Preparation, Characterization, Redox, and Photoinduced Electron‐Transfer Properties of the NIR‐Absorbing N‐Ferrocenyl‐2‐pyridone BODIPYs

Abstract

Mono-and di-(N-ferrocenyl-2-pyridone)-containing BODIPYs were prepared using a set of ferrocene-enamine cyclization reactions. The target compounds were characterized by UV-Vis, NMR, and mass spectrometry, while their redox properties were probed by the electrochemical, spectroelectrochemical, and chemical oxidation methods. Redox properties of the di-(ferrocenyl)-containing BODIPY are suggestive of a lack of electronic coupling between the two ferrocene groups. Oxid-

Photophysics, Redox Processes, and Electronic Structures of Ferrocenyl-Containing BODIPYs, aza-BODIPYs, BOPHYs, Transition-Metal Dipyrromethenes and aza-Dipyrromethenes

“…Oxidation of the ferrocene substituent(s) in BODIPYs and their analogues under chemical or spectroelectrochemical oxidation conditions reduces the effectiveness of such electron-transfer pathway and results in partial restoration of the fluorescence, which can be again suppressed by the reduction of ferricinium group to ferrocene (Figure 10). [7,10,11,16,17,25,29,33] Similar partial restoration of the steady-state fluorescence was also reported for ferrocene-containing BODIPY system in viscous solvents [32] and upon addition of water [28] to a solution of some ferrocene-containing BODIPYs. It was speculated that the dihedral angle (and thus degree of conjugation between ferrocene group and chromophore's π-system) is responsible for the fluorescence increase in the former case, while partial degradation of the organometallic fragment is responsible for fluorescence increase in the latter.…”

“…In the most of case, DFT and TDDFT calculations using standard hybrid (20 % of Hartree-Fock exchange) B3LYP exchange-correlation functional coupled with doubleor triple-ζ quality basis sets provide a good agreement between theoretical and experimental data. [6][7][8][9]11,13,16,19,21,[23][24][25]29,32,35] In several cases of the ferrocenyl-containing azaBODIPYs and BOPHY, however, it was shown that use of the hybrid TPSSh (10 % of Hartree-Fock exchange) results in better correlation between theoretical and experimental data. Modified from reference [6] .…”

“…[7,12,14,17,[19][20][21]23] In these cases, the ferrocene fragments are electronically decoupled from the BODIPY's or aza-BODIPY's π-system, and to a large extent have independent behavior. For all cases, the DFT-predicted HOMOs are entirely or almost entirely localized at the ferrocene fragments, while the LUMOs are pure BODIPY's or aza-BODIPY's centered orbitals.…”

“…Typical partial restoration of fluorescence in ferrocenyl-containing BODIPYs. Modified from reference [7] . Figure 11.…”

“…The one exception in this group is compound 68 in which the DFT-predicted HOMO is highly delocalized between organometallic fragments and BODIPY core. [7] The electronic structures of the transition-metal dipyrromethenes 76-87 were not investigated by DFT calculations. [36][37][38] Nevertheless, based on available electrochemical data on some of these compounds, one might expect that the HOMO in these systems should be ferrocene-centered, which is similar to the compounds described above.…”