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  Absence of intramolecular charge transfer with 4-fluoro-N,N-dimethylaniline (DMA4F), contrary to an experimental report supported by computations.

Zachariasse, K. A., Demeter, A., & Druzhinin, S. I. (2017). Absence of intramolecular charge transfer with 4-fluoro-N,N-dimethylaniline (DMA4F), contrary to an experimental report supported by computations. Journal of Physical Chemistry A, 121(6), 1223-1232. doi:10.1021/acs.jpca.6b12142.

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Item Permalink: http://hdl.handle.net/11858/00-001M-0000-002D-0A52-0 Version Permalink: http://hdl.handle.net/21.11116/0000-0001-57CE-6
Genre: Journal Article

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Zachariasse, K. A., Author
Demeter, A., Author
Druzhinin, S. I.1, Author              
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1Emeritus Group of Spectroscopy and Photochemical Kinetics, MPI for Biophysical Chemistry, Max Planck Society, ou_578625              

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 Abstract: With 4-fluoro-N,N-dimethylaniline (DMA4F), only a single fluorescence from a locally excited (LE) state is observed, irrespective of solvent polarity, temperature, and excitation wavelength. The relatively small excited state dipole moment mu(e) = 7.3 D confirms the identification as LE. The single exponential fluorescence decays in the nonpolar n-hexane (2.04 ns) and in the strongly polar acetonitrile (5.73 ns) are a further support. Similar results are obtained with 4chloro-N,N-dimethylaniline (DMA4C1), having a chlorobenzene subgroup, a somewhat better electron acceptor than the fluorobenzene moiety in DMA4F. The absence of intra-molecular charge transfer (ICT) with DMA4F is in accord with its large energy gap Delta E(S-1,S-2) of 8300 cm-(1) in n-hexane between the two lowest singlet excited states, which is even larger than that (6300 cm(-1)) of N,N-dirnethylaniline (DMA), for which an LE -> ICT, reaction likewise does not occur. The results with DMA4F are in contradiction with a publication by Fujiwara et al. (Chem. Phys. Lett. 2013, 586, 70), in which the appearance of dual LE + ICT emission is reported for DMA4F in n-hexane and MeCN at room temperature. The ICT/LE fluorescence quantum yield ratio Phi/(ICT)/Phi(LE) reached a maximum value of similar to 2in- n-hexane and surprisingly also in MeCN, as the excitation wavelength approaches the red-edge of the absorption spectrum. These, in our opinion, erroneous observations were supported by time-dependent density functional theory (TDDFT) calculations, which compute a perpendicularly twisted lowest ICT state (TICT) state. This is a further example of the general tendency, of computations to find a TICT conformation for the lowest excited singlet state of electron donor/acceptor molecules such as p-substituted anilines.

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Language(s): eng - English
 Dates: 2017-01-182017-02-16
 Publication Status: Published in print
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 Rev. Method: Peer
 Identifiers: DOI: 10.1021/acs.jpca.6b12142
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Title: Journal of Physical Chemistry A
Source Genre: Journal
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Pages: - Volume / Issue: 121 (6) Sequence Number: - Start / End Page: 1223 - 1232 Identifier: -