Molecular Physics seminar

Probing the excited state dynamics of a prototypical copper(I)-phenanroline complex

by Tom Penfold (SwissFEL, Paul Scherrer Inst. (Villigen, Switzerland).)

FA31 ()


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).