Excited-state relaxation dynamics of Re(I) tricarbonyl complexes with macrocyclic phenanthroline ligands studied by time-resolved IR spectroscopy.
Two sets of supramolecular rhenium carbonyl-phenanthroline complexes were prepared: fac-[Re(Cl)(CO)(3)(N,N)] and fac-[Re(Etpy)(CO)(3)(N,N)](+), where N,N is 2,9-di-anisyl-1,10-phenanthroline (dap) or two related macrocyclic ligands, where the two anisyl groups are connected by a polyether chain of different length and rigidity (m27, m30), which wraps around and above the equatorial Re(CO)(2) group. The excited-state character and relaxation dynamics of these complexes were investigated by picosecond time-resolved IR spectroscopy in the spectral region of C[triple bond, length as m-dash]O stretching vibrations, nu(CO). The results were interpreted with the aid of DFT and TD-DFT calculations of the molecular structures and electron-density redistribution upon excitation. [Re(Cl)(CO)(3)(phen-macrocycle)] in CH(2)Cl(2) have the same type of lowest excited state as analogous acyclic phen or bpy complexes, that is a mixed Re(CO)(3)-->phen and Cl-->phen MLCT/XLCT, together with some pipi*(phen) IL character. Its relaxation dynamics are qualitatively similar to those of phen or bpy complexes. However, relaxation of [Re(Cl)(CO)(3)(m30)] shows a slow kinetics component ( approximately 22 ps) which arises from confined local solvent molecules and/or from conformational movements of the flexible m30 polyether ring. In contrast, attaching anisyl groups at the 2 and 9 phen positions in [Re(Etpy)(CO)(3)(phen-macrocycle)](+) effectively "freezes" excited-state relaxation in MeCN, regardless of the presence of the macrocyclic ring. The lowest excited triplet state has a mixed MLCT/IL character. Restricting the solvent access to the excited chromophore clearly affects both the character and dynamics of the lowest excited state.
School of Biological and Chemical Sciences, Queen Mary, University of London, Mile End Road, London, United KingdomE1 4NS.
Ana María
AM
Blanco-Rodríguez
Michael
M
Towrie
Jean-Paul
JP
Collin
Stanislav
S
Zális
Antonín
A
Vlcek
D008024:Ligands; D047028:Macrocyclic Compounds / Q000737:chemistry*; D015394:Molecular Structure; D010618:Phenanthrolines / Q000737:chemistry*; D011789:Quantum Theory; D012211:Rhenium / Q000737:chemistry*; D013055:Spectrophotometry, Infrared
D008024:Ligands; D047028:Macrocyclic Compounds; D010618:Phenanthrolines; D012211:Rhenium