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While a great number of C–H functionalization methods have been developed in recent years, new mechanistic paradigms to deconstruct such bonds have been comparatively rare. Amongst possible strategies for breaking a C<i>_sp³</i>–H bond are deprotonation, oxidative addition with a metal catalyst, direct insertion via a nitrene intermediate, hydrogen atom transfer (HAT) with both organic and metal-based abstractors, and lastly, hydride abstraction. The latter is a relatively unexplored approach due to the unfavorable thermodynamics of such an event, and thus has not been developed as a general way to target both activated and unactivated C<i>_sp³</i>–H bonds on hydrocarbon substrates. Herein, we report our successful efforts in establishing a catalytic C–H functionalization manifold for accessing an intermediate carbocation by formally abstracting hydride from unactivated C<i>_sp³</i>–H bonds. The novel catalytic design relies on a stepwise strategy driven by visible light photoredox catalysis and is demonstrated in the context of a C–H fluorination employing nucleophilic fluorine sources. Difluorination of methylene groups is also demonstrated, and represents the first C–H difluorination with nucleophilic fluoride. Additionally, the formal hydride abstraction is shown to be amenable to several other classes of nucleophiles, allowing for the construction of C–C or C–heteroatom bonds.

Covalently attached perylene monolayers serve as back contacts for Sb 2 S 3 photoelectrochemical cells with a thianthrene +/0 front, rectifying contact. Covalent attachment of perylenetetracarboxylic dianhydride, PTCDA, to Si(111) utilizes an anhydride-to-imide conversion at surface-attached amines. For Sb 2 S 3 solar absorbers, we hypothesized that a terminal thioperylene anhydride, i.e., S=C–O–C=S, formed from thionation of the terminal perylene anhydride would serve as a soft, electron-selective and hole-blocking back contact. We explored several routes to convert carbonyls to thiocarbonyls on surface-attached perylene anhydrides including Lawesson’s reagent, P 4 S 10 , and a P 4 S 10 –pyridine complex. Here, P 4 S 10 in toluene yielded the highest conversion as quantified by thioperylene-anhydride-S-to-imide-N ratios in X-ray photoelectron spectroscopy (XPS). Spectra demonstrated minimal residual reagent as determined by the absence of quantifiable phosphorus following sonication and rinsing. Photoelectrochemistry yielded an average | V oc | = 840 ± 90 mV with the highest value of 952 mV under ELH-simulated AM1.5G illumination for chemical-bath-deposited Sb 2 S 3 in the strongly oxidizing thianthrene +/0 redox couple when thioperylene-anhydride-tethered surfaces formed the back contact. Sb 2 S 3 absorbers in which perylene anhydride, esters, thionoesters, and thiols form the back contact yielded significantly decreased | V oc | magnitudes vs Sb 2 S 3 on perylene-thioanhydride-terminated surfaces. We attribute the large V oc to the combination of favorable sulfur-functionalized surfaces for deposition, charge transfer properties of the perylene layer, and use of the thianthrene +/0 redox couple.