Probing the excited state dynamics of a prototypical copper(I)-phenanroline complex
by
Tom Penfold(SwissFEL, Paul Scherrer Inst. (Villigen, Switzerland).)
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Description
Transition metal complexes play a central role as photocatalysts and as sensitizers in dye-sensitized solar cells and
thus understanding their photodynamic properties is of fundamental as well as practical importance. For such applications,
the Cu(I)-phenanthroline complexes are a class of systems that have recently received increasing attention [1].
These compounds exhibit many properties similar to the popular ruthenium polypyridines, but have a lower coordination
number of 4, which permits larger structural distortions in the excited state. While this offers greater flexibility to
fine tune their photophysical properties, it also gives rise to strong structure dependent energetics and susceptibility to
solvent effects [2], which has so far hampered their development.
1MLCT
hv
Ground state 3MLCT
ISC
Lifetime = 2 ns (MeCN) and 100 ns (DCM)
Here, I will present a quantum dynamics study of the prototypical copper(I)-phenanroline, [Cu(dmp)2]+ (dmp = 2,9-
dimethyl-1,10-phenanthroline), aimed at elucidating the excited state mechanisms occurring within the femtosecond
time domain. The relevant normal modes, identified by the magnitude of the first order coupling constants, correspond
closely to those observed experimentally [3]. Using the vibronic coupling Hamiltonian we construct an accurate first
principles Hamiltonian [4, 5]. The quantum dynamics, performed using the Heidelberg MCTDH package [6] yield
excited state decay components that are in agreement with those observed experimentally [7]. This allows us to clearly
resolve the mechanistic details of the ultrafast dynamics within [Cu(dmp)2]+, which have been disputed in the literature.
1. N. Armaroli, “Photoactive mono-and polynuclear Cu (I)-phenanthrolines. A viable alternative to Ru (II)-
polypyridines?,” Chem. Soc. Rev. 30, 113–124 (2001).
2. T.J. Penfold et al., “Solvent-Induced Luminescence Quenching: Static and Time-Resolved X-Ray Absorption
Spectroscopy of a Copper(I) Phenanthroline Complex,” J. Phys. Chem. A 117, 4591–4601 (2013).
3. H.Watanabe, K. Ishii, S. Takeuchi, T. Tahara, “Coherent Nuclear Dynamics in Ultrafast Photoinduced Structural
Change of Bis (diimine) copper (I) Complex,” J. Am. Chem. Soc. 133, 7728–7736 (2011).
4. G. Capano et al., “A Vibronic Coupling Hamiltonian to describe the ultrafast excited state dynamics of a Cu(I)-
phenanthroline complex,” Chimia 68, 227–230 (2014).
5. G. Capano et al., “A Quantum Dynamics Study of the Ultrafast Relaxation in a Prototypical Cu(I)-
Phenanthroline,” J. Phys. Chem. A 118, 9861–9869 (2014).
6. H.-D. Meyer, F. Gatti, and G. A.Worth, “MCTDH: Basic Theory, Extensions, and Applications to Multidimensional
Quantum Dynamics” VCH, Weinheim, Germany, (2009)
7. M. Iwamura, S. Takeuchi, T. Tahara et al., “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, 5248–5256 (2007).
