Spectroscopic and ¹O₂ Sensitization Characteristics of a Series of Isomeric Re(bpy)(CO)₃Cl Complexes Bearing Pendant BODIPY Chromophores

Abstract

Two new Re(I)bipyridyltricarbonylchloride complexes, Re(BB3)(CO) 3 Cl, and Re(BB4)(CO) 3 Cl, featuring BODIPY groups appended to the 5,5'-, or 6,6'-positions of the bipyridine ligand respectively, have been synthesized as structurally isomeric compliments to a previously reported 4,4'-substituted homologue, Re(BB2)(CO) 3 Cl. X-ray crystal structures of the compounds show that the 4,4'-, 5,5'-and 6,6'-substitution patterns place the BODIPY groups at progressively shorter distances of 9.43 Å, 8.39 Å and 5.56 Å, respectively, from the complexes' Re centers. The photophysical properties of the isomeric complexes were investigated to ascertain the manner in which the heavy rhenium atom might induce intersystem crossing of the pendant BODIPY moieties positioned at progressively shorter through-space distances. Electronic absorption spectroscopy revealed that the three metal complexes retain the strong visible absorption features characteristic of the bpy-BODIPY (BB2-BB4) ligands, however, the fluorescence of the parent borondipyrromethane appended ligands is attenuated by more than an order of magnitude in Re(BB2)(CO) 3 Cl and Re(BB3)(CO) 3 Cl, and by more than two orders of magnitude in Re(BB4) (CO) 3 Cl. Furthermore, phosphorescence from Re(BB4)(CO) 3 Cl is observed under a nitrogen atmosphere, consistent with highly efficient ISC to the triplet-excited state. Singlet oxygen sensitization studies confirm that all three complexes produce singlet oxygen with quantum yields that increase as the distance of the BODIPY groups to the heavy rhenium center is decreased. The trends observed across the series of rhenium complexes with respect to emission and 1 O 2 sensitization properties can be rationalized in terms of the varied distal separation between the metal center and BODIPY groups in each system.

Cyclometalated iridium–BODIPY ratiometric O2 sensors

“…The large attenuation of ε in the piq series is reproducible over multiple samples, though the origin is not clear. Such an effect has not been previously observed in other 5d metal complexes linked to BODIPY through the meso position 54,68–72. The UV and near-visible regions involve several overlapping bands, attributed to a combination of π → π* transitions involving the BODIPY (compare to Fig.…”

“…Such an effect has not been previously observed in other 5d metal complexes linked to BODIPY through the meso position. 54,[68][69][70][71][72] The UV and nearvisible regions involve several overlapping bands, attributed to a combination of p / p* transitions involving the BODIPY (compare to Fig. S19 †), and the expected bands 73 from the [Ir(C^N) 2 ] + fragment that include C^N-centered p / p* transitions at higher energy and MLCT transitions at lower energy.…”

Computational Design of Rhenium(I) Carbonyl Complexes for Anticancer Photodynamic Therapy

“… 22 − 25 As a result, there is great interest in modifying the existing PSs or developing new classes of PSs. Among the latter, rhenium(I) tricarbonyl complexes have been explored in recent years as potential candidates for PDT 26 − 35 due to their rich photophysical and biochemical properties, including polarized emission, high photostability, large Stokes shifts, triplet states with long lifetimes, and biocompatibility, 36 − 40 which can also be tuned by varying the ligands.…”

Photodynamic therapy applications of Re(I)‐BODIPY functionalized nanoparticles

“…[ 11 ] Boron‐dipyrromethene (BODIPY) is considered as a suitable chromophore for complexation to organometallic rhenium core owing to the ease of synthesis and their tunable absorption profile in the visible and NIR region. [ 11,12 ] It was recently reported that two Re(I)‐BODIPY complexes containing ethynyl moieties with enhanced π‐conjugation between chromophore and Re(I) center exhibited absorption in the green region. Efficient intersystem crossing (ISC) was observed in these complexes with triplet state lifetimes of 104 and 127 μs, thereby favoring photosensitized generation of singlet oxygen with quantum yields of Φ Δ = 0.88 and 0.06.…”

“…[ 11 ] In another example, a few Re(I)‐bipyridine complexes were prepared, wherein the BODIPY chromophores were attached at varying distances (∼5–10 Å from the metal center), and a relation between 1 O 2 sensitization property and the Re‐BODIPY distal separation was established. [ 12a ] Despite the fact that the photophysical and photosesitization properties of several Re(I)‐BODIPY complexes have been the subject of numerous investigations, their (in vitro/in vivo) biological applications have received limited attention. [ 12d ]…”