A time-resolved electron spin resonance study of the triplet states of 1-nitronaphthalene and 1,4-dinitronaphthalene

Nonradiative Relaxation Processes and Electronically Excited States of Nitrobenzene Studied by Picosecond Time-Resolved Transient Grating Method

“…We think this fast transition comes from very large structural changes in the excited states, and the change should be related to the NO 2 group. Since the T 1 state of nitronaphthalene phosphoresces with a lifetime of 48 ms in ether−isopentane−ethanol at 77 K 26 and the triplet character is very close to the 3 ππ* state of naphthalene, the T 1 state of NB cannot be a 3 ππ* state, but the nonbonding or the σ orbital should participate in the T 1 state; that is, the structure of the T 1 state is considerably deformed from that of the ground state by the participation of these electrons from the NO 2 group. The large structural change is consistent with the very broad feature in the absorption spectrum. , Furthermore, the triplet lifetime of NB increases with decreasing the temperatures.…”

Competitive Energy and Electron-Transfer Reactions of the Triplet State of 1-Nitronaphthalene: A Laser Flash Photolysis and Time-Resolved Resonance Raman Study

“…Differences in the reactions in solvents of variable polarity may be governed by the thermodynamics of the reactions or by the nature of the triplet state of 1NN. The nature of the latter species has been the object of many hypotheses: while some authors 13-15 propose a π−π* state, sometimes with a low-lying n−π* inducing vibronic coupling, others suggest that it is π−π* with some measure of intramolecular charge-transfer character 46,47 or even that the lowest triplet is n−π* in non polar solvents and π−π* with a charge-transfer character in polar solvents. , We have recently performed 35 a TR 3 study of the triplet state of 1NN in various solvents as well as detailed ab initio calculations which showed that although the lowest triplet state is of π−π* nature, the second triplet is of n−π* type and the latter is estimated to lie less than 0.1 eV above the former in the gas phase but has a much lower dipole moment. So we may expect either some mixing between the two states or vibronic coupling in nonpolar solvents but less so in polar solvents where the π−π* polar triplet would be much more stabilized due to its dipolar nature.…”

“…Most aromatic nitro molecules are known to be nonfluorescent, and their excited states have been the subject of study for many years. − The quantum yield of triplet formation of 1-nitronaphthalene is high (0.63 in EPA at 77 K) and the buildup time constant of the T n ← T 1 absorption is fast (<25 ps in polar and nonpolar solvents). While the luminescent properties and the transient absorption of the triplet have been intensively studied, − much less is known about the radical anion of this molecule. , On the other hand trans -stilbene has been widely used as a model in studies of cis − trans CC double-bond isomerization − and the structure and dynamics of its S 1 and T 1 states, and its radical ions have been the object of a multitude of papers. − …”

“…Most aromatic nitro molecules are known to be nonfluorescent, and their excited states have been the subject of study for many years. [7][8][9] The quantum yield of triplet formation of 1-nitronaphthalene is high (0.63 in EPA at 77 K 10 ) and the buildup time constant of the T n r T 1 absorption is fast (<25 ps in polar and nonpolar solvents 11 ). While the luminescent properties and the transient absorption of the triplet have been intensively studied, [10][11][12][13][14][15] much less is known about the radical anion of this molecule.…”

The Excited Triplet State of Azoalkanes: Electron Spin Polarization and Magnetic Field Effects During Triplet-Sensitized Photolysis of trans-Azocumene in Solution

“…3) Despite some emissive p-type TM polarization of the 1-NN triplet is expected from its known zero field tensor components ( D zfs = 85.5 mT and E zfs = -5.1 mT ) and ISC rates (X:Y:Z = 0:0.55:0.45) [41], no polarization transfer to triplet AC was found (see section 2.4.5). This is in accord with the conclusion drawn previously by Tarassov, who checked an eventual polarization transfer from 1-NN triplets to a persistent nitroxide radical and did not find any perceptible transfer [42].…”