Eli Zysman-Colman

Phenonium ions have played a central role in physical–organic chemistry, yet their use as strategic intermediates in synthesis remains underexplored. Here, we report a phenonium‐ion‐mediated strategy for the skeletal editing of paracyclophanes. Installation of a one‐carbon handle at the aliphatic bridge, followed by direct alcohol activation with BF ₃ ·OEt ₂ under solvolysis‐avoiding conditions, generates a paracyclophane‐derived phenonium ion that undergoes regioselective ring opening by external nucleophiles. This strategy provides modular access to functionalized higher paracyclophane homologues and tolerates S‐, N‐, C‐, selenium‐, and halide‐based nucleophiles under operationally simple, gram‐scalable conditions. The sequence can be applied iteratively and extended to double bridge expansion, while reductive desulfurization furnishes the corresponding parent hydrocarbons. Mechanistic studies combining nuclear magnetic resonance spectroscopy, kinetic analysis, stereochemical probes, and density functional theory calculations support a self‐accelerating mechanism in which product water shifts BF ₃ speciation toward BF ₃ ·H ₂ O, which assists leaving‐group departure through hydrogen‐bond donation and thereby facilitates phenonium‐ion formation. Together, these results establish paracyclophane‐derived phenonium ions as controllable intermediates for skeletal editing and provide practical access to higher paracyclophane topologies with application potential in functional materials, as exemplified by a bridge‐expanded thermally activated delayed fluorescence (TADF) emitter.

2 Abstract Despite their potential to deliver high-efficiency organic light-emitting diodes (OLEDs), those using thermally activated delayed fluorescent (TADF) emitters often suffer from a large drop in efficiency at high luminance. This effect is known as efficiency roll-off and is a longstanding issue for these devices, which has limited their commercial deployment. We have discovered that the degree of overlap between the photoluminescence (PL) and absorption spectra drives singlet exciton diffusion and is a strong predictor of the magnitude of efficiency roll-off in TADF OLEDs. This effect is especially important in OLEDs made with multiresonant (MR)-TADF materials given their intense low-energy short-range charge transfer absorption bands. MR-TADF OLEDs are very appealing due to their narrow emission spectra; however, their small Stokes shift leads to large spectral overlap and contributes to these devices showing severe efficiency roll-off. Developing TADF materials that have a larger Stokes shift whilst maintaining their bright, narrow emission would help minimize efficiency roll-off while securing high internal quantum efficiencies, features particularly relevant for displays.

2 Abstract Despite their potential to deliver high-efficiency organic light-emitting diodes (OLEDs), those using thermally activated delayed fluorescent (TADF) emitters often suffer from a large drop in efficiency at high luminance. This effect is known as efficiency roll-off and is a longstanding issue for these devices, which has limited their commercial deployment. We have discovered that the degree of overlap between the photoluminescence (PL) and absorption spectra drives singlet exciton diffusion and is a strong predictor of the magnitude of efficiency roll-off in TADF OLEDs. This effect is especially important in OLEDs made with multiresonant (MR)-TADF materials given their intense low-energy short-range charge transfer absorption bands. MR-TADF OLEDs are very appealing due to their narrow emission spectra; however, their small Stokes shift leads to large spectral overlap and contributes to these devices showing severe efficiency roll-off. Developing TADF materials that have a larger Stokes shift whilst maintaining their bright, narrow emission would help minimize efficiency roll-off while securing high internal quantum efficiencies, features particularly relevant for displays.

Controlling conformation distributions is the key to manipulate material properties of multi-conformal molecules. Distinct from previous strategy with direct change or impact on the flexible groups, we tune the conformation distribution through changing peripheral groups to influence their intermolecular interactions. Two blue violet TADF emitters, namely tert -butyl substituted 5-(2,12-di-tert-butyl-5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracen-7-yl)−10,10-diphenyl-5,10-dihydrodibenzo[b,e][1,4]azagermine (TDBA-PAG) and cumenyl substituted 5-(2,12-bis(2-phenylpropan-2-yl)−5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracen-7-yl)−10,10-diphenyl-5,10-dihydrodibenzo[b,e][1,4]azagermine (TPDBA-PAG) were designed and synthesized. With the same germanium-integrated donor, the two compounds show similar emission properties in solution with calculated conformation dominantly of their quasi-axial (QA) forms (> 97%). However, TPDBA-PAG presents a lower QA ratio compared with TDBA-PAG, which endows the former with more pronounced TADF emission, higher emission efficiency and reduced concentration quenching phenomena in solid state. As a result, TPDBA-PAG performed as one of the best non-doped and doped violet-blue emitters and successfully sensitized MesB-DIDOBNA-N to achieve record high EQE _max of 24.7% at 406 nm, making significant progress in NUV OLEDs.

