Theoretical Investigation of the Circularly Polarized Luminescence of a Chiral Boron Dipyrromethene (BODIPY) Dye.

Qin Yang,Marco Fusè,Julien Bloino

doi:10.3389/fchem.2020.00801

Abstract

Over the last decade, molecules capable of emitting circularly polarized light have attracted growing attention for potential technological and biological applications. The efficiency of such devices depend on multiple parameters, in particular the magnitude and wavelength of the peak of emitted light, and also on the dissymmetry factor for chiral applications. In light of these considerations, molecular systems with tunable optical properties, preferably in the visible spectral region, are particularly appealing. This is the case of boron dipyrromethene (BODIPY) dyes, which exhibit large molecular absorption coefficients, have high fluorescence yields, are very stable, both thermally and photochemically, and can be easily functionalized. The latter property has been extensively exploited in the literature to produce chromophores with a wide range of optical properties. Nevertheless, only a few chiral BODIPYs have been synthetized and investigated so far. Using a recently reported axially chiral BODIPY derivative where an axially chiral BINOL unit has been attached to the chromophore unit, we present a comprehensive computational protocol to predict and interpret the one-photon absorption and emission spectra, together with their chiroptical counterparts. From the physico-chemical properties of this molecule, it will be possible to understand the origin of the circularly polarized luminescence better, thus helping to fine-tune the properties of interest. The sensitivity of such processes require accurate results, which can be achieved through a proper account of the vibrational structure in optical spectra. Methodologies to compute vibrationally-resolved electronic spectra can now be applied on relatively large chromophores, such as BODIPYs, but require more extensive computational protocols. For this reason, particular attention is paid in the description of the different steps of the protocol, and the potential pitfalls. Finally, we show how, by means of appropriate tools and approaches, data from intermediate steps of the simulation of the final spectra can be used to obtain further insights into the properties of the molecular system under investigation and the origin of the visible bands.

Highlights

Polarized luminescence (CPL) processes have gained interest over the years for their potential use in technological applications, such as data storage or optical displays, as well as for the design of novel biological probes (Riehl and Richardson, 1986; Furumi, 2010; Carr et al, 2012; Kumar et al, 2015; Sánchez-Carnerero et al, 2015; Zinna and Di Bari, 2015; Longhi et al, 2016; Jimènez et al, 2017; Li et al, 2018)
With the aim of characterizing the nature of this process and understand the chiroptical properties of this chiral O-boron dipyrromethene (BODIPY), we present an extensive computational protocol, starting from the definition of the electronic structure calculation method based on their overall performance up to the simulation of the vibrationally-resolved electronic spectra
The results for the BODIPY dye will be presented, following the workflow described in the previous section, which can be summarized as: (i) exploration of the conformational space in order to define the low-lying conformational ensemble; (ii) choice of the best level of theory to reproduce the spectroscopic property of interest; (iii) inclusion of vibrational effects to the pure electronic transitions

Summary

Introduction

Polarized luminescence (CPL) processes have gained interest over the years for their potential use in technological applications, such as data storage or optical displays, as well as for the design of novel biological probes (Riehl and Richardson, 1986; Furumi, 2010; Carr et al, 2012; Kumar et al, 2015; Sánchez-Carnerero et al, 2015; Zinna and Di Bari, 2015; Longhi et al, 2016; Jimènez et al, 2017; Li et al, 2018). A relatively straightforward strategy is to start with a promising core structure, whose physico-chemical properties can be tuned through chemical substitutions or additions Among such tunable systems, Boron dipyrrin (4-bora3a,4a-diaza-s-indacene, BODIPY) derivatives represent an important family of organic molecules that have shown excellent performance in photonic applications, such as 3D optical displays, storage, spintronics, or biological probes (DuránSampedro et al, 2013; Lifschitz et al, 2013; Wang et al, 2013; Liu et al, 2014; Zhao et al, 2015; Kaur and Singh, 2019; Turksoy et al, 2019), thanks to their absorption and emission properties in the visible spectra region, which can be manipulated (Loudet and Burgess, 2007; Ulrich et al, 2008; Wang et al, 2013; Liu et al, 2014; Zhao et al, 2015). Through a description and illustration of their capabilities, it will be possible to design a comprehensive, and evolutive, protocol for the study of chiroptical spectra of medium-to-large molecular systems beyond the standard, purely electronic methods

Methods

Results

Conclusion