RESUMO
The dynamics of a substituted proton sponge-the 1,8-bis(dimethylamino)-4-cyanonaphthalene (DMAN-CN) molecule-was investigated after excitation in the S1 state. Experimental and theoretical information are reported. The former includes absorption, fluorescence, and time-resolved transient absorption spectra, which were recorded in solution. Real-time dynamics measurements were also performed on gas-phase isolated DMAN-CN. TD DFT/6-31G(d,p) level and CIS/6-31G(d,p) excited-state calculations complement these results. This has allowed revisiting the energy transfer process between a locally excited (LE) and a charge transfer (CT) state, which is often invoked with this kind of molecule.
RESUMO
The results of the steady-state and time-resolved fluorescence-spectroscopy measurements and DFT calculations for trans-[4-(4'-dimethylaminostyryl)] pyridine N-oxide (trans-DPO) in various solvents are presented. These results are similar to those reported in the literature for trans-4-(dimethylamino)-4'-cyanostilbene (DCS) where the S1 emissive state shows the charge-transfer (CT) nature. Alcohol solvents, however, have aroused our particular interest because hydrogen-bonded complexes are formed between them and the trans-DPO molecule. They demonstrate a stronger CT character of the lower lying excited state and a larger separation between the first and the second absorption band than in the free trans-DPO molecule. The different effects found in time-dependent femtosecond up-conversion (performed for several emission wavelengths in dioxane and methanol solution over the time range 0-40 ps) were assigned to the hydrogen bond assisted charge transfer process in trans-DPO in methanol, to the excited-state solvation dynamics and mainly to solvent relaxation of trans-DPO dissolved in dioxane and methanol.
