title: Ultrafast photoinduced charge transport in Pt(II) donor-acceptor assembly bearing naphthalimide electron acceptor and phenothiazine electron donor.
abstract: Visible light-induced charge transfer dynamics were investigated in a novel transition metal triad acceptor-chromophore-donor, (NDI-phen)Pt(II)(-C≡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≡C-Ph-)], where phen is 1,10-phenanthroline, represents the chromophoric core. The first excited state observed in 1 is a (3)MLCT/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≡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≡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≡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≡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.
authors.affiliation: Department of Chemistry, University of Sheffield, Sheffield, S3 7HF, UK. Julia.Weinstein@sheffield.ac.uk A.Meijer@sheffield.ac.uk.
authors.forename: Igor V
authors.initials: IV
authors.lastname: Sazanovich
authors.forename: Jonathan
authors.initials: J
authors.lastname: Best
authors.forename: Paul A
authors.initials: PA
authors.lastname: Scattergood
authors.forename: Michael
authors.initials: M
authors.lastname: Towrie
authors.forename: Sergei A
authors.initials: SA
authors.lastname: Tikhomirov
authors.forename: Oleg V
authors.initials: OV
authors.lastname: Bouganov
authors.forename: Anthony J H M
authors.initials: AJ
authors.lastname: Meijer
authors.forename: Julia A
authors.initials: JA
authors.lastname: Weinstein
mesh_terms: D004579:Electron Transport; D004583:Electrons; D008027:Light; D015394:Molecular Structure; D053644:Naphthalimides / Q000737:chemistry*; D009944:Organoplatinum Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D010640:Phenothiazines / Q000737:chemistry*; D055668:Photochemical Processes; D010984:Platinum / Q000737:chemistry*; D011789:Quantum Theory
chemical_list: D053644:Naphthalimides; D009944:Organoplatinum Compounds; D010640:Phenothiazines; D010984:Platinum; C031637:phenothiazine