Synthetic Approach to Readily Accessible Benzofuran-Fused Borondipyrromethenes as Red-Emitting Laser Dyes

Abstract

We took advantage of the chemoselective meso-functionalization of 2,3,5,6-tetrabromo-8-methylthioBODIPY 6 to prepare a series of 2,3,5,6-tetrabromo-8-arylBODIPY derivatives suitable for SNAr substitution reactions with phenols exclusively at positions 3 and 5. Pd(0)-catalyzed intramolecular arylation reaction ensued on the remaining brominated positions 2 and 6 to give a new family of benzofuran-fused BODIPY dyes. This method utilizes readily available starting materials and allows for the preparation of the title compounds with excellent functional group tolerance. Moreover, it was demonstrated that the methodology described herein is amenable for the incorporation of biomolecules. The photophysical and lasing properties of the benzofuran-fused BODIPY dyes were thoroughly analyzed with the aid of electrochemical measurements and quantum mechanical simulations. These dyes show bright and intriguing emission (both fluorescence and laser) toward the red edge of the visible spectrum with remarkable tolerance under strong and continuous irradiation.

A Palette of Efficient and Stable Far-Red and NIR Dye Lasers

“…The presence of electron donor moieties (RED7, RED9, and RED11) and mainly the further fusion of more aromatic groups (RED8) induce a more pronounced shift to the red edge, from 575 to 610 nm (Figures 3 and 4). Such spanning of the aromaticity is reflected in a remarkable enhancement of the absorption probability (molar absorption coefficient), being twice that recorded for simpler BODIPYs, and reaching values approaching 200,000 M −1 •cm −1 (Figures 3 and 4) [47]. The corresponding fluorescence bands are located in a spectral window ranging from 595 to 625 nm.…”

“…The laser dyes designed to cover the far-red region of the visible spectrum are based on a BODIPY core bearing fused benzofuran rings with different substitution patterns (fluorine, alkyls, linear alcoxys, or additional fused rings) [47]. The corresponding molecular structures and main photophysical and laser data are summarized in Figure 3.…”

“…The exceptions to this behavior are due to an increase in the non-radiative deactivation processes induced by the substitution pattern. For instance, in RED5, the combination of electron donor benzofuran with electron formaldehyde at the para-8-aryl favors charge separation and reduces the emission capability [47]. In RED8 and RED11, the geometrical tensions induced by the additional fused phenyls could promote the bending of the chromophore, thereby distorting the planarity and increasing the internal conversion [47].…”

“…To circumvent such restriction, complex and bulky experimental set-ups are required. Therefore, to offset this deficiency, we developed red and NIR dye lasers with improved photonic performance, particularly focused on enhancing the photostability, i.e., benzofuran-fused BODIPYs (Section 2) as laser dyes emitting in the far-red region of the visible spectral region [47] and polyarylated aza-BODIPYs (Section 3) for the NIR spectral region (Figure 2) [48]. Hereafter, we overview the photophysical and laser properties of these novel BODIPYs designed in our laboratories and compare their photonic performance with commercially available laser dyes working in the same spectral region.…”

Exploring N-BODIPYs as Privileged Scaffolds to Build Off/On Fluorescent Sensors by PET

“…Thus, the BODIPY chromophores usually emit a relatively sharp fluorescent peak with high fluorescence quantum yield and a high molar absorption coefficient [4,5]. They also have good solubility, chemical robustness, thermal and photochemical stability, and are one of the few structures that can fluoresce over the entire visible and in the near-IR electromagnetic spectrum, if they are modified accordingly [5][6][7].…”