Modern Spin on the Electrochemical Persistence of Heteroatom-Bridged Triphenylmethyl-Type Radicals

Herein we present a clarification of the ambiguous persistence of the 10-methyl-9-phenylacridanyl, 9-phenylxanthenyl, and 9-phenylthioxanthenyl radicals in electrochemical experiments. Each of these radicals has separately been the subject of conflicting literature results for decades with publications claiming both their chemical inertness and propensity to dimerize. We assert that each radical is persistent at conventional electrochemical time scales up to several minutes based on reversible redox couples and cyclic voltammogram simulations of the radicals and their respective cations. All three radicals are rapidly consumed by aerial O₂, which lends irreversibility to the redox couples after fewer than 20 s of exposure to air. With appreciation for the O₂ sensitivity of these radicals, their electrochemically generated UV–visible absorption spectra have been acquired and matched to predictions made by TD-DFT calculations. Further, we propose that previous claims to have electrochemically measured radical–radical dimerizations have only observed reaction of these radicals with dissolved O₂

Modern Spin on the Electrochemical Persistence of Heteroatom-Bridged Triphenylmethyl-Type Radicals

Herein we present a clarification of the ambiguous persistence of the 10-methyl-9-phenylacridanyl, 9-phenylxanthenyl, and 9-phenylthioxanthenyl radicals in electrochemical experiments. Each of these radicals has separately been the subject of conflicting literature results for decades with publications claiming both their chemical inertness and propensity to dimerize. We assert that each radical is persistent at conventional electrochemical time scales up to several minutes based on reversible redox couples and cyclic voltammogram simulations of the radicals and their respective cations. All three radicals are rapidly consumed by aerial O₂, which lends irreversibility to the redox couples after fewer than 20 s of exposure to air. With appreciation for the O₂ sensitivity of these radicals, their electrochemically generated UV–visible absorption spectra have been acquired and matched to predictions made by TD-DFT calculations. Further, we propose that previous claims to have electrochemically measured radical–radical dimerizations have only observed reaction of these radicals with dissolved O₂

Modern Spin on the Electrochemical Persistence of Heteroatom-Bridged Triphenylmethyl-Type Radicals

Herein we present a clarification of the ambiguous persistence of the 10-methyl-9-phenylacridanyl, 9-phenylxanthenyl, and 9-phenylthioxanthenyl radicals in electrochemical experiments. Each of these radicals has separately been the subject of conflicting literature results for decades with publications claiming both their chemical inertness and propensity to dimerize. We assert that each radical is persistent at conventional electrochemical time scales up to several minutes based on reversible redox couples and cyclic voltammogram simulations of the radicals and their respective cations. All three radicals are rapidly consumed by aerial O₂, which lends irreversibility to the redox couples after fewer than 20 s of exposure to air. With appreciation for the O₂ sensitivity of these radicals, their electrochemically generated UV–visible absorption spectra have been acquired and matched to predictions made by TD-DFT calculations. Further, we propose that previous claims to have electrochemically measured radical–radical dimerizations have only observed reaction of these radicals with dissolved O₂

Modern Spin on the Electrochemical Persistence of Heteroatom-Bridged Triphenylmethyl-Type Radicals

Herein we present a clarification of the ambiguous persistence of the 10-methyl-9-phenylacridanyl, 9-phenylxanthenyl, and 9-phenylthioxanthenyl radicals in electrochemical experiments. Each of these radicals has separately been the subject of conflicting literature results for decades with publications claiming both their chemical inertness and propensity to dimerize. We assert that each radical is persistent at conventional electrochemical time scales up to several minutes based on reversible redox couples and cyclic voltammogram simulations of the radicals and their respective cations. All three radicals are rapidly consumed by aerial O₂, which lends irreversibility to the redox couples after fewer than 20 s of exposure to air. With appreciation for the O₂ sensitivity of these radicals, their electrochemically generated UV–visible absorption spectra have been acquired and matched to predictions made by TD-DFT calculations. Further, we propose that previous claims to have electrochemically measured radical–radical dimerizations have only observed reaction of these radicals with dissolved O₂

Synthesis and Optical and Electronic Properties of Core-Modified 21,23-Dithiaporphyrins

Core-modified 21,23-dithiaporphyrins, <i>meso</i>-substituted with both electron-withdrawing 4-phenylcarboxylic acids and related butyl esters, and electron-donating phenyldodecyl ethers were synthesized. The porphyrins displayed broad absorbance profiles that spanned from 400 to 800 nm with molar absorptivities ranging from 2500 to 200000 M^–1 cm^–1. Electrochemical experiments showed the dithiaporphyrins undergo two consecutive, one-electron, quasi-reversible oxidations and reductions at −1.78, −1.43, 0.63, and 0.91 V versus a ferrocene/ferrocenium internal standard. Spectroelectrochemistry and cyclic voltammetry revealed the dithiaporphyrins are stable and can endure many cycles of oxidation and reduction without signs of decomposition. The electronics of the two dithiaporphyrins were similar, and DFT calculations showed the HOMO–LUMO energy difference was smaller than tetrapyrrolic porphyrin analogues. Overall, the combination of desirable electronics, namely: quasi-reversible oxidations and reductions as well as broad absorbance profiles, combined with stability, imply that these core-modified 21,23-dithiaporphyirns could be potentially used as an ambipolar material for organic electronic applications

Tuning Light Absorption in Pyrene: Synthesis and Substitution Effects of Regioisomeric Donor–Acceptor Chromophores

Three isomeric donor–acceptor (DA) chromophores based on pyrene were synthesized to study the effects of substitution pattern on intramolecular charge-transfer absorption through pyrene. These chromophores are nonfluorescent and absorb light in the long-wavelength region approaching 700 nm, making them promising light-harvesters. Their optical properties depend greatly on the substitution pattern of the donor, but their electrochemical properties are relatively unaffected

Pi-Extended Ethynyl 21,23-Dithiaporphyrins: A Synthesis and Comparative Study of Electrochemical, Optical, and Self-Assembling Properties

21,23-Dithiaporphyrins were synthesized containing pi-extending ethynyl substituents at the meso positions. These porphyrins displayed highly bathochromic and broadened absorbance profiles spanning 400–900 nm with molar absorptivities ranging from 2500 to 300,000 M^–1 cm^–1. Electrochemically, these ethynyl dithiaporphyrins undergo a single oxidation at 0.44 or 0.57 V and reduction at −1.17 or −1.08 V versus a ferrocene/ferrocenium internal standard depending on the type of functionalization appended to the ethynyl group. DFT calculations predict that the delocalization of the frontier molecular orbitals should expand onto the meso positions of the ethynyl 21,23-dithiaporphyrins; shrinking the HOMO–LUMO energy gap by destabilizing the HOMO energy. Indeed, the DFT results agree with our optical and electrochemical assessments. Finally, differential scanning calorimetry combined with cross-polarized optical microscopy and powder X-ray diffraction was used to assess the ability of these porphyrins for long-range order. For the ethynylphenyl alkoxy 21,23-dithiaporphyin, birefringent, soft-crystalline-like domains were observed by polarized microscopy, which are marginally sustained by a low-level of crystallinity detected in the XRD, suggesting that long-range ordering is possible. Overall, ethynyl 21,23-dithiaporphyrins are able to harvest much lower energy light and possess lower oxidation and reduction potentials compared to their pyrrolic analogues, which are desirable properties for applications in organic electronics