Ultrafast excited state proton transfer dynamics of 1,2-dihydroquinolines in methanol solution

Abstract

Femtosecond and picosecond dynamics of 2,2,4,6-tetramethyl-1,2-dihydroquinoline (1) and 1,2,2,4,6-pentamethyl-1,2-dihydroquinoline (2) were studied in MeOH, MeOD, and Pr(i)OH to probe the early events of the photoinduced proton transfer (PT) between 1,2-dihydroquinolines (DHQ) and a solvent. From studies in the two solvents MeOH and Pr(i)OH and by examining the effect of deuterium replacement of proton, it has been established that PT takes 150-200 fs in MeOH, but does not occur in Pr(i)OH. The formation of PT products in the ground state proceeds concurrently to the relaxation of the higher vibrational excited singlet state to the thermally equilibrated state S(1) of DHQ. The absorption spectrum of the S(1) state was registered, and the time constant of its decay in MeOH (ca. 1 ns) agrees well with the lifetime of fluorescence measured recently by single photon counting.

Photoinduced Excited State Intramolecular Proton Transfer of New Schiff Base Derivatives with Extended Conjugated Chromophores: A Comprehensive Theoretical Survey

“…Currently, many efforts are devoted to investigating photochemical and photophysical process of ESIPT of small molecules. [8][9][10][11][12][13] As compared with small size molecules, the relative large molecular design and exhausted computation are always great challenges for chemists, the investigation of ESIPT of such molecules is extremely lower than their application potentials in various fields, and only a few studies on ESIPT of these molecules were reported. For instance, aggregationinduced ESIPT emission enhancement of some molecules was observed.…”

Femtosecond-technology-based chemical research

“…9 The photo dynamics of intermolecular proton transfer in the 1,2 dihydroquinoline-MeOH system was studied. Intermolecular proton transfer involving a non relaxed vibrationally excited state was observed experimentally.…”

Stepwise versus Concerted Mechanism of Photoinduced Proton Transfer in sec-1,2-Dihydroquinolines: Effect of Excitation Wavelength and Solvent Composition

“…29 This stepwise dynamics of the transient absorbance after the femtosecond pulse with λ pump = 350 nm crucially differs from the dynamics observed for λ pump = 308 nm, when the PT reaction was completed to the time delay of 200−500 fs. 17 It should be emphasized that, whatever the excitation wavelength is, the final product 1,2,3,4-tetrahydroquinoline is formed quantitatively, indicating that the nature of final transient species generated as a result of the PT reaction does not depend on the excitation wavelength. The results obtained set two main problems which should be considered: (i) the cause of the difference in PT dynamics at different excitation wavelengths and (ii) interpretation of the stepwise dynamics for λ pump = 350 nm.…”