Solar fuels catalysis is a promising route to efficiently harvesting, storing, and utilizing abundant solar energy. To achieve this promise, however, molecular systems must be designed with sustainable components that can balance numerous photophysical and chemical processes. To that end, we report on the structural and photophysical characterization of a series of Cu(I)–anthraquinone-based electron donor–acceptor dyads. The dyads utilized a heteroleptic Cu(I) bis-diimine architecture with a copper(I) bis-phenanthroline chromophore donor and anthraquinone electron acceptor. We characterized the structures of the complexes using x-ray crystallography and density functional theory calculations and the photophysical properties via resonance Raman and optical transient absorption spectroscopy. The calculations and resonance Raman spectroscopy revealed that excitation of the Cu(I) metal-to-ligand charge-transfer (MLCT) transition transfers the electron to a delocalized ligand orbital. The optical transient absorption spectroscopy demonstrated that each dyad formed the oxidized copper–reduced anthraquinone charge-separated state. Unlike most Cu(I) bis-phenanthroline complexes where increasingly bulky substituents on the phenanthroline ligands lead to longer MLCT excited-state lifetimes, here, we observe a decrease in the long-lived charge-separated state lifetime with increasing steric bulk. The charge-separated state lifetimes were best explained in the context of electron-transfer theory rather than with the energy gap law, which is typical for MLCT excited states, despite the complete conjugation between the phenanthroline and anthraquinone moieties.
REFERENCES
1.
A. J.
Morris
, G. J.
Meyer
, and E.
Fujita
, “Molecular approaches to the photocatalytic reduction of carbon dioxide for solar fuels
,” Acc. Chem. Res.
42
(12
), 1983
–1994
(2009
).2.
P. V.
Kamat
and J.
Bisquert
, “Solar fuels. Photocatalytic hydrogen generation
,” J. Phys. Chem. C
117
(29
), 14873
–14875
(2013
).3.
A.
Lavie-Cambot
, M.
Cantuel
, Y.
Leydet
, G.
Jonusauskas
, D. M.
Bassani
, and N. D.
McClenaghan
, “Improving the photophysical properties of copper(I) bis(phenanthroline) complexes
,” Coord. Chem. Rev.
252
(23–24
), 2572
–2584
(2008
).4.
M. S.
Lazorski
and F. N.
Castellano
, “Advances in the light conversion properties of Cu(I)-based photosensitizers
,” Polyhedron
82
, 57
–70
(2014
).5.
M. W.
Mara
, K. A.
Fransted
, and L. X.
Chen
, “Interplays of excited state structures and dynamics in copper(I) diimine complexes: Implications and perspectives
,” Coord. Chem. Rev.
282-283
, 2
–18
(2015
).6.
J.
Beaudelot
, S.
Oger
, S.
Peruško
, T.-A.
Phan
, T.
Teunens
, C.
Moucheron
, and G.
Evano
, “Photoactive copper complexes: Properties and applications
,” Chem. Rev.
122
(22
), 16365
–16609
(2022
).7.
Z. A.
Siddique
, Y.
Yamamoto
, T.
Ohno
, and K.
Nozaki
, “Structure-dependent photophysical properties of singlet and triplet metal-to-ligand charge transfer states in copper(I) bis(diimine) compounds
,” Inorg. Chem.
42
(20
), 6366
–6378
(2003
).8.
M. Z.
Zgierski
, “Cu(I)-2,9-dimethyl-1,10-phenanthroline: Density functional study of the structure, vibrational force-field, and excited electronic states
,” J. Chem. Phys.
118
(9
), 4045
–4051
(2003
).9.
M.
Iwamura
, S.
Takeuchi
, and T.
Tahara
, “Real-time observation of the photoinduced structural change of bis(2,9-dimethyl-1,10-phenanthroline)copper(I) by femtosecond fluorescence spectroscopy: A realistic potential curve of the Jahn–Teller distortion
,” J. Am. Chem. Soc.
129
(16
), 5248
–5256
(2007
).10.
G. B.
Shaw
, C. D.
Grant
, H.
