Simulation workflows to predict the circular dichroism and circularly polarized luminescence of chiral materials

Abstract

Chiral materials are attracting considerable interest in various fields in view of their unique properties and optical activity. Indeed, the peculiar features of chiral materials to absorb and emit circularly polarized light enable their use in an extensive range of applications. Motivated by the interest in boosting the development of chiral materials characterized by enhanced chiroptical properties such as circular dichroism (CD) and circular polarized luminescence (CPL), we herein illustrate in this tutorial how theoretical simulations can be used for the predictions and interpretations of chiroptical data and for the identification of chiral geometries. We are focusing on computational frameworks that can be used to investigate the theoretical aspects of chiral materials' photophysical and conformational characteristics. We will then illustrate ab initio methods based on density functional theory (DFT) and its time‐dependent extension (TD‐DFT) to simulate CD and CPL signals, and we will exemplify a variety of enhanced sampling techniques useful for an adequate sampling of the configurational space for chiral systems.

A Perspective on the Simulation of Electronic Circular Dichroism and Circularly Polarized Luminescence Spectra in Chiral Solid Materials

“…Therefore, strategies for conformational searches will be necessary, and spectra will be calculated for multiple configurations. These searches could be performed with classical molecular dynamics (MD) simulations or with other available protocols. ,, Then, the relevant structures would be optimized at the QM level in the ground state for ECD and possibly in the first excited state for CPL. In the excited state, one may find multiple minimum structures that could be accessible from these ground state conformers.…”

“…Most of the calculations of ECD and CPL in materials have been done using the exciton chirality method (ECM), which is based on the exciton coupling between coupled oscillators; see Figure . ,− This method can be used when a chiral molecule contains two or more “separate” chromophores undergoing electric-dipole-allowed transitions; in a molecular material, the coupled transitions can occur between separate molecular units. If the relative orientation of the chromophores and the orientation of the electric transition dipole for each chromophore are known, then the ECM provides a fairly simple way to determine the ECD spectrum of the system.…”

Chiral self-organization of the TPPS4 porphyrin assisted by molecular rotations

“…2 During the past few years, many efforts were devoted to clarifying how the chiral information is transferred via specific interactions and propagates through the supramolecular scaffold. [1][2][3][4][5][6][7][8][9] In this framework, chiral aggregates of porphyrins are of particular interest as model systems and widely studied owing to their potential manifold applications in organic electronics, [10][11][12] optoelectronics, 1,6 and non-linear optics, 11 as well as photoconductivity. 13 Aiming at creating advanced functional materials with unusual optical properties, the spatial arrangement of porphyrins can be modulated through non-covalent intermolecular interactions.…”

“…2 During the past few years, many efforts were devoted to clarifying how the chiral information is transferred via specific interactions and propagates through the supramolecular scaffold. 1–9…”

Calculating the Circular Dichroism of Chiral Halide Perovskites: A Tight-Binding Approach

“…Calculations for molecules typically focus on the rotatory strength based on the Rosenberg expression. − The latter requires transition matrix elements of electric and magnetic dipole operators and involves an averaging over molecular orientations, under the assumption that each orientation is equally probable. In a crystal, orientations are fixed to the lattice apart from vibrations; therefore, orientational averaging is not appropriate.…”