We
investigated the detailed photophysical properties of a series
of bis-metal (Zn and Cu) dioxohexaphyrin complexes as potential second
near-infrared (NIR-II)-light responsive dyes. A cisoid-configured 28π-electron-conjugated dioxohexaphyrin analogue
(
c
-3a) containing two peculiar
“confused pyrrole” moieties in the framework is identified
as a reduced isomer derivative of a transoid 26π-dioxohexaphyrin
(
t
-2a). The symmetry-altered
structure of
c
-3a affords
a heteroleptic inner environment within the NNNN/NNOO donor core, which imparts its highly flexible electronic
features and nonplanar geometry. The macrocycle
c
-3a can be transformed into the corresponding
26π-electron congener (
c
-2a) having a coplanar rectangular structure by unique solvent-mediated
redox reactivity. Furthermore, upon metal complexation, saddle-distorted
bis-metal complexes (
c-
M
2
-2a) were formed as the 26π-conjugated
structural isomer of the trans-dioxohexaphyrin species
(i.e.,
t
-M
2
-2a). These isoelectronic dioxohexaphyrins
demonstrate precise geometry-dependent photophysical properties. Broad
tailing NIR-II absorption, weak emissive character, and rapid-decay
of the S1 state are observed for
c
-Zn
2
-2a. In contrast, the coplanar
t
-M
2
-2a exhibits efficient
photoacoustic response upon laser excitation with NIR-II light (λ
> 1000 nm). To the best of our knowledge, this is the first example
of an expanded porphyrin-based photoacoustic contrast agent responsive
to NIR-II light.
An expanded metalloporphyrin-based "black dye" Au−Pd oxohexaphyrin (AuPd-1) with absorption capabilities across the visible-to-near-infrared (NIR) range was synthesized. This black dye, AuPd-1, possessed efficient light-harvesting and photostable capabilities, which were indicative of superior photothermal (PT) conversion abilities. Encapsulation of AuPd-1 with a micellar nanocapsule resulted in a compound that demonstrated intense photoacoustic (PA) properties in the NIR region in water. This finding indicated how metal (d)−ligand (π) molecular orbital interactions in metalloporphyrins could aid in the design of visible-to-NIR lightharvesting black dyes for PT and PA applications.
A hybrid thia‐norhexaphyrin comprising a directly linked N‐confused pyrrole and thiophene unit (1) revealed unique macrocycle transformations to afford multiply inner‐annulated aromatic macrocycles. Oxidation with 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone triggered a cleavage of the C−S bond of the thiophene unit, accompanied with skeletal rearrangement to afford unique π‐conjugated products: a thiopyrrolo‐pentaphyrin embedded with a pyrrolo[1,2]isothiazole (2), a sulfur‐free pentaphyrin incorporating an indolizine moiety (3), and a thiopyranyltriphyrinoid containing a 2H‐thiopyran unit (4). Furthermore, 2 underwent desulfurization reactions to afford a fused pentaphyrin containing a pyrrolizine moiety (5) under mild conditions. Using expanded porphyrin scaffolds, oxidative thiophene cleavage and desulfurization of the hitherto unknown N‐confused core‐modified macrocycles would be a practical approach for developing unique polypyrrolic aromatic macrocycles.
Ah ybrid thia-norhexaphyrin comprising ad irectly linked N-confused pyrrole and thiophene unit (1)r evealed unique macrocycle transformations to affordm ultiply innerannulated aromatic macrocycles.Oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone triggered acleavage of the C À S bond of the thiophene unit, accompanied with skeletal rearrangement to affordu nique p-conjugated products:athiopyrrolo-pentaphyrin embedded with apyrrolo[1,2]isothiazole (2), as ulfur-free pentaphyrin incorporating an indolizine moiety (3), and at hiopyranyltriphyrinoid containing a2 Hthiopyran unit (4). Furthermore, 2 underwent desulfurization reactions to affordafused pentaphyrin containing apyrrolizine moiety (5)u nder mild conditions.U sing expanded porphyrin scaffolds,o xidative thiophene cleavage and desulfurization of the hitherto unknown N-confused core-modified macrocycles would be ap ractical approachf or developing unique polypyrrolic aromatic macrocycles.Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.
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