The triplet state of 4‐nitronaphthylamine

Abstract

Nanosecond spectroscopic and kinetic studies of 4-nitronaphthylamine (4-NOZNA) in aerated and deaerated nonpolar solvents a t room temperature show a transient species with absorption maxima a t 470 and 665 nm. The rate constant for the decay of this species in deaerated benzene is 6.7 X 105 sec-1, while in aerated benzene solutions the species is quenched by oxygen with a rate constant k = 2.0 X 109M-'-~ec-~. The transient absorption at 470 and 665 nm is assigned to the lowest triplet excited state of 4-N02NA. In polar solvents, however, electronic excitation of 4-N01NA does not lead to any detectable transient absorption between 400 and 800 nm for the temperature range of 25 to -150°C. This is attributed to lack of intersystem crossing of CNOlNA in polar solvents.

Excited-State Dynamics of Nitrated Push−Pull Molecules: The Importance of the Relative Energy of the Singlet and Triplet Manifolds

“…The long time scans taken up to 700 ps of these small residual signals do show a decay in the 2−3 ns time scale. The disappearance in such time scales of this residual absorbance is consistent with the results from Capellos et al, who observed a lack of any transient absorbance after a 20 ns pulse for NNA/methanol . This is also in agreement with Costela et al, who observed no transient species detectable with their resolution of 30 ns for NNA in ethyl acetate …”

“…This reduces the actual time resolution of these experiments to near 1 ps. In the spectra of Figure , the long-lived species observed at t > 11 ps can be clearly identified as the phosphorescent state of this molecule from a comparison with previous measurements in the nanosecond time scale in the same solvent . The signals preceding the appearance of this species must again be related to intersystem crossing and relaxation within the triplet manifold.…”

“…Nanosecond flash photolysis experiments by Capellos et al also have detected the T n ← T 1 transient absorbance of this compound in benzene and polymethyl methacrylate (PMMA) in solution at room temperature and at −150 °C. However, when the photolysis was made in methanol solution, in the time scale of nanoseconds and microseconds, no transient species was detected . In this contribution, we include the first detailed description of the femtosecond and picosecond dynamics of MNN and NNA, which clarifies the early photodynamics of both compounds, including the participation of intermediary states as well as the solvent dependence in NNA.…”

“…). − Related to their environmental photochemistry, it has been established that nitrated polycyclic aromatic hydrocarbons (NPAHs) are considerably more photoreactive than the respective unsubstituted polyaromatics. − Although several channels may contribute to NPAH’s environmental and solution photochemistry, one of the most important ones is a direct rearrangement of the −NO 2 group leading to the formation of the respective aryloxy radical (Ar−O·) and photodetachment of nitric oxide (NO·) . This channel has been observed in nitrobenzene, 9-nitroanthracene, some 10-substituted 9-nitroanthracenes, 1-nitropyrene, and 6-nitrobenzo[ a ]pyrene, ,− but not in nitronaphthalenes like the ones of the present study, where only secondary bimolecular photochemistry of the T 1 state has been observed. − , …”

Chemical Kinetics for the Oxidation of Californium(III) Ions with Select Radiation-Induced Inorganic Radicals (Cl2•– and SO4•–)

“…It is evident from the small changes in the decay rate of the Cl 2 •– radical anion with increasing Cf .1em 3 + concentration (Figure A) that this reaction is slow and energetically unfavorable. This was to be expected given the ∼1 V difference in their respective oxidation potentials in acidic aqueous solution: E °( Cf .1em 3 + ) = +3.2 V vs E °(Cl 2 •– ) = +2.13 V. , Despite this energetic difference, pseudo-first-order rate coefficients ( k ′) were derived from the mixed pseudo-first and second-order fits to the kinetic decay data shown in Figure A based on the equation Abs ∗ k X k X ∗ e false( k X t false) − 2 ∗ Abs ∗ k Y ∗ ( 1 − e ( k normalX t ) ) + B, where Abs is the initial Cl 2 •– radical anion absorption, B is the limiting product absorption (baseline shift), k X is the pseudo-first-order component (s –1 ) corresponding to the reaction of the Cf .1em 3 + ion with the Cl 2 •– radical anion (eq ), and k Y is the second-order component (M –1 s –1 ) for the corresponding disproportionation reaction shown in eq . These pseudo-first-order values were then used to calculate an overall second-order rate coefficient of k = (8.28 ± 0.61) × 10 5 M –1 s –1 ( R 2 = 0.98) for the reaction of the Cf .1em 3 + ion with the Cl 2 •– radical anion …”