Near-Infrared-Iii-Absorbing And -Emitting Dyes: Energy-Gap Engineering Of Expanded Porphyrinoids Via Metallation

The synthesis of organometallic complexes of modified 26 pi-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-Pd(II)and bis-Pt(II)complexes of hexaphyrin via N-confusion modification led to substantial metal d(pi)-p(pi)interactions. This MO mixing, in turn, resulted in a significantly narrower HOMO-LUMO energy gap. A remarkable long-wavelength shift of the lowest S-0 -> S(1)absorption beyond 1700 nm was achieved with the bis-Pt(II)complex,t-Pt-2-3. The emergence of photoacoustic (PA) signals maximized at 1700 nm makest-Pt-2-3potentially useful as a NIR-III PA contrast agent. The rigid bis-Pd(II)complexes,t-Pd-2-3andc-Pd-2-3, 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.