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Issue 47, 2014
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Ultrafast photoinduced charge transport in Pt(II) donor–acceptor assembly bearing naphthalimide electron acceptor and phenothiazine electron donor

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Abstract

Visible light-induced charge transfer dynamics were investigated in a novel transition metal triad acceptor–chromophore–donor, (NDI–phen)Pt(II)(–C[triple bond, length as m-dash]C–Ph–CH2–PTZ)2 (1), designed for photoinduced charge separation using a combination of time-resolved infrared (TRIR) and femtosecond electronic transient absorption (TA) spectroscopy. In 1, the electron acceptor is 1,4,5,8-naphthalene diimide (NDI), and the electron donor is phenothiazine (PTZ), and [(phen)Pt(–C[triple bond, length as m-dash]C–Ph–)], where phen is 1,10-phenanthroline, represents the chromophoric core. The first excited state observed in 1 is a 3MLCT/LL′CT, with {Pt(II)–acetylide}-to-phen character. Following that, charge transfer from the phen-anion onto the NDI subunit to form NDI–phen–[Pt–(C[triple bond, length as m-dash]C)2]+–PTZ2 occurs with a time constant of 2.3 ps. This transition is characterised by appearance of the prominent NDI-anion features in both TRIR and TA spectra. The final step of the charge separation in 1 proceeds with a time constant of ∼15 ps during which the hole migrates from the [Pt–(C[triple bond, length as m-dash]C)2] subunit to one of the PTZ groups. Charge recombination in 1 then occurs with two distinct time constants of 36 ns and 107 ns, corresponding to the back electron transfer to each of the two donor groups; a rather rare occurrence which manifests that the hole in the final charge-separated state is localised on one of the two donor PTZ groups. The assignment of the nature of the excited states and dynamics in 1 was assisted by TRIR investigations of the analogous previously reported ((COOEt)2bpy)Pt(C[triple bond, length as m-dash]C–Ph–CH2–PTZ)2 (2), (J. E. McGarrah and R. Eisenberg, Inorg. Chem., 2003, 42, 4355; J. E. McGarrah, J. T. Hupp and S. N. Smirnov, J. Phys. Chem. A, 2009, 113, 6430) as well as (bpy)Pt(C[triple bond, length as m-dash]C–Ph–C7H15)2, which represent the acceptor-free dyad, and the chromophoric core, respectively. Thus, the step-wise formation of the full charge-separated state on the picosecond time scale and charge recombination via tunnelling have been established; and the presence of two distinct charge recombination pathways has been observed.

Graphical abstract: Ultrafast photoinduced charge transport in Pt(ii) donor–acceptor assembly bearing naphthalimide electron acceptor and phenothiazine electron donor

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Publication details

The article was received on 05 Sep 2014, accepted on 15 Oct 2014 and first published on 24 Oct 2014


Article type: Paper
DOI: 10.1039/C4CP03995E
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Citation: Phys. Chem. Chem. Phys., 2014,16, 25775-25788
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    Ultrafast photoinduced charge transport in Pt(II) donor–acceptor assembly bearing naphthalimide electron acceptor and phenothiazine electron donor

    I. V. Sazanovich, J. Best, P. A. Scattergood, M. Towrie, S. A. Tikhomirov, O. V. Bouganov, A. J. H. M. Meijer and J. A. Weinstein, Phys. Chem. Chem. Phys., 2014, 16, 25775
    DOI: 10.1039/C4CP03995E

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