A stronger acceptor decreases the rates of charge transfer: Ultrafast dynamics and on/off switching of charge separation in organometallic donor-bridge-acceptor systems

Alexander Auty, Paul Scattergood, Theo Keane, Tao Cheng, Guanzhi Wu, Heather Carson, James Shipp, Andrew Sadler, Thomas M. Roseveare, Igor V. Sazanovich, Anthony J H M Meijer, Dimitri Chekulaev, Paul Elliott, Michael Towrie, Julia A. Weinstein

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2 Citations (Scopus)


To unravel the role of driving force and structural changes in directing the photoinduced pathways in donor-bridge-acceptor (DBA) systems, we compared the ultrafast dynamics in novel DBAs which share a phenothiazine (PTZ) electron donor and a Pt(ii) trans-acetylide bridge (-C = C-Pt-C C-), but bear different acceptors conjugated into the bridge (naphthalene-diimide, NDI; or naphthalene-monoimide, NAP). The excited state dynamics were elucidated by transient absorption, time-resolved infrared (TRIR, directly following electron density changes on the bridge/acceptor), and broadband fluorescence-upconversion (FLUP, directly following sub-picosecond intersystem crossing) spectroscopies, supported by TDDFT calculations. Direct conjugation of a strong acceptor into the bridge leads to switching of the lowest excited state from the intraligand 3IL state to the desired charge-separated 3CSS state. We observe two surprising effects of an increased strength of the acceptor in NDI vs. NAP: a ca. 70-fold slow-down of the 3CSS formation—(971 ps) −1vs. (14 ps) −1, and a longer lifetime of the 3CSS (5.9 vs. 1 ns); these are attributed to differences in the driving force ΔG et, and to distance dependence. The 100-fold increase in the rate of intersystem crossing—to sub-500 fs—by the stronger acceptor highlights the role of delocalisation across the heavy-atom containing bridge in this process. The close proximity of several excited states allows one to control the yield of 3CSS from ∼100% to 0% by solvent polarity. The new DBAs offer a versatile platform for investigating the role of bridge vibrations as a tool to control excited state dynamics.

Original languageEnglish
Pages (from-to)11417-11428
Number of pages12
JournalChemical Science
Issue number41
Early online date28 Sep 2023
Publication statusPublished - 7 Nov 2023

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