2‐ and 3‐Monohalogenated BODIPY Dyes and Their Functionalized Analogues: Synthesis and Spectroscopy

Abstract

Starting from appropriately halogenated acylpyrroles, a wide range of reactive 4,4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BODIPY) derivatives can be obtained. The fluorescent dyes display excellent reactivity in nucleophilic aromatic substitution, transition‐metal‐catalyzed cross‐coupling and copper‐catalyzed cycloaddition to azides (click chemistry). The spectral properties of the starting and final difluoroboron dipyrromethenes are discussed as a function of their structure.

Effect of the substitution position (2, 3 or 8) on the spectroscopic and photophysical properties of BODIPY dyes with a phenyl, styryl or phenylethynyl group

“…However, in contrast to what was observed for 8-Ph, but in accordance to what was found for 3-Ph, fwhmem, fwhmabs and  of 2-Ph increase roughly parallel with the dielectric constant  of the solvent. 3-Ph exhibits large  values, from 0.81 to 1.00, which are in good agreement with previously reported ones, 35,37 except for 3-Ph in toluene that shows a slightly larger  in this work. Regarding the rate constants of radiative (kf) and nonradiative (knr) S1 deactivation, 3-Ph shows an increase of kf with solvent refractive index n, from 1.6 × 10 8 s -1 in methanol to 2.2 × 10 8 s -1 in toluene, whereas knr ranges from negligible values in diethyl ether and 1,4-dioxane to 0.4 × 10 8 s -1 in methanol.…”

“…3-Ethyn exhibits large  values, from 0.77 (in cyclohexanone) to 1.00 in several solvents, which is in good agreement with previous reports. 35,37 Likewise, the fluorescence lifetime  decreases from 5.17 ns in methanol to 4.35 ns in chlorobenzene ( Figure S8). These  and  values involve an increase in kf in more polarizable solvents, ranging from (1.6-1.7) × 10 8 s -1 in acetonitrile and methanol to (2.2-2.3) × 10 8 s -1 in chlorobenzene and toluene, combined with low values for knr.…”

“…The synthesis of 2-Ph, 3-Ph, 2-Ethyn and 3-Ethyn was carried out by following our previously reported procedure, 37 whereas the synthesis of 8-Ph was performed as described by Kee et al 32 Also 8-Ethyn 26 and 3-Styryl 35 were synthesized prepared according to our protocols. Novel synthetic procedures for BODIPY derivatives 2-Styryl and 8-Styryl are described next.…”

“…3-Styryl displays a main, narrow S1S0 transition band (Figure 2A) similar to other 3-substituted boron dipyrromethenes. 35,37 The abs(max) values range from 549 to 561 nm, with a typical red shift from acetonitrile to chlorobenzene. The extended conjugation provided by the styryl functional group causes an extra bathochromic shift of around 20 nm with respect to 3-Ethyn, and ca.…”

“…In a preliminary study, our group described this effect for styryl and triazolyl substituents introduced at either the 3-or the 2-position. 35 n n n Chart 1. Representation of the "BODIPY core" and its IUPAC numbering system.…”