title: Restricted photochemistry in the molecular solid state: structural changes on photoexcitation of Cu(I) phenanthroline metal-to-ligand charge transfer (MLCT) complexes by time-resolved diffraction.
abstract: The excited-state structure of [Cu(I)[(1,10-phenanthroline-N,N') bis(triphenylphosphine)] cations in their crystalline [BF(4)] salt has been determined at both 180 and 90 K by single-pulse time-resolved synchrotron experiments with the modified polychromatic Laue method. The two independent molecules in the crystal show distortions on MLCT excitation that differ in magnitude and direction, a difference attributed to a pronounced difference in the molecular environment of the two complexes. As the excited states differ, the decay of the emission is biexponential with two strongly different lifetimes, the longer lifetime, assigned to the more restricted molecule, becoming more prevalent as the temperature increases. Standard deviations in the current Laue study are very much lower than those achieved in a previous monochromatic study of a Cu(I) 2,9-dimethylphenanthroline substituted complex (  J. Am. Chem. Soc.     2009  ,   131  ,   6566  ), but the magnitudes of the shifts on excitation are similar, indicating that lattice restrictions dominate over the steric effect of the methyl substitution. Above all, the study illustrates emphatically that molecules in solids have physical properties different from those of isolated molecules and that their properties depend on the specific molecular environment. This conclusion is relevant for the understanding of the properties of molecular solid-state devices, which are increasingly used in current technology.
authors.affiliation: Chemistry Department, University at Buffalo, State University of New York, 14260-3000, United States.
authors.forename: Anna
authors.initials: A
authors.lastname: Makal
authors.forename: Jason
authors.initials: J
authors.lastname: Benedict
authors.forename: Elzbieta
authors.initials: E
authors.lastname: Trzop
authors.forename: Jesse
authors.initials: J
authors.lastname: Sokolow
authors.forename: Bertrand
authors.initials: B
authors.lastname: Fournier
authors.forename: Yang
authors.initials: Y
authors.lastname: Chen
authors.forename: Jarosław A
authors.initials: JA
authors.lastname: Kalinowski
authors.forename: Tim
authors.initials: T
authors.lastname: Graber
authors.forename: Robert
authors.initials: R
authors.lastname: Henning
authors.forename: Philip
authors.initials: P
authors.lastname: Coppens
mesh_terms: D003300:Copper / Q000737:chemistry*; D018360:Crystallography, X-Ray; D008024:Ligands; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D010618:Phenanthrolines / Q000737:chemistry*; D055668:Photochemical Processes; D010777:Photochemistry; D011789:Quantum Theory; D013696:Temperature; D013997:Time Factors
chemical_list: D008024:Ligands; D009942:Organometallic Compounds; D010618:Phenanthrolines; D003300:Copper