Nature and Dynamics of the Excited States of Ethynyl-Functionalized Naphthalimide-Phenanthroline Re(I) Complexes Studied by TA and TRIR Spectroscopies.

The synthesis and photophysical properties of four [Re(R-NI-phen)(CO)Cl] complexes (), where NI = 1,8-naphthalimide and phen = 1,10-phenanthroline, are reported. The R-NI chromophores were substituted at their 4-positions with R = H (), ethynyl benzene (), ethynyl thiophene (), ethynyl trimethylsilane (), yielding a series of metal-organic bichromophores. The organic chromophores were investigated in parallel to better understand the photophysical properties exhibited in the complexes. The excited-state processes of these molecules were studied by transient absorption and time-resolved infrared spectroscopies, to unravel the kinetics of the energy transfer processes occurring in the series. Namely, the interplay between the singlet ligand-centered (LC), the triplet metal-to-ligand charge-transfer (MLCT), and the triplet ligand-centered (LC) excited states were studied using these time-resolved spectroscopic techniques, supported by quantum chemical calculations, to monitor the changing excited-state dynamics in the series. These studies reveal that the thermal equilibrium between the MLCT and LC excited states present in is modulated in favor of the LC excited state in the remaining series, giving rise to increasingly ligand-like photophysics as the electron-donating strength of the R-group increases.