Microwave-assisted photooxidation of sulfoxides.

We demonstrated microwave-assisted photooxidation of sulfoxides to the corresponding sulfones using ethynylbenzene as a photosensitizer. Efficiency of the photooxidation was higher under microwave irradiation than under conventional thermal heating conditions. Under the conditions, ethynylbenzene promoted the oxidation more efficiently than conventional photosensitizers benzophenone, anthracene, and rose bengal. Ethynylbenzene, whose T1 state is extremely resistant to intersystem crossing to the ground state, was suitable to this reaction because spectroscopic and related reported studies suggested that this non-thermal effect was caused by elongating lifetime of the T1 state by microwave. This is the first study in which ethynylbenzene is used as a photosensitizer in a microwave-assisted photoreaction.

Near-Infrared-III-Absorbing and -Emitting Dyes: Energy-Gap Engineering of Expanded Porphyrinoids via Metallation.

The synthesis of organometallic complexes of modified 26π-conjugated hexaphyrins with absorption and emission capabilities in the third near-infrared region (NIR-III) is described. Symmetry alteration of the frontier molecular orbitals (MOs) of bis-PdII and bis-PtII complexes of hexaphyrin via N-confusion modification led to substantial metal dπ -pπ interactions. This MO mixing, in turn, resulted in a significantly narrower HOMO-LUMO energy gap. A remarkable long-wavelength shift of the lowest S0 →S1 absorption beyond 1700 nm was achieved with the bis-PtII complex, t-Pt2 -3. The emergence of photoacoustic (PA) signals maximized at 1700 nm makes t-Pt2 -3 potentially useful as a NIR-III PA contrast agent. The rigid bis-PdII complexes, t-Pd2 -3 and c-Pd2 -3, are rare examples of NIR emitters beyond 1500 nm. The current study provides new insight into the design of stable, expanded porphyrinic dyes possessing NIR-III-emissive and photoacoustic-response capabilities.

Synthesis of a Black Dye with Absorption Capabilities Across the Visible-to-Near-Infrared Region: A MO-Mixing Approach via Heterometal Coordination of Expanded Porphyrinoid.

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 light-harvesting black dyes for PT and PA applications.

Ring-Opened Hemiporphyrazines: Helical Molecules Exhibiting Circularly Polarized Luminescence.

We designed and synthesized a new type of small helical molecule exhibiting intense circularly polarized luminescence (CPL) (12H ) by modifying a 20π-electron hemiporphyrazine with a large transition magnetic dipole moment. The hemiporphyrazine ring was opened and one additional pyridine unit was introduced, resulting in an overlap of two pyridine rings. X-ray structure analysis confirmed that 12H and its zinc complex (1Zn ) adopt a helical geometry. A racemic mixture of 1Zn was resolved into two enantiomers ((P)- and (M)-1Zn ), which exhibited CPL with a high luminescence dissymmetry factor (glum ) value of ±2.1×10-2 . The origin of the large glum value was rationalized by means of DFT calculations. Helical structures could be formed in a diastereoselective manner by covalently attaching chiral units to the skeleton (1'2H and 1'Zn ). 1Zn was found to possess chiral recognition ability for amines.