Reductive N−O bond cleavage has been widely explored for providing either N or O radical species for various coupling processes. Despite significant advances, this photoredox pathway is less appealing due to poor atom economy owing to the loss of one fragment during the transformation. In this regard, the homolytic N−O bond cleavage by an energy-transfer pathway to provide two key radicals would be highly desirable for overcoming the limitations of the use of one fragment. We report an exclusive energy-transfer approach for the development of a challenging radical−radical C(sp 3 )− N cross-coupling process by reactivity-tuning of the catalytic system. The homolytic N−O bond cleavage of oxime esters in the presence of an Ir complex produces acyloxy and iminyl radicals, which undergo decarboxylative cross-coupling to yield valuable imines (typically 0.25 mol % cat. and 1 h reaction time). Extensive photophysical and electrochemical measurements, as well as density functional theory studies, were carried out to probe the mechanism and the operation of a Dexter-type energy-transfer pathway was revealed. The choice of solvent (EtOAc) and reaction concentration were critical for achieving the selectivity and reactivity in this cross-coupling process. The synthetic utility of this method was explored by studying highly functionalized oxime esters, including derivatives of biologically active natural products and drug molecules. Furthermore, in situ transformations of the imine products into pharmaceutically important amines were also demonstrated, showcasing the utility of the imine products as valuable amine building blocks.

An unprecedented approach to the generation of an Ncentered radical via a photocatalytic energy-transfer process from readily available heterocyclic precursors is reported, which is distinctive of the previous electron transfer approaches. In combination with singlet oxygen, the in-situ-generated nitrogen radical from the oxadiazoline substrate in the presence of fac-Ir(ppy) 3 undergoes a selective ipso addition to arenes to furnish remotely doublefunctionalized spiro-azalactam products. The mechanistic studies provide compelling evidence that the catalytic cycle selects the energy-transfer pathway. A concurrent activation of molecular oxygen to generate singlet oxygen by energy transfer is also rationalized. Furthermore, the occurrence of the electron transfer phenomenon is excluded on the basis of the negative driving forces for one-electron transfer between oxadiazoline and the excited state of fac-Ir(ppy) 3 with a consideration of their redox potentials. The necessity of singlet oxygen as well as the photoactivated oxadiazoline substrate is clearly supported by a series of controlled experiments. Density functional studies have also been carried out to support these observations. The scope of substrates is explored by synthesizing diversely functionalized cyclohexadienone moieties in view of their utility in complex organic syntheses and as potential targets in pharmacology.

Phosphorescent Pt(II) complexes having tetradentate ligands have emerged as promising materials for use in organic light emitting devices (OLEDs). One drawback that retards the full exploitation of their electroluminescence is a strong propensity for bathochromically shifted emissions. The chromic shift results from intermolecular association. Molecular strategies that avoid the intermolecular interactions are needed, particularly for producing blue electrophosphorescence. We have designed and synthesized a series of phosphorescent cycloplatinate complexes having bis(1-pyrazolylphenyl)methane tetradentate ligands (PtSN1−3). The ligands have been systematically modified to incorporate methyl substituents at different positions of the pyrazole moieties (PtSN1, no methyl substituent; PtSN2, 4-methyl substituents; PtSN3, 3-methyl substituents) with the aim of preserving intrinsic sky-blue phosphorescence while suppressing intermolecular interactions. The synthetic modifications control the extent of out-of-plane distortions in the cycloplatinate scaffold. Excimer emission is obtained from PtSN1−2 of planar platinacycles in diluted solutions (10 μM) or in thin mCBP:TSPO1 (8 wt %) films (1:1, wt/wt; mCBP = 3,3-di(9H-carbazol-9-yl)biphenyl; TSPO1 = diphenyl(4-(triphenylsilyl)phenyl)phosphine oxide) due to strong spontaneous excimer formation with free energy changes of −4.4 to −3.1 kJ mol −1 . By contrast, helically distorted PtSN3 is capable of preserving its inherent sky-blue phosphorescence in concentrated states as it effectively suppresses excimer formation. An additional benefit of our synthetic control is improved stability against degradation for PtSN3. Finally, electroluminescence performances were evaluated by constructing and analyzing multilayer OLEDs employing the PtSN complexes as dopants. As expected, the PtSN3 devices produced sky-blue electrophosphorescence with a Commission Internationale de l'E ́clairage coordinate of (0.16, 0.24) and a peak external quantum efficiency of 8.5%. The electrophosphorescence spectra of the PtSN1−2 devices were contaminated with excimer luminescence. These results collectively demonstrated the effectiveness of the helical distortion approach for obtaining blue electrophosphorescence.

Tri­(9-anthryl)­borane was successfully applied as an organophotocatalyst for the visible-light-induced trifluoromethylation of unactivated alkenes with CF3I. The mild reaction conditions tolerated a variety of functional groups, and the reaction could be extended to perfluoroalkylations with C3F7I and C4F9I. Mechanistic studies revealed that the photoredox catalysis involves an oxidative quenching pathway.

The combined use of a singlet oxygen photosensitizer and 1,3-diarylisobenzothiophene enables efficient generation of hydrogen sulfide under visible light illumination.