Direct and Regioselective Amination of β‐Unsubstituted 5,15‐Diazaporphyrins with Amines: A Convenient Route to Near‐Infrared‐Responsive Diazaporphyrin Sensitizers

Abstract

We have established ac onvenient method for the base-promoted direct amination of b-unsubstituted 5,15-diazaporphyrins (DAPs) with secondary and primary amines to produce 3,7,13,17-tetraamino-and 3-amino-DAPs,r espectively,r egioselectively.T he amino groups attached at the periphery cause significant red shifts of the absorption bands as aresult of their perturbation of the HOMO and/or LUMO in the DAP p-system. The palladium complex of a3 ,7,13,17tetrakis(diphenylamino)-DAP generated singlet oxygen in high yield under irradiation with near-infrared light.Recently,considerableattentionhasbeenpaidtoporphyrin-Scheme 1. Synthesis of amino-DAPs. a) Nitration (to 2M-NO 2 )o r bromination (to 2M-Br); b) reduction (from 2M-NO 2 to P1)orN ÀC cross-coupling (from 2M-Br to P2); 3-NiDAP = 10,20-dimesityl-5,15diaza(nickel)porphyrin-3-yl. c) Base-promoted direct substitutionw ith amines (this study).Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.

Effects of the Peripheral Substituents, Central Metal, and Solvent on the Photochemical and Photophysical Properties of 5,15‐Diazaporphyrins

“…The redox potentials of MDAP‐COOEt in CH 2 Cl 2 were measured by cyclic voltammetry with Bu 4 NPF 6 as the electrolyte (Table and Figure S2 in SI). The first oxidation and reduction potentials ( E ox and E red ) of MDAP‐COOEt were slightly shifted to the positive side compared with the corresponding metal complexes P2 ( E ox =+0.01 to +0.16 V, E red =−1.57 to −1.49 V), reflecting the electron‐withdrawing effect of the ester groups . The energy gaps (Δ E = E ox − E red ) observed for MDAP‐COOEt (1.68–1.76 eV) were close to the optical HOMO–LUMO gaps determined from the absorption spectra (Δ E =ca.…”

“…MDAP‐COOEt showed two absorption bands, one of which ( λ max =711–715 nm) was likely to be the charge‐transfer band. The spectral shape of MDAP‐COOEt was similar to that of P2 , and there was almost no difference between the Cu II and Pd II complexes. The absorption spectra of MDAP‐COOH were somewhat broadened compared with those of MDAP‐COOEt, which may be because of a difference in the solvated structures of these dyes.…”

“…First, we synthesized MDAP‐COOEt according to a previously reported procedure . Briefly, treatment of 1M with bis(4‐ethoxycarbonylphenyl)amine in the presence of sodium ethoxide and molecular sieves (4 Å) in N , N ‐dimethylformamide (DMF) at room temperature afforded MDAP‐COOEt in moderate yield.…”

“…The absorption spectra of MDAP‐COOH were somewhat broadened compared with those of MDAP‐COOEt, which may be because of a difference in the solvated structures of these dyes. The slightly blue‐shifted λ max values of MDAP‐COOH in DMF may reflect the difference in electronic effects of the para ‐substituents on the excitation energies …”

“…In 2005, Shinmori, Osuka, and co‐workers reported the photosensitizing properties of 2,3,7,8,12,13,17,18‐octaalkyl‐DAPs P1 (Figure ), which were proven to be effective photosensitizers with 1 O 2 ‐generation quantum yields ( Φ Δ ) of 0.84–0.92 in toluene . During our ongoing study on β‐functionalized DAPs, we recently reported that DAPs bearing diphenylamino ( P2 ), phenoxy, or diethoxyphosphoryl group efficiently generated 1 O 2 under irradiation of visible or NIR light ( Φ Δ =0.92–0.99 in toluene). Independently, Shinokubo and co‐workers reported the in vitro and in vivo activity of the free bases of β‐unsubstituted DAP 1H 2 , 5,15‐diazachlorin P3 , and 5,15‐diazabacteriochlorin P4 (Figure ) in one‐ and two‐photon PDT .…”