engleski

Photophysical properties and electron transfer photochemical reactivity of substituted phthalimides

Photochemical reactivity, photophysical and electrochemical properties for a series of N- adamantylphthalimides bearing carboxylic functional groups were investigated. Upon irradiations (with or without a triplet sensitizer), compounds undergo decarboxylation via a photoinduced electron transfer (PET) from the carboxylate to the phthalimide. UV-Vis and fluorescence pH titrations were used to determine pKa values for the prototropic forms, which were put in connection with quantum yields of the reaction (ΦR). Compounds bearing electron donors OH and OCH3 at the phthalimide 4 position are fluorescent (ΦF = 0.02-0.49) and PET takes place from both singlet and triplet excited states. Estimated rate constants for PET in the singlet excited states for methoxy- and amino-substituted phthalimides are (2.0 ± 0.1) × 109 s-1and (3.4 ± 1.0) × 107 s-1, respectively. Laser flash photolysis (LFP) was conducted to characterize triplet excited states, which are populated less efficiently for compounds with electron donors. The PET is reversible and the overall ΦR depends on the rates for back electron transfer, protonation of the phthalimide radical anion and decarboxylation. Plausible photochemical and photophysical pathways depend on the phthalimide substituents, which is important for the use of phthalimide derivatives in organic synthesis and photocatalysis.

phthalimides ; photodecarboxylation ; photoinduced electron transfer ; photophysics

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