Probing the excited state dynamics of a new family of Cu(I)-complexes with an enhanced light absorption capacity: excitation-wavelength dependent population of states through branching

The ultrafast dynamics of six homoleptic Cu(I)-complexes and their respective ligands was examined through time-resolved electronic absorption spectroscopy in the subpicosecond time domain, in a variety of solvents, and at different excitation wavelengths. Results indicate that after excitation of the complexes in the blue part of the spectrum, the initially formed intraligand (IL) singlet excited state decays via two pathways yielding simultaneously both the lower-lying MLCT excited state and the ligand locally excited triplet state. The latter is also observed in the case of the free ligands and relaxes back to the ground state in a timescale of 40 ps. Excitation in the red part results in the formation of the MLCT excited state of the complexes which decays to the ground state through the same intraligand triplet excited state. The solvent viscosity does not affect the overall relaxation kinetics. The short time constant observed for the intersystem crossing of the MLCT singlet excited state is discussed in terms of the contribution of the d-orbitals of copper to the wavefunction of these states.