Rationalizing the photophysical properties of BODIPY laser dyes via aromaticity and electron-donor-based structural perturbations

Abstract

Absorption Fluorescence DFT a b s t r a c tThe absorption and fluorescence properties of six boron dipyrromethene (BODIPY) laser dyes with simple non-aromatic substituents are rationalized by relating them to observable structural perturbations within the molecules of the dyes. An empirical relationship involving the structure and the optical properties is derived using a combination of single-crystal X-ray diffraction data, quantum chemical calculations and electronic constants: i.e. the tendency of the pyrrole bond lengths towards aromaticity and the UVevis absorption and fluorescence wavelengths correlate with the electron-donor properties of the substituents. The effect of molecular conformation on the solid-state optical properties of the dyes is also discussed. The findings in this study also demonstrate the usefulness and limitations of using crystal structure data to develop structure-property relationships in this class of optical materials, contributing to the growing effort to design optoelectronic materials with tunable properties via molecular engineering.

Synthesis, Properties, and Functionalization of Nonsymmetric 8‐MethylthioBODIPYs

“…Thus, the alkylation increases the HOMO energy and hence decreases the energy gap (Figure ), in concordance with the bathochromic shift registered for 27 vs. 25 or PM567 vs. PM546 (Table ). An increase in aromaticity between the pyrrole rings has also been pointed out to account for such spectral shifts upon substitution with electron‐donating groups at these last β‐positions …”

“…In fact, the short Stokes shift (<600 cm –1 ), suggest very small geometrical rearrangement in the excited state, and hence low internal conversion deactivation. Just slight deviations from planarity (up to 5° in the indacene core) are predicted upon substitution at positions 2 and 6, owing to the steric hindrance generated by the adjacent substituents, which leads to a slight butterfly‐like distortion in compounds 27 , 28 , and PM567 (Figure S2 in the Supporting Information).…”

“…An increase in aromaticity between the pyrrole rings has also been pointed out to account for such spectral shifts upon substitution with electron-donating groups at these last -positions. [16] Another significant issue is the asymmetry/symmetry of the alkylation pattern. Thus, compound 27 (with just one pyrrole unit fully alkylated) shows the lowest molar absorption (28000 M -1 cm -1 in Table 5).…”

“…Main resonance structures resulting from the electronic coupling of the 8-methylthio group with the BODIPY core and absorption spectra of dye 2 and its nonsymmetric(15)(16)(17)(18)(19) and symmetric (35-36) alkylated derivatives. For purposes of clarity, the absorption band has been deconvoluted into two lorentzians in the cases of selected representative compounds(15, 35, and 16).…”

Dibromo-BODIPY as an Organic Photocatalyst for Radical–Ionic Sequences

“…Many works using dyes like riboflavin, 2 eosin Y, 3 eosin B, 4 rose bengal, 5 and methylene blue, 6 among others, 7 as organic photocatalysts (OPCs) have been performed, demonstrating the importance of this area. In fact, fluorescent dyes have been widely studied in recent years due to their use as chemical sensors, 8 laser dyes, 9 drug delivery agents, 10 biomolecular labels, 11 therapeutics agents, 12 and sensitizers for singlet oxygen generation, 13 and in photovoltaic cells. 14 Among this diversity, those based on 4-bora-3a,4a-diaza-sindacene (BODIPY) exhibit a great potential due to its easy synthesis and derivatization, alongside the tenability of its photophysical proprieties.…”