Enhancing the Visible-Light Absorption and Excited-State Properties of Cu(I) MLCT Excited States

Garakyaraghi, Sofia; McCusker, Catherine E.; Khan, Saba; Koutnik, Petr; Bui, Anh Thy; Castellano, Felix N.

doi:10.1021/acs.inorgchem.7b03169

Enhancing the Visible-Light Absorption and Excited-State Properties of Cu(I) MLCT Excited States

Journal Article · Fri Feb 02 00:00:00 EST 2018 · Inorganic Chemistry

DOI:https://doi.org/10.1021/acs.inorgchem.7b03169· OSTI ID:1633632

^[1]; ^[2]; Khan, Saba ^[2]; Koutnik, Petr ^[2]; ^[2]; ^[2]

North Carolina State Univ., Raleigh, NC (United States); NC State University
North Carolina State Univ., Raleigh, NC (United States)

A computationally inspired Cu(I) metal-to-ligand charge transfer (MLCT) chromophore, [Cu(sbmpep)₂]⁺ (sbmpep = 2,9-di(sec-butyl)-3,8-dimethyl-4,7-di(phenylethynyl)-1,10-phenanthroline), was synthesized in seven total steps, prepared from either dichloro- or dibromophenanthroline precursors. Complete synthesis, structural characterization, and electrochemistry, in addition to static and dynamic photophysical properties of [Cu(sbmpep)₂]⁺, are observed on all relevant time scales. UV–Vis absorption spectroscopy revealed significant increases in oscillator strength along with a concomitant bathochromic shift in the MLCT absorption bands with respect to structurally related model complexes (ε = 16 500 M^–1 cm^–1 at 491 nm). Strong red photoluminescence (Φ = 2.7%, λ_max = 687 nm) was determined from [Cu(sbmpep)₂]⁺, which featured an average excited-state lifetime of 1.4 μs in deaerated dichloromethane. Cyclic and differential pulse voltammetry revealed ~300 mV positive shifts in the measured one-electron reversible reduction and oxidation waves in relation to a Cu(I) model complex possessing identical structural elements without the π-conjugated 4,7-substituents. The excited-state redox potential of [Cu(sbmpep)₂]⁺ was estimated to be -1.36 V, a notably powerful reductant for driving photoredox chemistry. The combination of conventional and ultrafast transient absorption and luminescence spectroscopy successfully map the excited-state dynamics of [Cu(sbmpep)₂]⁺ from initial photoexcitation to the formation of the lowest-energy MLCT excited state and ultimately its relaxation to the ground state. This newly conceived molecule appears poised for photosensitization reactions involving energy and electron-transfer processes relevant to photochemical upconversion, photoredox catalysis, and solar fuels photochemistry.

View Accepted Manuscript (DOE)

Research Organization:: North Carolina State Univ., Raleigh, NC (United States)

Sponsoring Organization:: USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Chemical Sciences, Geosciences & Biosciences Division

Grant/Contract Number:: SC0011979

OSTI ID:: 1633632

Journal Information:: Inorganic Chemistry, Journal Name: Inorganic Chemistry Journal Issue: 4 Vol. 57; ISSN 0020-1669

Publisher:: American Chemical Society (ACS)Copyright Statement

Country of Publication:: United States

Language:: English

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