Shirota
, E. W.
Castner
, G. J.
Meyer
, and L. X.
Chen
, “Ultrafast structural rearrangements in the MLCT excited state for copper(I) bis-phenanthrolines in solution
,” J. Am. Chem. Soc.
129
(7
), 2147
–2160
(2007
).11.
M.
Iwamura
, S.
Takeuchi
, and T.
Tahara
, “Substituent effect on the photoinduced structural change of Cu(I) complexes observed by femtosecond emission spectroscopy
,” Phys. Chem. Chem. Phys.
16
(9
), 4143
–4154
(2014
).12.
G.
Capano
, M.
Chergui
, U.
Rothlisberger
, I.
Tavernelli
, and T. J.
Penfold
, “A quantum dynamics study of the ultrafast relaxation in a prototypical Cu(I)–phenanthroline
,” J. Phys. Chem. A
118
(42
), 9861
–9869
(2014
).13.
R.
Englman
and J.
Jortner
, “The energy gap law for radiationless transitions in large molecules
,” Mol. Phys.
18
(2
), 145
–164
(1970
).14.
J. V.
Caspar
, E. M.
Kober
, B. P.
Sullivan
, and T. J.
Meyer
, “Application of the energy gap law to the decay of charge-transfer excited states
,” J. Am. Chem. Soc.
104
(2
), 630
–632
(1982
).15.
M. C.
Rosko
, E. M.
Espinoza
, S.
Arteta
, S.
Kromer
, J. P.
Wheeler
, and F. N.
Castellano
, “Employing long-range inductive effects to modulate metal-to-ligand charge transfer photoluminescence in homoleptic Cu(I) complexes
,” Inorg. Chem.
62
(7
), 3248
–3259
(2023
).16.
M. K.
Eggleston
, D. R.
McMillin
, K. S.
Koenig
, and A. J.
Pallenberg
, “Steric effects in the ground and excited states of Cu(NN)2+ systems
,” Inorg. Chem.
36
(2
), 172
–176
(1997
).17.
M.
Ruthkosky
, F. N.
Castellano
, and G. J.
Meyer
, “Photodriven electron and energy transfer from copper phenanthroline excited states
,” Inorg. Chem.
35
(22
), 6406
–6412
(1996
).18.
C. E.
McCusker
and F. N.
Castellano
, “Design of a long-lifetime, earth-abundant, aqueous compatible Cu(I) photosensitizer using cooperative steric effects
,” Inorg. Chem.
52
(14
), 8114
–8120
(2013
).19.
M.
Ruthkosky
, C. A.
Kelly
, M. C.
Zaros
, and G. J.
Meyer
, “Long-lived charge-separated states following light excitation of Cu(I) donor–acceptor compounds
,” J. Am. Chem. Soc.
119
(49
), 12004
–12005
(1997
).20.
A.
Listorti
, G.
Accorsi
, Y.
Rio
, N.
Armaroli
, O.
Moudam
, A.
Gégout
, B.
Delavaux-Nicot
, M.
Holler
, and J.-F.
Nierengarten
, “Heteroleptic copper(I) complexes coupled with methano[60]fullerene: Synthesis, electrochemistry, and photophysics
,” Inorg. Chem.
47
(14
), 6254
–6261
(2008
).21.
Y.
Rio
, G.
Enderlin
, C.
Bourgogne
, J.-F.
Nierengarten
, J.-P.
Gisselbrecht
, M.
Gross
, G.
Accorsi
, and N.
Armaroli
, “Ground and excited state electronic interactions in a bis(phenanthroline) copper(I) complex sandwiched between two fullerene subunits
,” Inorg. Chem.
42
(26
), 8783
–8793
(2003
).22.
M. S.
Lazorski
, R. H.
Gest
, and C. M.
Elliott
, “Photoinduced multistep charge separation in a heteroleptic Cu(I) bis(phenanthroline)-based donor–chromophore–acceptor triad
,” J. Am. Chem. Soc.
134
(42
), 17466
–17469
(2012
).23.
S. V.
Kirner
, D. M.
Guldi
, J. D.
