Front Matter

Arecchi, Angelo V.; Messadi, Tahar; Koshel, R. John

doi:10.1117/3.764682.fm

Cited by 2 publications

(2 citation statements)

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“…While LED irradiation centered at 400 nm was empirically determined to afford optimal yields for the ring contraction, the substrates do not absorb strongly at 400 nm, with UV–Vis analysis revealing that λ max for the spatially forbidden n → π* absorbance is typically at higher energy wavelengths (330–370 nm, Figure , see SI section 5 for details). Because LEDs are not highly monochromatic light sources (for example, compared to lasers), ,, the Penn PhD m2 photoreactor used to run the ring contractions with a 400 nm LED insert emits across a relatively broad range of wavelengths (see SI section 7 for measurement of an emission spectrum). As such, one rationalization for the use of 400 nm LED irradiation, despite the relatively poor substrate absorbance, could be that the ring contraction is simply promoted by a small percentage of higher energy photons from the short-wavelength tail of the emission spectrum.…”

Section: Resultsmentioning

confidence: 99%

Mechanistic Investigation, Wavelength-Dependent Reactivity, and Expanded Reactivity of N–Aryl Azacycle Photomediated Ring Contractions

Kim,

Schwarz,

Jurczyk

et al. 2024

J. Am. Chem. Soc.

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Under mild blue-light irradiation, α-acylated saturated heterocycles undergo a photomediated one-atom ring contraction that extrudes a heteroatom from the cyclic core. However, for nitrogenous heterocycles, this powerful skeletal edit has been limited to substrates bearing electron-withdrawing substituents on nitrogen. Moreover, the mechanism and wavelength-dependent efficiency of this transformation have remained unclear. In this work, we increased the electron richness of nitrogen in saturated azacycles to improve light absorption and strengthen critical intramolecular hydrogen bonding while enabling the direct installation of the photoreactive handle. As a result, a broadly expanded substrate scope, including underexplored electron-rich substrates and previously unsuccessful heterocycles, has now been achieved. The significantly improved yields and diastereoselectivities have facilitated reaction rate, kinetic isotope effect (KIE), and quenching studies, in addition to the determination of quantum yields. Guided by these studies, we propose a revised ET/PT mechanism for the ring contraction, which is additionally corroborated by computational characterization of the lowest-energy excited states of α-acylated substrates through time-dependent DFT. The efficiency of the ring contraction at wavelengths longer than those strongly absorbed by the substrates was investigated through wavelength-dependent rate measurements, which revealed a red shift of the photochemical action plot relative to substrate absorbance. The elucidated mechanistic and photophysical details effectively rationalize empirical observations, including additive effects, that were previously poorly understood. Our findings not only demonstrate enhanced synthetic utility of the photomediated ring contraction and shed light on mechanistic details but may also offer valuable guidance for understanding wavelength-dependent reactivity for related photochemical systems.

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Section: Resultsmentioning

confidence: 99%

Mechanistic Investigation, Wavelength-Dependent Reactivity, and Expanded Reactivity of N–Aryl Azacycle Photomediated Ring Contractions

Kim,

Schwarz,

Jurczyk

et al. 2024

J. Am. Chem. Soc.

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“…It should be noted that the backward rays pass through the SLM pixels at an angle, while the forward rays are horizontal. This characteristic can be explained by considering the properties of Köhler illumination, since BONN can be considered as a modified version of LCOE, which is based on Köhler illumination [ 20 , 21 ]. In BONN, lenses 2 and 3 form a projection system where the SLM and the second substrate are conjugate.…”

Section: Methodsmentioning

confidence: 99%

Bidirectional Optical Neural Networks Based on Free-Space Optics Using Lens Arrays and Spatial Light Modulator

2024

Micromachines

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This paper introduces a novel architecture—bidirectional optical neural network (BONN)—for providing backward connections alongside forward connections in artificial neural networks (ANNs). BONN incorporates laser diodes and photodiodes and exploits the properties of Köhler illumination to establish optical channels for backward directions. Thus, it has bidirectional functionality that is crucial for algorithms such as the backpropagation algorithm. BONN has a scaling limit of 96 × 96 for input and output arrays, and a throughput of 8.5 × 1015 MAC/s. While BONN’s throughput may rise with additional layers for continuous input, limitations emerge in the backpropagation algorithm, as its throughput does not scale with layer count. The successful BONN-based implementation of the backpropagation algorithm requires the development of a fast spatial light modulator to accommodate frequent data flow changes. A two-mirror-like BONN and its cascaded extension are alternatives for multilayer emulation, and they help save hardware space and increase the parallel throughput for inference. An investigation into the application of the clustering technique to BONN revealed its potential to help overcome scaling limits and to provide full interconnections for backward directions between doubled input and output ports. BONN’s bidirectional nature holds promise for enhancing supervised learning in ANNs and increasing hardware compactness.

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Front Matter

Cited by 2 publications

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Mechanistic Investigation, Wavelength-Dependent Reactivity, and Expanded Reactivity of N–Aryl Azacycle Photomediated Ring Contractions

Mechanistic Investigation, Wavelength-Dependent Reactivity, and Expanded Reactivity of N–Aryl Azacycle Photomediated Ring Contractions

Bidirectional Optical Neural Networks Based on Free-Space Optics Using Lens Arrays and Spatial Light Modulator

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