Fine-Tuning of Nonlinear Optical Contrasts of Hexaphyrin-Based Molecular Switches Using Inverse Design

• Published in: Frontiers in chemistry 2021-12, Vol.9, p.786036-786036
• Main Authors: Desmedt, Eline, Woller, Tatiana, Teunissen, Jos L, De Vleeschouwer, Freija, Alonso, Mercedes
• Format: Article
• Language: English
• Subjects: (time-dependent) density functional theory; best-first search algorithm; Chemistry; expanded porphyrins; inverse design; molecular switches; nonlinear optical properties
• ISSN: 2296-2646; 2296-2646
• DOI: 10.3389/fchem.2021.786036

In the search for new nonlinear optical (NLO) switching devices, expanded porphyrins have emerged as ideal candidates thanks to their tunable chemical and photophysical properties. Introducing -substituents to these macrocycles is a successful strategy to enhance the NLO contrasts. Despite its potential, the influence of -substitution on their structural and geometrical properties has been scarcely investigated. In this work, we pursue to grasp the underlying pivotal concepts for the fine-tuning of the NLO contrasts of hexaphyrin-based molecular switches, with a particular focus on the first hyperpolarizability related to the hyper-Rayleigh scattering ( ). Building further on these concepts, we also aim to develop a rational design protocol. Starting from the (un)substituted hexaphyrins with various -conjugation topologies and redox states, structure-property relationships are established linking aromaticity, photophysical properties and responses. Ultimately, inverse molecular design using the best-first search algorithm is applied on the most favorable switches with the aim to further explore the combinatorial chemical compound space of -substituted hexaphyrins in search of high-contrast NLO switches. Two definitions of the figure-of-merit of the switch performance were used as target objectives in the optimization problem. Several -substitution patterns and their underlying characteristics are identified, uncovering molecular symmetry and the electronic nature of the substituents as the key players for fine-tuning the values and NLO contrasts of hexaphyrin-based switches.