Toward Organic Photohydrides: Excited-State Behavior of 10-Methyl-9-phenyl-9,10-dihydroacridine

Abstract

The excited-state hydride release from 10-methyl-9-phenyl-9,10-dihydroacridine (PhAcrH) was investigated using steady-state and time-resolved UV/vis absorption spectroscopy. Upon excitation, PhAcrH is oxidized to the corresponding iminium ion (PhAcr(+)), while the solvent (acetonitrile/water mixture) is reduced (52% of PhAcr(+) and 2.5% of hydrogen is formed). The hydride release occurs from the triplet excited state by a stepwise electron/hydrogen-atom transfer mechanism. To facilitate the search for improved organic photohydrides that exhibit a concerted mechanism, a computational methodology is presented that evaluates the thermodynamic parameters for the hydride ion, hydrogen atom, and electron release from organic hydrides.

A Bioinspired Disulfide/Dithiol Redox Switch in a Rhenium Complex as Proton, H Atom, and Hydride Transfer Reagent

“…Subsequently, we probed the 1H + /2e – reactivity of 1 H – with two different hydride acceptors. The reaction of in situ generated 1 H – with 1.0 equiv of the acridinium hydride acceptor Ph-Acr + at 25 °C in MeCN- d 3 afforded 1 concomitant with the formation of Ph-AcrH (Figure and Figure S28; [Ph-Acr]­ClO 4 = 10-methyl-9-phenyl­acridinium perchlorate, Δ G ° H – = 76 kcal mol –1 in MeCN) . Monitoring of the reaction progress by 1 H NMR spectroscopy using the internal standard 1,3,5-trimethoxy­benzene showed that the reaction was almost completed after 3 h at 25 °C and proceeds with 90% spectroscopic yield (Figure S22).…”

Modern Spin on the Electrochemical Persistence of Heteroatom-Bridged Triphenylmethyl-Type Radicals

“…The radical [XNCH 3 ] • in Figure S26a displays strong enough red-shifted absorption bands relative to its triflate salt [XNCH 3 ] + to color the cuvette solution orange and weak absorption bands past 550 nm. 27,32 The accumulation of orange-colored [XNCH 3 ] • can be reproduced by addition of either metallic Zn or SmI 2 /THF under Ar. The SEC of [X O] + and [XS] + in Figure S26b,c produces blue-shifted absorption bands relative to their triflate salts and similar weak absorption bands past 550 nm.…”

“…In the nearly 100 years since that time, these radicals have been implicated as intermediates in numerous systems for the study of potential NADH/NAD + analogues, , catalytic photo-oxidants, and hydrogen evolution catalysts . Their one-electron oxidized counterparts, the cations 10-methyl-9-phenylacridinium [ XNCH 3 ] + , 9-phenylxanthenium [ XO ] + , and 9-phenylthioxanthenium [ XS ] + , shown in Scheme , are interesting in their own rights as intermediates in turn-on fluorescent photo- and electrochromic switches, − excited-state photohydrides and photobases. , …”

“…With the understanding that dissolved O 2 alone impacted the longevity of the radicals [ XNCH 3 ] • , [ XO ] • , and [ XS ] • at conventional time scales, spectroelectrochemistry (SEC) was conducted to collect their UV–visible absorption spectra by holding the potential near the cation/radical redox couples. The radical [ XNCH 3 ] • in Figure S26a displays strong enough red-shifted absorption bands relative to its triflate salt [ XNCH 3 ] + to color the cuvette solution orange and weak absorption bands past 550 nm. , The accumulation of orange-colored [XNCH 3 ] • can be reproduced by addition of either metallic Zn or SmI 2 /THF under Ar. The SEC of [ XO ] + and [ XS ] + in Figure S26b,c produces blue-shifted absorption bands relative to their triflate salts and similar weak absorption bands past 550 nm.…”

Benchmarking Density Functionals, Basis Sets, and Solvent Models in Predicting Thermodynamic Hydricities of Organic Hydrides

“…meaning it measures the free energy difference before and after a hydride transfer reaction. Hydride transfer reactions play a crucial role in various renewable energy technologies, such as the electrochemical reduction of CO 2 into carbon-based fuels [1,2,3,4,5,6] or H 2 synthesis [4,7].…”