Quantum Mechanics/Fluctuating Charge Protocol to Compute Solvatochromic Shifts.

Matteo Ambrosetti,Chiara Cappelli,Tommaso Giovannini,Sulejman Skoko

doi:10.1021/acs.jctc.1c00763

Matteo Ambrosetti, Chiara Cappelli + Show 2 more

Open Access

https://doi.org/10.1021/acs.jctc.1c00763

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Abstract

Despite the potentialities of the quantum mechanics (QM)/fluctuating charge (FQ) approach to model the spectral properties of solvated systems, its extensive use has been hampered by the lack of reliable parametrizations of solvents other than water. In this paper, we substantially extend the applicability of QM/FQ to solvating environments of different polarities and hydrogen-bonding capabilities. The reliability and robustness of the approach are demonstrated by challenging the model to simulate solvatochromic shifts of four organic chromophores, which display large shifts when dissolved in apolar, aprotic or polar, protic solvents.

Highlights

The study of electronic and optical properties of chromophores is of particular interest for many different applications, ranging from photochemistry to technology.[1]
We analyze the transition involved in the spectral signal, and we compare the QM/FQ values with EE (QM/EE) and continuum solvation approaches (QM/PCM), so as to disentangle the role of explicit solute−solvent interactions and polarization effects
PNA belongs to the family of “push−pull” organic compounds, being characterized by an electron-donor amino group (NH2) and a para electronacceptor nitro group (NO2), which are connected by a πconjugated phenyl ring

Summary

Introduction

The study of electronic and optical properties of chromophores is of particular interest for many different applications, ranging from photochemistry to technology.[1] In most cases, such optical properties are tuned by dissolving the selected dye in different solvents, which can yield to substantial changes in the solute’s properties.[2] When dealing with electronic excitations, solvent effects mainly manifest in a shift of the solute’s absorption band,[3] which is usually referred to as solvatochromism, or a solvatochromic shift.[2,4−10] Depending on the nature of the transition, blue or red shifts are observed;[2] reliable computational approaches are needed to correctly reproduce both the “sign” of the solvatochromic shift and its magnitude as a function of the nature of the solvent.[9] To this end, different methods have been proposed, generally focusing the attention on the solute, which is responsible for the spectral signal and is accurately described at the quantum-mechanics (QM) level. The computational cost of QM/MM methods being much lower than those of most quantum embedding methods, the former are rapidly becoming the golden standard for many applications,[18,25,26] especially those refined approaches, which are able to correctly take into account solute−solvent mutual polarization effects (i.e., in the so-called polarizable QM/MM embedding methods).[3,18,26−29]

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