Doubly N‐Confused Calix[6]phyrin Bis‐Organopalladium Complexes: Photostable Triplet Sensitizers for Singlet Oxygen Generation

Triplet photosensitizers that generate singlet oxygen efficiently are attractive for applications such as photodynamic therapy (PDT). Extending the absorption band to a near‐infrared (NIR) region (700 nm≈) with reasonable photostability is one of the major demands in the rational design of such sensitizers. We herein prepared a series of mono‐ and bis‐palladium complexes ( 1‐Pd‐H₂ , 2‐Pd‐H₂ , 1‐Pd‐Pd , and 2‐Pd‐Pd ) based on modified calix[6]phyrins as photosensitizers for singlet oxygen generation. These palladium complexes showed intense absorption profiles in the visible‐to‐NIR region (500–750 nm) depending on the number of central metals. Upon photoirradiation in the presence of 1,5‐dihydroxynaphthalene (DHN) as a substrate for reactive oxygen species, the bis‐palladium complexes generated singlet oxygen with high efficiency and excellent photostability. Singlet oxygen generation was confirmed from the characteristic spectral feature of the spin trapped complex in the EPR spectrum and the intact ¹O₂ emission at 1270 nm.     

α-Acrylaldehyde 3-Pyrrolyl BODIPY as a Specific Optical Sensor for Cysteine and Homocysteine

A new fluorophore, α-acrylaldehyde 3-pyrrolyl BODIPY was synthesized by treating 3-pyrrolyl BODIPY with a mixture of 3-(dimethylamino) acrolein and POCl₃ under Vilsmeier–Haack reaction conditions. The X-ray structure revealed that the fluorophore was almost planar, and the appended pyrrole was in the same plane with a small deviation from the mean plane. We investigated the potential use of α-acrylaldehyde 3-pyrrolyl BODIPY for sensing thiol containing amino acids such as cysteine/homocysteine (Cys/Hcy). Our studies showed that the α-acrylaldehyde- 3-pyrrolyl BODIPY was found to be useful for exclusive sensing of Cys/Hcy and to exhibit different optical signaling responses to Cys and Hcy at physiological pH in aq. CH₃CN (1 : 1 v/v, PBS) medium. The enhancement in optical properties for Cys and quenching in same properties for Hcy was attributed to different binding modes of Cys/Hcy with α-acrylaldehyde 3-pyrrolyl BODIPY.