(Co)oxidation/cyclization processes upon irradiation of triphenylamine

The Photoinduced Electrocyclization Reaction of Triphenylamine (TPA) in Sustainable and Confined Micellar Solutions: A Steady‐State and Laser Flash Photolysis Approach

“…Irradiation of TPA in N 2 ‐saturated acetonitrile solutions with a laser pulse (355 nm) provides the absorption spectra of a transient which shows two characteristic bands with maximum wavelengths located at 400 and 625 nm (see Figure 3(a)) and the spectra was attributed to the N‐phenyl‐ 4a,4b ‐dihydrocarbazole (DHC 0 ) transient in agreement with the literature [26,32] . A similar behavior was observed in cyclohexane and methanol (see Figure S3 in SI).…”

“…Once formed, DHC 0 undergoes competitive deactivation pathway in inert atmosphere, viz. back‐electrocyclization to TPA (pathway k’ d ) and disproportionation reaction ( k R ) to give N ‐phenyl carbazole (N−PhCA) and N ‐phenyl‐tetrahydrocarbazole (N‐PhTHCA) as the main photoproducts [26] . On the other hand, when the time‐resolved experiment of TPA in O 2 ‐saturated solutions was performed under oxygen atmosphere a new intermediate hydroperoxide A is formed with a rate constant k O2 that finally evolved to give N‐phenyl carbazole as the sole photoproduct along with hydrogen peroxide.…”

“…Furthermore, the relative profiles of NÀ PhCA formation measured in both acetonitrile and methanol solutions are similar, whereas in hexane the formation of NÀ PhCA proceeded slowly. This kinetic behavior suggests that non-polar solvents such as hexane, favor the deactivation of 3 TPA, [26] which is the photo reactive excited state, through a nonradiative decay rate that competes in some extent with the photoinduced electrocyclization pathway. [27,28] The observed trend was quantitatively measured in terms of the rate of formation of N-phenylcarbazole (μmol min À 1 ) reported in Table 1 and it was found that the photoreaction proceeds faster in micellar solution (0.0654 μmol min À 1 ) than in cyclohexane (0.0127 μmol min À 1 ).…”

Photochemistry of Tris(2,4‐dibromophenyl)amine and its Application to Co‐oxidation on Sulfides and Phosphines†

“…A similar oxygen effect was observed for the photochemical reaction of tris( p ‐bromophenyl)amine and triphenylamine in different solvents. In the case of triphenylamine, the quenching of the triplet excited state by molecular oxygen produced singlet oxygen with a quantum yield ( ϕ Δ ) value of 0.63, which is a competitive pathway of the electrocyclization reaction (24). Therefore, the photoreaction of triphenylamine is faster than that of tris( p ‐bromophenyl)amine and the photoreaction of this latter substrate is faster than that of 1 (see Fig.…”

“…These bands were assigned to the UV‐visible absorption spectra of two transient species, viz. radical cation 1 ·+ and radical cation polybromosubstituted dihydrocarbazole ( 2 ·+ ) (see Scheme 2) (23,24). A similar behavior was observed when the experiments were performed under O 2 atmosphere.…”