Mechanistic Study of the Photochemical Hydroxide Ion Release from 9-Hydroxy-10-methyl-9-phenyl-9,10-dihydroacridine

Abstract

The excited-state behavior of 9-hydroxy-10-methyl-9-phenyl-9,10-dihydroacridine and its derivative, 9-methoxy-10-methyl-9-phenyl-9,10-dihydroacridine (AcrOR, R = H, Me), was studied via femtosecond and nanosecond UV-vis transient absorption spectroscopy. The solvent effects on C-O bond cleavage were clearly identified: a fast heterolytic cleavage (τ = 108 ps) was observed in protic solvents, while intersystem crossing was observed in aprotic solvents. Fast heterolysis generates 10-methyl-9-phenylacridinium (Acr(+)) and (-)OH, which have a long recombination lifetime (no signal decay was observed within 100 μs). AcrOH exhibits the characteristic behavior needed for its utilization as a chromophore in the pOH jump experiment.

Organic Photoredox Catalysis

“…The 9-phenyl substituted Ph-Acr-Me + showed no evidence of radical−radical reactivity at the 9-position in one study. 306 Unfortunately, Ph-Acr-Me + is subject to nucleophilic deactivation, 307 and, furthermore, possesses a drastically shorter singlet lifetime (∼2.0 ns) and low quantum yield of fluorescence (ϕ f < 0.09) 66 due to nonradiative decay pathways related to the rotational flexibility of the phenyl substituent. 308 In other 9-aryl-substituted acridiniums where the aryl substituent is sufficiently electron rich, intramolecular electron transfer can occur in the first singlet excited state localized on the acridinium (termed "locally excited" or LE) to form a charge transfer (CT) state (also called a charge shift state).…”

Novel Oxidative Ugi Reaction for the Synthesis of Highly Active, Visible‐Light, Imide‐Acridinium Organophotocatalysts

“…In addition, they show good quantum yields in some reactions and extremely long lifetime of fluorescence . However, the first generation of this group of photocatalysts, unsubstituted or C9‐aryl substituted N ‐methyl acridinium ions (type I ), has only found limited use due to its susceptibility to the nucleophile addition at the 9‐position in the ground state, or by the addition of radical species to its corresponding acridinyl radical (Figure , I and II respectively) . In order to avoid this drawback, in 2004 Fukuzumi introduced a mesityl group at the C9‐position.…”

“…[4d, 5] However,t he first generation of this group of photocatalysts,u nsubstituted or C9-aryl substituted N-methyla cridinium ions (type I), has only found limited use due to its susceptibility to the nucleophile addition at the 9-position in the ground state, or by the addition of radical speciest oi ts corresponding acridinyl radical (Figure 1, I and II respectively). [6,7] In order to avoid this drawback, in 2004 Fukuzumi introduced am esityl group at the C9position. Therefore, the stabilityo ft he photocatalyst under the reactionc onditions was increased by blocking the access of the nucleophiles and radicals pecies to the photocatalyst (Figure 1 III).…”

Photoacidic and Photobasic Behavior of Transition Metal Compounds with Carboxylic Acid Group(s)

“…New transition metal compounds that vectorially transfer both protons and electrons are hence of interest for applications in DSSCs and other artificial photosynthetic devices. 10,[17][18][19]102 ■ CONCLUSIONS Ruthenium polypyridyl compounds were made photobasic or photoacidic through control of the orientation of the charge transfer excited state relative to the ligand with conjugated carboxylic acid groups. Excited states localized on the ligand with the carboxylic acid group were photobases while those localized on an alternative ligand were photoacids.…”