Synthesis and photophysical characteristics of 2,3,12,13-tetraalkylbacteriochlorins

Abstract

Bacteriochlorins absorb strongly in the near-infrared spectral region and hence are of great interest across the field of photochemistry. The established de novo self-condensation of a dihydrodipyrrinacetal has afforded stable bacteriochlorins bearing a variety of b-pyrrolic substituents, but the route was incompatible with the presence of two alkyl groups. The lacuna stemmed from the instability of the dialkyl-substituted dihydrodipyrrin-acetal. Here, two dihydrodipyrrin-carboxaldehydes, each bearing a tert-butoxycarbonyl group at the pyrrole a-position, were prepared and found to be stable to routine handling. Each ester-substituted dihydrodipyrrin-carboxaldehyde in acid underwent in situ ester cleavage and ensuing self-condensation to provide the corresponding 2,3,12,13-tetraalkylbacteriochlorin.The alkyl groups examined include methyl and methyl acetate. Such synthetic bacteriochlorins, while previously unknown, provide valuable models of the natural chromophores. The absorption and fluorescence characteristics of the tetraalkylbacteriochlorins are generally typical for this genre of macrocycle. The X-ray structure of the tetramethylbacteriochlorin reveals that the pyrrolinic (reduced) rings are modestly more twisted out-of-plane (torsional angle B111) than those of the nearly planar (torsional angle B11) parent bacteriochlorin that lacks pyrrolic tetraalkyl groups. The resonance Raman spectrum of the tetramethylbacteriochlorin is also far richer in the low-to mid-frequency region than that of the unsubstituted analogue, but like the unsubstituted counterpart, is far sparser in the highfrequency region than that of native bacteriochlorophyll. Access to tetraalkylbacteriochlorins constitutes one step on the path from the most simple, fully unsubstituted bacteriochlorin to the fully decorated, natural bacteriochlorophylls.

Synthesis and Spectral Properties of meso-Arylbacteriochlorins, Including Insights into Essential Motifs of their Hydrodipyrrin Precursors

“…A wide variety of dihydrodipyrrin-carboxaldehydes are now known and could be examined for reaction with an aryl Grignard reagent. Dihydrodipyrrin–carboxaldehyde 5 bears two β-methyl groups and a stabilizing α-ester unit [ 36 ]. Treatment of 5 with commercially available p -tolylmagnesium bromide gave the target dihydrodipyrrin–carbinol 6a in 56% yield ( Scheme 4 ).…”

“…The acetal unit has been the dominant group installed at the dihydrodipyrrin 1-position, and also has been the object of the most extensive refinement, yet other groups also have been explored [ 33 , 36 ]. Here, substitution of the 1-methyl group with both an aryl group and a hydroxy or acetoxy substituent gave rise to the corresponding bacteriochlorin, which is attributed to the stabilization imparted by the aryl group, with p -anisyl superior to p -tolyl for obvious electronic reasons ( Scheme 9 ).…”

“…The bacteriochlorins in Figure 4 enable incisive comparisons as follows. Bacteriochlorins B1 [ 36 ], B2 [ 31 , 44 ], iso-B2 [ 19 ], B3 [ 19 ], and B6 [ 36 ] contain no meso -aryl groups and serve as benchmarks to gauge the effects of meso -aryl incorporation. Bacteriochlorins B2 and iso-B2 are positional isomers (due to swapping the positions of the β-ethyl and β-carbethoxy groups).…”

“…Two routes rely on the self-condensation of a dihydrodipyrrin–acetal, either in an “Eastern-Western” (E-W) [ 18 ] or “Northern-Southern” (N-S) fashion, defined by the respective 3- versus 2-position of the gem-dimethyl group in the pyrroline ring of the dihydrodipyrrin–acetal (compare III and IV , Scheme 1 ) [ 19 ]. The routes along with creative extensions by others [ 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 ] have enabled preparation of >100 bacteriochlorins with specific substituent patterns for diverse applications [ 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 ].…”

Synthesis of Novel BTPhen-Functionalized Silica-Coated Magnetic Nanoparticles for Separating Trivalent Actinides and Lanthanides

“…[7][8][9][10] Separation of trivalent actinides from trivalent lanthanides is a challenging goal as the physicochemical properties of the two groups of elements are very similar. 11 This renders their chemical separation a challenging task, particularly given the high radioactivity of the waste necessitating the need for remote handling. Fortunately, previous studies have shown that separation of the minor actinides from lanthanides can be achieved by the SANEX solvent extraction process (Selective ActiNide EXtraction) using soft N-donor ligands containing the 1,2,4-triazine moiety (Figure 1).…”