Megiatto
, Jr., and D. I.
Schuster
, “Synthesis and photophysical properties of new catenated electron donor–acceptor materials with magnesium and free base porphyrins as donors and C60 as the acceptor
,” Nanoscale
7
(3
), 1145
–1160
(2015
).24.
M.
Sandroni
, Y.
Pellegrin
, and F.
Odobel
, “Heteroleptic bis-diimine copper(I) complexes for applications in solar energy conversion
,” C. R. Chim.
19
(1–2
), 79
–93
(2016
).25.
P. A.
Forero Cortés
, M.
Marx
, M.
Trose
, and M.
Beller
, “Heteroleptic copper complexes with nitrogen and phosphorus ligands in photocatalysis: Overview and perspectives
,” Chem Catal.
1
(2
), 298
–338
(2021
).26.
M.
Sandroni
, A.
Maufroy
, M.
Rebarz
, Y.
Pellegrin
, E.
Blart
, C.
Ruckebusch
, O.
Poizat
, M.
Sliwa
, and F.
Odobel
, “Design of efficient photoinduced charge separation in donor–copper(I)–acceptor triad
,” J. Phys. Chem. C
118
(49
), 28388
–28400
(2014
).27.
D.
Hayes
, L.
Kohler
, L. X.
Chen
, and K. L.
Mulfort
, “Ligand mediation of vectorial charge transfer in Cu(I)diimine chromophore–acceptor dyads
,” J. Phys. Chem. Lett.
9
(8
), 2070
–2076
(2018
).28.
D.
Hayes
, L.
Kohler
, R. G.
Hadt
, X.
Zhang
, C.
Liu
, K. L.
Mulfort
, and L. X.
Chen
, “Excited state electron and energy relays in supramolecular dinuclear complexes revealed by ultrafast optical and X-ray transient absorption spectroscopy
,” Chem. Sci.
9
(4
), 860
–875
(2018
).29.
Z.
Singh
, S.
Kamal
, and M. B.
Majewski
, “Copper(I) donor–chromophore–acceptor assembly for light-driven oxidation on a zinc oxide nanowire electrode
,” J. Phys. Chem. C
126
(39
), 16732
–16743
(2022
).30.
L.
Wang
, Z.-L.
Xie
, B. T.
Phelan
, V. M.
Lynch
, L. X.
Chen
, and K. L.
Mulfort
, “Changing directions: Influence of ligand electronics on the directionality and kinetics of photoinduced charge transfer in Cu(I)diimine complexes
,” Inorg. Chem.
62
(35
), 14368
–14376
(2023
).31.
B.
Rosa López
, L.
Bárbara Loeb
, T.
Boussie
, and T. J.
Meyer
, “Synthesis of a new phenanthroline derived ligand with acceptor properties
,” Tetrahedron Lett.
37
(31
), 5437
–5440
(1996
).32.
Z.-L.
Xie
, N.
Gupta
, J.
Niklas
, O. G.
Poluektov
, V. M.
Lynch
, K. D.
Glusac
, and K. L.
Mulfort
, “Photochemical charge accumulation in a heteroleptic copper(I)-anthraquinone molecular dyad via proton-coupled electron transfer
,” Chem. Sci.
14
(37
), 10219
–10235
(2023
).33.
M.
Schmittel
and A.
Ganz
, “Stable mixed phenanthroline copper(I) complexes. Key building blocks for supramolecular coordination chemistry
,” Chem. Commun.
1997
(11
), 999
–1000
.34.
M.
Schmittel
, C.
Michel
, S.-X.
Liu
, D.
Schildbach
, and D.
Fenske
, “New sterically encumbered 2,9-diarylphenanthrolines for the selective formation of heteroleptic bis(phenanthroline)copper(I) complexes
,” Eur. J. Inorg. Chem.
2001
(5
), 1155
–1166
().35.
S.
De
, K.
Mahata
, and M.
Schmittel
, “Metal-coordination-driven dynamic heteroleptic architectures
,” Chem. Soc. Rev.
39
(5
), 1555
–1575
(2010
).36.
