Electronic excitation spectra of radical anions of cyanoethylenes and cyanobenzenes: Symmetry adapted cluster–configuration interaction study

Abstract

Electronic excitation spectra of the radical anions of cyanoethylenes (trans-dicyanoethylene and tetracyanoethylene) and cyanobenzenes (1,2-dicyanobenzene: o-DCNB, 1,3-dicyanobenzene: m-DCNB, and 1,4-dicyanobenzene: p-DCNB) were studied by the symmetry adapted cluster-configuration interaction (SAC-CI) method. Theoretical calculations predicted positive electron affinities for all the molecules in good agreement with the experimental observations. Electronic excitation spectra of open-shell radicals is a topic that has not been studied as much as such spectra of closed-shell molecules, but this can be easily addressed using SAC-CI theory. The present paper systematically describes the calculation procedures for radical anions by investigating several basis sets, including anion diffuse and Rydberg functions. The calculated excitation energies were in good agreement with the experimental UV∕NIR (near infrared region) spectra, which had been observed by one of the present authors in 2-methyltetrahydrofuran matrix frozen to transparent glassy solids at 77 K. For p-DCNB, the SAC-CI theoretical spectrum agreed particularly well with the experimental spectrum. An extremely weak π*(SOMO) - π* excitation at 1.41 eV predicted in the present work, but had been overlooked in the previous experimental spectrum published in 1988, was confirmed to be real by a careful re-examination of the old spectrum.

Electrochemical Activation of Diverse Conventional Photoredox Catalysts Induces Potent Photoreductant Activity**

“…[30] These fundamental challenges associated with catalyst generation and turnover have resulted in only as mall collection of electron-primed photocatalytic systems being identified in the subsequent years [29,31] despite photophysical studies establishing that numerous persistent radical anions absorb visible light. [32][33][34][35][36] We envisioned that electrochemistry would offer aflexible approach to generate electron-primed photoredox catalysts as cathodic reduction is highly tunable and divided cell electrolysis excludes interfering oxidized byproducts. [37][38][39] Indeed, we previously used this approach to introduce an ovel electron-primed photocatalyst capable of reducing aryl chloride substrates with E red on par with Li 0 .…”

“…Additionally, the byproducts of catalyst activation, which are typically reactive amine radical cations and easily reduced iminium ions, must not deactivate the catalyst or interfere in subsequent steps [30] . These fundamental challenges associated with catalyst generation and turnover have resulted in only a small collection of electron‐primed photocatalytic systems being identified in the subsequent years [29, 31] despite photophysical studies establishing that numerous persistent radical anions absorb visible light [32–36] …”

Projected CAP/SAC‐CI method with smooth Voronoi potential for calculating resonance states

“…In particular, the SAC‐CI expansion can be pruned without significant loss of accuracy through a perturbation‐based selection procedure, and can in this way be applied to comparatively large systems. In relation to the present subject, the SAC‐CI method has been applied to bound electron‐attached states of molecules; for example, para ‐ and ortho ‐benzoquinones ( p ‐BQ, o ‐BQ), cyanobenzenes and nitrobenzenes, and so forth …”

Exploiting consecutive photoinduced electron transfer (ConPET) in CO2 photoreduction

“…However, it was not completely excluded out; an absorption band at a longer wavelength would probably appear out of the range of our instrument. 17 Considering an electron is delocalized in the 4CzIPN˙ − , it is anticipated that the photoexcited state 4CzIPN˙ − * is more reducing than the ground state 4CzIPN˙ − . The time-resolved emission decay at 445 nm after visible light irradiation was estimated to be 3.78 μs (Fig.…”