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.
Arsenic ligands have attracted considerable attention in coordination chemistry. Arsenic(III) halides are the most important starting materials in the preparation of monodentate arsenic ligands. In this work, we optimized the synthetic methodologies of arsenic(III) halides (AsX 3 ; X = Br, I) and examined the difference of their physical properties such as solubility to organic solvent and reactivity to nucleophiles. In addition, a wide variety of monodentate arsenic ligands were prepared with the obtained AsX 3 . Finally, the obtained monodentate arsenic ligands were utilized for copper-free Sonogashira cross-coupling reaction in the reaction system with porphyrin. The results showed that monodentate arsenic ligands have higher catalytic activity compared with triphenylphosphine because of the difference of the electronic features of lone pairs between arsenic and phosphorus atoms.
Novel site-selective hetero-copper(II)/zinc(II) complexes of a cisoid-configured doubly N-confused dioxohexaphyrin analog (c-ZnCu-2 and c-CuZn-2) were synthesized and characterized. The resulting heterometal complexes exhibited a unique near-infrared (NIR) absorption feature, and the facile redox-active properties originated from the large 26[Formula: see text]-conjugated structure. The distinct difference between the site-dependent c-ZnCu-2 and c-CuZn-2appeared in the specific structural parameters of the d9 copper centers in the electron paramagnetic resonance spectra and the Lewis acidity of the zinc centers upon the base-titrations. These complexes have potential for the hetero-metal-containing [Formula: see text]-material applications that respond to the NIR light.
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