Photophysical studies of nitronaphthalenes with electron donating substituents: dynamics and calculations
The ultrafast electronic relaxation of 4-nitronaphthylamine (NNA) in methanol and benzene solutions was studied theoretically and experi- mentally. From previous studies, it is known that the main decay process for the first singlet excited state in nitroaromatic compounds without additional substit...
| Autores: | , , |
|---|---|
| Tipo de recurso: | artículo |
| Estado: | Versión publicada |
| Fecha de publicación: | 2010 |
| País: | México |
| Institución: | Universidad Nacional Autónoma de México |
| Repositorio: | Redalyc-UNAM |
| OAI Identifier: | oai:redalyc.org:57030352012 |
| Acceso en línea: | https://www.redalyc.org/articulo.oa?id=57030352012 |
| Access Level: | acceso abierto |
| Palabra clave: | Física, Astronomía y Matemáticas nitronaphthalene nitronaphthylamine internal conversion intersystem crossing Triplet excited state |
| Sumario: | The ultrafast electronic relaxation of 4-nitronaphthylamine (NNA) in methanol and benzene solutions was studied theoretically and experi- mentally. From previous studies, it is known that the main decay process for the first singlet excited state in nitroaromatic compounds without additional substituents is intersystem crossing (ISC) between this state and a receiver triplet state with similar energy and proper electronic configuration. The results of our Time-Dependent Density Functional Theory (TD-DFT) calculations on NNA showed that the relative en- ergies between S1 and the triplet manifold are strongly solvent dependent. In particular, S1 in methanol appears at lower energies than the postulated receiver triplet state in the parent compound 1-nitronapthalene, implying that ISC may be prevented in highly polar solvents for NNA. On the other hand, the time-resolved emission measurements on NNA showed that the fluorescence is quenched in the femtosecond time- scale in both polar and non-polar solvents, indicating that the S1 lifetime is extremely short lived independent of solvent polarity. Finally, our sub-picosecond transient absorption measurements showed a totally different behavior in polar vs. non-polar solvents for NNA. The experiments revealed that the long lived first triplet state T1 of NNA is formed within a few picoseconds in benzene, while in methanol fast decaying transient signals are observed, indicating that the T1 state formation is limited by other photophysical channels. Such solvent dependence can be correlated with the significant stabilization of the S1 state in polar solvents as predicted by the TD-DFT calculations. |
|---|