L.
Yang
, D. R.
Powell
, and R. P.
Houser
, “Structural variation in copper(I) complexes with pyridylmethylamide ligands: Structural analysis with a new four-coordinate geometry index, τ4
,” Dalton Trans.
2007
(9
), 955
–964
.37.
L.
Kohler
, D.
Hayes
, J.
Hong
, T. J.
Carter
, M. L.
Shelby
, K. A.
Fransted
, L. X.
Chen
, and K. L.
Mulfort
, “Synthesis, structure, ultrafast kinetics, and light-induced dynamics of CuHETPHEN chromophores
,” Dalton Trans.
45
(24
), 9871
–9883
(2016
).38.
J.-D.
Chai
and M.
Head-Gordon
, “Long-range corrected hybrid density functionals with damped atom–atom dispersion corrections
,” Phys. Chem. Chem. Phys.
10
(44
), 6615
–6620
(2008
).39.
M. W.
Mara
, B. T.
Phelan
, Z.-L.
Xie
, T. W.
Kim
, D. J.
Hsu
, X.
Liu
, A. J. S.
Valentine
, P.
Kim
, X.
Li
, S.-i.
Adachi
et al, “Unveiling ultrafast dynamics in bridged bimetallic complexes using optical and X-ray transient absorption spectroscopies
,” Chem. Sci.
13
(6
), 1715
–1724
(2022
).40.
R. L.
Martin
, “Natural transition orbitals
,” J. Chem. Phys.
118
(11
), 4775
–4777
(2003
).41.
R.
López
, A. M.
Leiva
, F.
Zuloaga
, B.
Loeb
, E.
Norambuena
, K. M.
Omberg
, J. R.
Schoonover
, D.
Striplin
, M.
Devenney
, and T. J.
Meyer
, “Excited-state electron transfer in a chromophore–quencher complex. Spectroscopic identification of a redox-separated state
,” Inorg. Chem.
38
(12
), 2924
–2930
(1999
).42.
M.
Iwamura
, S.
Takeuchi
, and T.
Tahara
, “Ultrafast excited-state dynamics of copper(I) complexes
,” Acc. Chem. Res.
48
(3
), 782
–791
(2015
).43.
N. A.
Gothard
, M. W.
Mara
, J.
Huang
, J. M.
Szarko
, B.
Rolczynski
, J. V.
Lockard
, and L. X.
Chen
, “Strong steric hindrance effect on excited state structural dynamics of Cu(I) diimine complexes
,” J. Phys. Chem. A
116
(9
), 1984
–1992
(2012
).44.
M. W.
Mara
, N. E.
Jackson
, J.
Huang
, A. B.
Stickrath
, X.
Zhang
, N. A.
Gothard
, M. A.
Ratner
, and L. X.
Chen
, “Effects of electronic and nuclear interactions on the excited-state properties and structural dynamics of copper(I) diimine complexes
,” J. Phys. Chem. B
117
(6
), 1921
–1931
(2013
).45.
A. P.
Scott
and L.
Radom
, “Harmonic vibrational frequencies: An evaluation of Hartree–Fock, Møller–Plesset, quadratic configuration interaction, density functional theory, and semiempirical scale factors
,” J. Phys. Chem.
100
(41
), 16502
–16513
(1996
).46.
M. D.
Halls
, J.
Velkovski
, and H. B.
Schlegel
, “Harmonic frequency scaling factors for Hartree-Fock, S-VWN, B-LYP, B3-LYP, B3-PW91 and MP2 with the Sadlej pVTZ electric property basis set
,” Theor. Chem. Acc.
105
(6
), 413
–421
(2001
).47.
J. P.
Merrick
, D.
Moran
, and L.
Radom
, “An evaluation of harmonic vibrational frequency scale factors
,” J. Phys. Chem. A
111
(45
), 11683
–11700
(2007
).48.
B. S.
Brunschwig
, S.
Ehrenson
, and N.
Sutin
, “Solvent reorganization in optical and thermal electron-transfer processes
,” J. Phys. Chem.
90
(16
), 3657
–3668
(1986
).49.
