Laser flash photolysis study of the photoinduced oxidation of 4-(dimethylamino)benzonitrile (DMABN)

Abstract

The radical cation of DMABN was investigated as a model intermediate to understand the photodegradation of anilines in surface waters.

Quenching of an Aniline Radical Cation by Dissolved Organic Matter and Phenols: A Laser Flash Photolysis Study

“…Excitation of 2-AN or 1-NA in the presence of phenol yields their excited triplet states, with absorption maxima at ≈440 nm (Figure 2A) and ≈510 nm (Figure 2C), respectively. 25 The evolution of the triplet state spectra in the presence of phenol is almost identical compared to a solution containing the photosensitizers alone, 25 reflecting the very low triplet quenching rate constants by phenol (3.3 × 10 7 M −1 s −1 for 3 2-AN* 29 and 5 × 10 7 M −1 s −1 for 3 1-NA*, see Table 1). The only found difference consist in the appearance of weak absorption features in the wavelength range of 390 − 460 nm at longer delay times after the laser pulse.…”

“…However, a large increase in the second-order rate constants occurs when 𝐸𝐸 ox 0 increases from ˗1.38 to ˗1.23 V vs. standard hydrogen electrode (SHE) (the 𝐸𝐸 ox 0 values for 4-methylphenol and 4-methoxyphenol, respectively). The negative value of the standard oneelectron reduction potential of DMABN (1.30 ± 0.07 V vs. SHE, taken as the average of two values recently estimated from excited triplet quenching data using a Rehm-Weller relationship), 25 falls near the middle of the range in which the jump in second-order rate constant occurs. Consequently, a pure electron transfer reaction of the type:…”

“…Nanosecond laser flash photolysis experiments using pulses of ≤ 170 ps duration from a Nd:YAG laser were conducted as detailed elsewhere. 25 The observation wavelengths of the different transient species are given in the SI, Table S2.…”

“…Despite the large uncertainty, this value is very close to the value of 1.30 ± 0.07 V vs. SHE for 𝐸𝐸 red 0 (DMABN ⦁+ /DMABN) determined in a preceding study. 25 In a second step, we characterized the species involved in the reductive quenching of the excited triplet state of 1-NA by SDZ (see SI, Text S5 and Figure S7). The reaction of SDZ with the excited triplet state of two photosensitizers produced a broad transient absorption spectrum centered at ≈430 nm attributed to SDZ •− , the radical resulting from deprotonation of SDZ • according to a previous quantum chemical computation study.…”

Femto- to Millisecond Time-Resolved Photodynamics of a Double-Functionalized Push–Pull Organic Linker: Potential Candidate for Optoelectronically Active MOFs

“…The existence of a T 1 state has been previously reported for the non-functionalized (NDC) and the monofunctionalized (NADC) molecules, having both the same naphthalene dicarboxylate core structure [ 20 ]. It has been also described for DMABN, whose central core is a benzene ring instead of naphthalene, but which is double functionalized with an amino and carbonitrile groups, similar to Me 2 CANADC [ 51 , 52 , 53 , 54 ]. On the other hand, the longest τ 2 component is unaffected by the presence of oxygen and exhibits a similar value of approximately 2 µs in all the studied solvents and environments ( Table 4 ).…”