Picosecond reversible reaction kinetics of excited p-dimethylaminoacetophenone and m-methyl-p-cyanodimethylaniline studied by oxygen quenching technique
An improved model of a ckputer-controlled picosecond absorption spectrometer was designed and constructed. Its operatioii is described, and applied to the measurement of transient spectra of p-N, N-dioctylamino--acetophenone. The spectroscopy and photophysics of this ckpound are ckpared to the other ckpounds exhibiting the dual fluorescence, assigned usually to the adiabatic formation of the "twisted" intramolecular charge transfer excited state. The data are discussed in relatioii to alternative suggestion of an inversioii of the pyramidal amino nitrogen atk. The whole evidence supports the decoupling of the π-electronic systems of D+ and A-in the D+-A -polar excited state, in full accord with the "twisted" intramolecular charge transfer model. The peculiar behaviour of the long alkyl -NR2 derivatives (favouring the "twisted" intramolecular charge transfer state emission) seems to be primarily due to the decreasing oxidation potential of such electron donor groups.
An improved model of a ckputer-controlled picosecond absorption spectrometer was designed and constructed. Its operatioii is described, and applied to the measurement of transient spectra of p-N, N-dioctylamino--acetophenone. The spectroscopy and photophysics of this ckpound are ckpared to the other ckpounds exhibiting the dual fluorescence, assigned usually to the adiabatic formation of the "twisted" intramolecular charge transfer excited state. The data are discussed in relatioii to alternative suggestion of an inversioii of the pyramidal amino nitrogen atk. The whole evidence supports the decoupling of the π-electronic systems of D+ and A-in the D+-A -polar excited state, in full accord with the "twisted" intramolecular charge transfer model. The peculiar behaviour of the long alkyl -NR2 derivatives (favouring the "twisted" intramolecular charge transfer state emission) seems to be primarily due to the decreasing oxidation potential of such electron donor groups.
“…The effect of varying acceptor strength on the energetics of the excited states involved will be discussed in more detail below in combination with the applicability of the multiple state model to 1-Cl 1-OMe , 2-Cl , and 2-OMe . 3 Chemical Structures of the Related Benzoxazinone, D−A−Stilbene, and Benzofuran 61 Derivatives, Michler's Ketone, DMABK, and DMABI 64 …”
From the fluorescence properties of chalcones as a function of solvent polarity, and by the comparison to
derivatives with donors and acceptors and with various selectively bridged bonds, it can be concluded that
two emissive and two nonemissive states are needed to describe the fluorescence behavior. Three of these
states are connected with bond twisting and lead to species with high or low dipole moment, two of them
situated in the proximity of a conical intersection.
“…S o transition is expected to be strongly forbidden. 8 For instance, the TICT state k f value for a close analogue of DMABN, 2-methyl-DMABN is, in polar solvents, within the limits of (0.4-1.5 Â 10 7 s À1 ), 43,44 whereas in the case of Py-BN in polar solvents the value of the radiative rate constant is about one order of magnitude higher (see Table 1).…”
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