Engineering topics
Publications and source records attributed to Krayer, Michael.
Bacteriochlorins with phenaleno or benzo annulation absorb at 913 or 1033 nm and exhibit excited-state lifetimes of 150 or 7 ps, suggesting applications in photoacoustic imaging.
Compound of Formula I: are described, along with compositions containing the same and methods of use thereof. ##STR00001##
Abstract Understanding the effects of substituents on spectral properties is essential for the rational design of tailored bacteriochlorins for light‐harvesting and other applications. Toward this goal, three new bacteriochlorins containing previously unexplored conjugating substituents have been prepared and characterized. The conjugating substituents include two positively charged species, 2‐( N ‐ethyl 2‐quinolinium)vinyl‐ (B‐1) and 2‐( N ‐ethyl 4‐pyridinium)vinyl‐ (B‐2), and a neutral group, acroleinyl‐ (B‐3); the charged species resemble cyanine (or styryl) dye motifs whereas the neutral unit resembles a merocyanine dye motif. The three bacteriochlorins are examined by static and time‐resolved absorption and emission spectroscopy and density functional theoretical calculations. B‐1 and B‐2 have Q y absorption bathochromically shifted well into the NIR region (822 and 852 nm), farther than B‐3 (793 nm) and other 3,13‐disubstituted bacteriochlorins studied previously. B‐1 and B‐2 have broad Q y absorption and fluorescence features with large peak separation (Stokes shift), low fluorescence yields, and shortened S 1 ( Q y ) excited‐state lifetimes (~700 ps and ~100 ps). More typical spectra and S 1 lifetime (~2.3 ns) are found for B‐3. The combined photophysical and molecular‐orbital characteristics suggest the altered spectra and enhanced nonradiative S 1 decay of B‐1 and B‐2 derive from excited‐state configurations in which electron density is shifted between the macrocycle and the substituents.
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Synthetic bacteriochlorins enable systematic tailoring of substituents about the bacteriochlorin chromophore and thereby provide insights concerning the native bacteriochlorophylls of bacterial photosynthesis. Nine free-base bacteriochlorins (eight prepared previously and one prepared here) have been examined that bear diverse substituents at the 13- or 3,13-positions. The substituents include chalcone (3-phenylprop-2-en-1-onyl) derivatives with groups attached to the phenyl moiety, a “reverse chalcone” (3-phenyl-3-oxo-1-enyl), and extended chalcones (5-phenylpenta-2,4-dien-1-onyl, retinylidenonyl). The spectral and photophysical properties (τ s , Φ f , Φ ic , Φ isc , τ T , k f , k ic , k isc ) of the bacteriochlorins have been characterized. The bacteriochlorins absorb strongly in the 780–800 nm region and have fluorescence quantum yields (Φ f ) in the range 0.05–0.11 in toluene and dimethylsulfoxide. Light-induced electron promotions between orbitals with predominantly substituent or macrocycle character or both may give rise to some net macrocycle ↔ substituent charge-transfer character in the lowest and higher singlet excited states as indicated by density functional theory (DFT) and time-dependent DFT calculations. Such calculations indicated significant participation of molecular orbitals beyond those (HOMO -- 1 to LUMO + 1) in the Gouterman four-orbital model. Taken together, the studies provide insight into the fundamental properties of bacteriochlorins and illustrate designs for tuning the spectral and photophysical features of these near-infrared-absorbing tetrapyrrole chromophores.
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