Accessing the near-infrared spectral region with stable, synthetic, wavelength-tunable bacteriochlorins

Abstract

The near-infrared (NIR) spectral region has been comparatively under-utilized for diverse materials and medical applications owing to the lack of chromophores that afford stability, solubility, synthetic malleability, and tunable photophysical features. Bacteriochlorins are attractive candidates in this regard; however, preparation via modification of naturally occurring bacteriochlorophylls or reduction of porphyrins or chlorins has proved cumbersome. To overcome such limitations, a dibromobacteriochlorin (BC-Br 3 Br 13 ) was prepared de novo by the acid-catalyzed condensation of an 8-bromodihydrodipyrrin-acetal. BC-Br 3 Br 13 bears (1) a geminal dimethyl group in each reduced ring to block adventitious dehydrogenation, and (2) bromo groups at the 3-and 13-positions for further chemical modifications. BC-Br 3 Br 13 was subjected to four types of Pd-mediated coupling reaction (Suzuki, Stille, Sonogashira, dehalogenation) to give bacteriochlorins bearing substituents at the 3-and 13-positions (phenyl, vinyl, acetyl, phenylethynyl), and a benchmark bacteriochlorin lacking such substituents. The 3,13divinylbacteriochlorin was transformed to the 3,13-diformylbacteriochlorin. Depending on the substituents at the 3-and 13-positions, the position of the long-wavelength absorption maximum (Q y (0,0) band) lies between 713 and 771 nm, the fluorescence emission maximum lies between 717 and 777 nm, and the fluorescence quantum yield ranges from 0.15 to 0.070. The ability to introduce a wide variety of functional groups via Pd-mediated coupling reactions and the tunable absorption and emission spectral properties suggest that synthetic bacteriochlorins are viable candidates for a wide variety of photochemical applications.

[8π+2π] Cycloaddition of meso‐Tetra‐ and 5,15‐Diarylporphyrins: Synthesis and Photophysical Characterization of Stable Chlorins and Bacteriochlorins

“…[20] This stems from both the increased oscillator strength (extinction coefficient) of the long wavelength absorption [15] and the fact that most of the fluorescence intensity is concentrated in one long wavelength band. [21] In agreement with this, the absorption spectra of all four bacteriochlorins synthesized showed an intense absorption around 725 nm and a single fluorescence, with a small Stokes shift (3-6 nm). Typical spectra for bacteriochlorin 4d are shown in Figure 3 and all spectral and photophysical data are summarized in …”

Stable Synthetic Cationic Bacteriochlorins as Selective Antimicrobial Photosensitizers

“…2. The wavelength tunability of synthetic bacteriochlorins via functionalization of the 3-and 13-positions has been reported previously (50). The Q y absorption maxima of bacteriochlorins 1 to 4 in methanol are in the range 718 to 742 ( Table 1).…”

Deep-Red Emissive BODIPY–Chlorin Arrays Excitable with Green and Red Wavelengths

“…Additionally, wavelengths of absorption and emission maxima for hydroporphyrins can be precisely tuned by substitution on the periphery of the macrocycles. 2–5 Both the latter properties should greatly facilitate applications of hydroporphyrins as fluorophores for multicolor imaging. Recently, our collaborative efforts have demonstrated that unique properties of hydroporphyrins are highly beneficial for construction of fluorescent probes for anti-cancer fluorescence-guided surgery.…”