We report the first examples of chiral MR-TADF dendrimers using an intramolecular FRET design. Tuning the acceptor reveals a trade-off between CPL and device efficiency. This design allows for selecting either CPL activity or high device efficiency.

Attaining precise control of emission within the blue spectral region remains inherently challenging for ladder‐type π‐extended multiresonant thermally activated delayed fluorescent (MR‐TADF) compounds, despite their many advantageous design features. Here, we aim to address the undesired redshifting of the emission in ladder‐type MR‐TADF compounds by incorporating terminal fused carbazoles. We report two MR‐TADF compounds, B2N3 and B3N3 , the latter of which is a p‐ and n‐doped heptacene polycyclic aromatic π‐hydrocarbon (PAH), both of which contain fused carbazoles at both ends of the molecule. Relative to the previously reported MR‐TADF compound α ‐3BNMes , the emission of B3N3 is blueshifted and narrower, emitting at λ _PL of 427 nm and having a full width at half maximum (FWHM) of 25 nm in toluene. In contrast, B2N3 , which is more conformationally flexible, emits at λ _PL of 441 nm and has a FWHM of 32 nm in toluene. Sensitized organic light‐emitting diodes (OLEDs) using B2N3 and B3N3 as terminal emitters showed EQE _max of 12.8% and 10.7% emitting with CIE coordinates of (0.15, 0.10) and (0.16, 0.09), respectively.

This work highlights how the fusion of double carbonyl/amine MR-TADF emitters with different aromatic cores tunes their photophysical properties.

Solvent arguably constitutes the single largest waste stream in synthesis. Mechanophotocatalysis , a synergistic union of mechanochemistry and photocatalysis, offers a solution to significantly reduce solvent use in photochemistry. Here, we show how photochemical reactions in the solid state can be driven by visible light using in situ formed electron donor–acceptor (EDA) complexes in air, obviating the need for an external photocatalyst. Under the optimized conditions, only 2–4 equiv. of solvent is used as a liquid‐assisted grinding (LAG) agent, thus significantly reducing solvent use. We demonstrate EDA mechanophotochemistry across five reactions: a Giese reaction; a C─S cross‐coupling reaction; a phosphorylation reaction; a sulfonylation reaction; and a Povarov reaction. While the first four proceeded readily and competitively with the solution‐state EDA photochemical reaction, the latter one, requiring O ₂ as a terminal oxidant, does not. In investigating the sulfonylation reaction we further identify the first example of a photomechanoredox reaction in which the stainless‐steel milling ball directly participates in the reaction, revealing the milling medium as a previously unrecognized reactivity parameter. Together, these results establish visible light‐promoted mechanophotochemistry as a solvent‐minimized and viable alternative to solution‐state photochemical reactions.

Solvent arguably constitutes the single largest waste stream in synthesis. Mechanophotocatalysis , a synergistic union of mechanochemistry and photocatalysis, offers a solution to significantly reduce solvent use in photochemistry. Here, we show how photochemical reactions in the solid state can be driven by visible light using in situ formed electron donor–acceptor (EDA) complexes in air, obviating the need for an external photocatalyst. Under the optimized conditions, only 2–4 equiv. of solvent is used as a liquid‐assisted grinding (LAG) agent, thus significantly reducing solvent use. We demonstrate EDA mechanophotochemistry across five reactions: a Giese reaction; a C─S cross‐coupling reaction; a phosphorylation reaction; a sulfonylation reaction; and a Povarov reaction. While the first four proceeded readily and competitively with the solution‐state EDA photochemical reaction, the latter one, requiring O ₂ as a terminal oxidant, does not. In investigating the sulfonylation reaction we further identify the first example of a photomechanoredox reaction in which the stainless‐steel milling ball directly participates in the reaction, revealing the milling medium as a previously unrecognized reactivity parameter. Together, these results establish visible light‐promoted mechanophotochemistry as a solvent‐minimized and viable alternative to solution‐state photochemical reactions.

Here, we report a mild, light-assisted iridium-catalyzed C–H borylation protocol for organic substrates. We demonstrate that adapting the Ishiyama–Tagaki–Miyaura–Hartwig (ITMH) protocol for C–H borylation to proceed under photochemical conditions imparts a pronounced rate enhancement compared to the established dark reaction. This photochemistry methodology achieves higher yields across a broad range of substrates and is easily scalable using continuous flow technology.