R. A.
Marcus
, “On the theory of oxidation-reduction reactions involving electron transfer. I
,” J. Chem. Phys.
24
(5
), 966
–978
(1956
).50.
A. B.
Myers
, “Resonance Raman intensities and charge-transfer reorganization energies
,” Chem. Rev.
96
(3
), 911
–926
(1996
).51.
J. L.
McHale
, “Subpicosecond solvent dynamics in charge-transfer transitions: Challenges and opportunities in resonance Raman spectroscopy
,” Acc. Chem. Res.
34
(4
), 265
–272
(2001
).52.
M.
Wächtler
, J.
Guthmuller
, S.
Kupfer
, M.
Maiuri
, D.
Brida
, J.
Popp
, S.
Rau
, G.
Cerullo
, and B.
Dietzek
, “Ultrafast intramolecular relaxation and wave-packet motion in a ruthenium-based supramolecular photocatalyst
,” Chem. - Eur. J.
21
(21
), 7668
–7674
(2015
).53.
M.
Iwamura
, H.
Watanabe
, K.
Ishii
, S.
Takeuchi
, and T.
Tahara
, “Coherent nuclear dynamics in ultrafast photoinduced structural change of bis(diimine)copper(I) complex
,” J. Am. Chem. Soc.
133
(20
), 7728
–7736
(2011
).54.
L.
Hua
, M.
Iwamura
, S.
Takeuchi
, and T.
Tahara
, “The substituent effect on the MLCT excited state dynamics of Cu(I) complexes studied by femtosecond time-resolved absorption and observation of coherent nuclear wavepacket motion
,” Phys. Chem. Chem. Phys.
17
(3
), 2067
–2077
(2015
).55.
S.
Garakyaraghi
, E. O.
Danilov
, C. E.
McCusker
, and F. N.
Castellano
, “Transient absorption dynamics of sterically congested Cu(I) MLCT excited states
,” J. Phys. Chem. A
119
(13
), 3181
–3193
(2015
).56.
A.
Guda
, J.
Windisch
, B.
Probst
, J. A.
van Bokhoven
, R.
Alberto
, M.
Nachtegaal
, L. X.
Chen
, and G.
Smolentsev
, “Excited-state structure of copper phenanthroline-based photosensitizers
,” Phys. Chem. Chem. Phys.
23
(47
), 26729
–26736
(2021
).57.
J.
Cody
, J.
Dennisson
, J.
Gilmore
, D. G.
VanDerveer
, M. M.
Henary
, A.
Gabrielli
, C. D.
Sherrill
, Y.
Zhang
, C.-P.
Pan
, C.
Burda
, and C. J.
Fahrni
, “X-ray structures, photophysical characterization, and computational analysis of geometrically constrained copper(I)–phenanthroline complexes
,” Inorg. Chem.
42
(16
), 4918
–4929
(2003
).58.
A. C. S.
Samia
, J.
Cody
, C. J.
Fahrni
, and C.
Burda
, “The effect of ligand constraints on the metal-to-ligand charge-tranfer relaxation dynamics of copper(I)–phenanthroline complexes: A comparative study by femtosecond time-resolved spectroscopy
,” J. Phys. Chem. B
108
(2
), 563
–569
(2004
).59.
R. A.
Marcus
and N.
Sutin
, “Electron transfers in chemistry and biology
,” Biochim. Biophys. Acta, Rev. Bioenerg.
811
(3
), 265
–322
(1985
).60.
R. A.
Marcus
and N.
Sutin
, “The relation between the barriers for thermal and optical electron transfer reactions in solution
,” Comments Inorg. Chem.
5
(3
), 119
–133
(1986
).61.
J. R.
Bolton
and M. D.
Archer
, “Basic electron-transfer theory
,” in Electron Transfer in Inorganic, Organic, and Biological Systems
, Advances in Chemistry Vol. 228
(American Chemical Society
, 1991
), pp. 7
–23
.© 2024 Author(s). Published under an exclusive license by AIP Publishing.
2024
Author(s)
You do not currently have access to this content.
