Triplet excited states of nitronaphthalenes. III. 1,4‐dinitronaphthalene

Lang

1977

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Nanosecond laser photolytic studies of 4-nitro-N,N-dimethylnaphthylamine (4-NDMNA) in nonpolar and polar solvents at room temperature show a transient species with an absorption maximum in the 500-510-nm range. This species is assigned to the lowest triplet excited state of 4-NDMNA. The absorption maximum of this state is independent of solvent polarity, and its lifetime is a function of the hydrogen donor efficiency of the solvent. In n-hexane the lifetime Ilk of the triplet state is 9.1 X 10-6 sec, while in acetonitrile l/k is 2.0 X sec. The hydrogen abstraction rate consknt k H of the triplet state with tributyl tin hydride (BusSnH) in n-hexane is 1.7 X 107M-1.sec-1, while in the case of isopropyl alcohol as hydrogen donor, k H is 4.0 X lO7M-'.sec-l. The activation energy for the hydrogen abstraction by the triplet state from BusSnH in deaerated n-hexane is 0.6 kcal/mol. The lack of spectral shift with increasing solvent polarity, and the appreciable hydrogen abstraction reactivity of the triplet state, also independent of solvent polarity, seem to indicate that this excited state is an n-r* state which retains its n-r* character even in polar media.

Section: Assignment Of the Triplet Statementioning

confidence: 99%

“…In the case of 1,4-dinitronaphthalene [4], however, due to the symmetry of nitrosubstitution, the triplet excited state retains its n-r* character even in polar solvents.…”

Section: Introductionmentioning

confidence: 99%

The triplet state of 4‐nitro‐N, N‐dimethynaphthylamine

Lang

1977

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Triplet excited states of nitronaphthalenes. IV. 1,2‐ and 1,8‐dinitronaphthalenes

Suryanarayanan

1977

Kanosecond flash photolysis of 1,2-and 1,8-dinitronaphthalenes (1, 1, in nonpolar and polar solvents shows transient species with absorption maxima and lifetimes dependent on solvent polarity. In deaerated n-hexane the absorption maxima and lifetimes ( l / K ) are 490 nm and 1.0 psec for 1,2-L)XO& and 550 nm and 2.5 psec for l,&DNO,K. In deaerated ethanol the corresponding values are 550 nm and 4.3 psec for 1,2-DNOzN and 590 nm and 5.3 psec for l,%DNOzN. The transient absorptions are attributed to the lowest triplet excited states TI of the 1,2-and l&DNOZS. The observed red shifts in the absorption maxima of the TI states are indicative of the extent to which electronic charge is transferred intramolecularly during the 7 ' 1 + I', transitions. Furthermore, the increased lifetime of the TI states with increasing solvent polarity indicates the intramolecular charge transfer character of the Changes of dipole moments accompanying the TI -+ T,, transitions as well as rate constants for electron or proton transfer and hydrogen abstraction reactions involving the 7'1 states of 1,2-and 1,%1)N02N and tributyl tin hydride (ButSnH) as the hydrogen donor were determined together with the activation energy of the hydrogen abstraction reaction for the cme of 1,2-DNOzN. The spectroscopic and kinetic data obtained in this work demonstrate that the triplet states of 1,2-and 1,8DNOzN behave like n + T* states in nonpolar media while in polar solvents then -+ ?r* character of these states is reduced with a simultaneous increase in their intramolecular charge transfer character.states.

The triplet state of 4‐nitronaphthylamine

Lang

1977

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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.