechanical (QM) electronic structure calculation to obtain proper solute-solvent polarization and chargetransfer, the excited state method must be computationally efficient enough to perform many hundreds of calculations on a large QM region (with hundreds of atoms).…”

“…There are two dominant approaches for going beyond the computation of a single electronic excitation energy to compute a full absorption spectrum. The first way is through an ensemble approach, in which a Boltzmann sampling of nuclear configurations is obtained, often via a molecular dynamics (MD) ground state trajectory, and then excited state calculations are performed for each configuration [9,11,[26][27][28][29][30][31]. Many configurations, often termed 'snapshots' when obtained from an MD trajectory, are necessary for converging an absorption spectrum, so efficient excited state methods such as TDDFT are often used with this technique.…”

Evaluation of Nile Red‐Loaded Mesoporous Silica Nanoparticles for Developing Water‐Soaked Fingerprints on Thermal Paper

“…The intensity of the emission spectra of them is negligible compared to that in the presence of nile red. The emission blue shift accompanied by the fluorescence enhancement (~2.5 times) could be attributed to the interactions between the fatty residues of the fingerprints and nile red released from MSN@NR (38,39), in which these phenomena are very similar to the commonly observed solvent effect (40). The latent fingerprints emerged with yellow fluorescence under a 490 nm light irradiation because of the emission enhancement of MSN@NR upon contact with the fatty components of fingerprints, while the background (i.e., the regions without fatty components) remained lower fluorescence intensity, as shown in the red line (Fig.…”