Electron transfer dynamics and excited state branching in a charge-transfer platinum(ii) donor-bridge-acceptor assembly

Paul A. Scattergood, Milan Delor, Igor V. Sazanovich, Oleg V. Bouganov, Sergei A. Tikhomirov, Alexander S. Stasheuski, Anthony W. Parker, Gregory M. Greetham, Michael Towrie, E. Stephen Davies, Anthony J H M Meijer, Julia A. Weinstein

Research output: Contribution to journalArticle

26 Citations (Scopus)

Abstract

A linear asymmetric Pt(ii) trans-acetylide donor-bridge-acceptor triad designed for efficient charge separation, NAPPt(PBu3)2Ph-CH2-PTZ (1), containing strong electron acceptor and donor groups, 4-ethynyl-N-octyl-1,8-naphthalimide (NAP) and phenothiazine (PTZ) respectively, has been synthesised and its photoinduced charge transfer processes characterised in detail. Excitation with 400 nm, ∼50 fs laser pulse initially populates a charge transfer manifold stemming from electron transfer from the Pt-acetylide centre to the NAP acceptor and triggers a cascade of charge and energy transfer events. A combination of ultrafast time-resolved infrared (TRIR) and transient absorption (TA) spectroscopies, supported by UV-Vis/IR spectroelectrochemistry, emission spectroscopy and DFT calculations reveals a self-consistent photophysical picture of the excited state evolution from femto- to milliseconds. The characteristic features of the NAP-anion and PTZ-cation are clearly observed in both the TRIR and TA spectra, confirming the occurrence of electron transfer and allowing the rate constants of individual ET-steps to be obtained. Intriguingly, 1 has three separate ultrafast electron transfer pathways from a non-thermalised charge transfer manifold directly observed by TRIR on timescales ranging from 0.2 to 14 ps: charge recombination to form either the intraligand triplet 3NAP with 57% yield, or the ground state, and forward electron transfer to form the full charge-separated state 3CSS (3[PTZ+-NAP-]) with 10% yield as determined by target analysis. The 3CSS decays by charge-recombination to the ground state with ∼1 ns lifetime. The lowest excited state is 3NAP, which possesses a long lifetime of 190 μs and efficiently sensitises singlet oxygen. Overall, molecular donor-bridge-acceptor triad 1 demonstrates excited state branching over 3 different pathways, including formation of a long-distant (18 Å) full charge-separated excited state from a directly observed vibrationally hot precursor state.

Original languageEnglish
Pages (from-to)17677-17693
Number of pages17
JournalDalton Transactions
Volume43
Issue number47
Early online date31 Oct 2014
DOIs
Publication statusPublished - 21 Dec 2014
Externally publishedYes

Fingerprint Dive into the research topics of 'Electron transfer dynamics and excited state branching in a charge-transfer platinum(ii) donor-bridge-acceptor assembly'. Together they form a unique fingerprint.

  • Cite this

    Scattergood, P. A., Delor, M., Sazanovich, I. V., Bouganov, O. V., Tikhomirov, S. A., Stasheuski, A. S., Parker, A. W., Greetham, G. M., Towrie, M., Davies, E. S., Meijer, A. J. H. M., & Weinstein, J. A. (2014). Electron transfer dynamics and excited state branching in a charge-transfer platinum(ii) donor-bridge-acceptor assembly. Dalton Transactions, 43(47), 17677-17693. https://doi.org/10.1039/c4dt01682c