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Abstract
There has been much effort to improve excited-state lifetimes in photosensitizers based on earth-abundant first-row transition metals. Copper(I) complexes have gained significant attention in this field, and in most cases, sterically-driven approaches are used to optimize their lifetimes. This study presents a series of three-coordinate copper(I) complexes (Cu1–Cu3) where the excited-state lifetime is extended by triplet-triplet energy transfer. The heteroleptic compounds feature a cyclohexyl-substituted β-diketiminate (CyNacNacMe) paired with aryl isocyanide ligands, giv-ing the general formula Cu(CyNacNacMe)(CN-Ar) (CN-dmp = 2,6-dimethylphenyl isocyanide for Cu1; CN-pyr = 1-pyrenyl isocyanide for Cu2; CN-dmp-pyr = 2,6-dimethyl-4-(1-pyrenyl)phenyl isocyanide for Cu3). The nature, energies, and dynamics of the low-energy triplet excited states are assessed with a combination of photoluminescence measurements at room temperature and 77 K, ultrafast transient absorp-tion (UFTA) spectroscopy, and DFT calculations. The complexes featuring pyrene-decorated isocyanides (Cu2 and Cu3) exhibit extended excited-state lifetimes resulting from triplet–triplet energy transfer (TTET) between the short-lived charge-transfer excited state (3CT) and the long-lived pyrene-centered triplet state (3pyr). This TTET process is irreversible in Cu3, producing exclusively the 3pyr state, and in Cu2 the 3CT and 3pyr states are nearly isoenergetic, enabling reversible TTET and long-lived 3CT luminescence. The improved photophysical proper-ties in Cu2 and Cu3 result in photocatalytic activity for stilbene E/Z isomerization via triplet energy transfer and photoredox reactivity in trans-formations involving hydrodebromination and C–O bond activation. These results illustrate that the extended excited-state lifetimes achieved through TTET resulted in newly conceived photosynthetically-relevant earth-abundant transition metal complexes.
Supplementary materials
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Supporting Information
Description
Experimental details, X-ray crystallography summary, IR spectra, UV-vis absorption spectra, excitation spectra, par-tial Kohn–Sham orbital energy-level diagrams, triplet spin density plot, decay kinetic data and lifetime, NMR spectra.
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Title
Cu1 ground state
Description
XYZ file for optimized geometry of Cu1 in the ground state, from DFT calculations
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Cu1 triplet state
Description
XYZ file for optimized geometry of Cu1 in the first triplet excited state, from DFT calculations
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Cu2 ground state
Description
XYZ file for optimized geometry of Cu2 in the ground state, from DFT calculations
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Cu2 triplet state
Description
XYZ file for optimized geometry of Cu2 in the first triplet excited state, from DFT calculations
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Cu3 ground state
Description
XYZ file for optimized geometry of Cu3 in the ground state, from DFT calculations
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Title
Cu3 triplet state
Description
XYZ file for optimized geometry of Cu3 in the first triplet excited state, from DFT calculations
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