Flash photolysis and quenching studies of copper(I) systems in the presence of Lewis bases: inorganic exciplexes?

Abstract

Picosecond flash photolysis studies of Cu(dmp)2+ and Cu(bcp)2+ have been carried out, where dmp denotes 2,9-dimethyl-1,10phenanthroline and bcp is 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline. In each case the excited-state absorption spectrum resembles that of the radical anion of 1,10-phenanthroline, consistent with the charge-transfer nature of the excited state. With this technique we have for the first time been able to measure the excited-state lifetime (2 ± 0.3 ns at 20 °C) of Cu(dmp)2+ in acetonitrile. The quenching kinetics of photoexcited Cu(dmp)2+ by acetonitrile, acetone, and p-dioxane in CH2C12 solution have been determined from studies of the luminescence lifetime, and the results are interpreted in terms of a mechanism in which deactivation follows the formation of a complex denoted as *Cu-Q. The fact that AH* is negative for all three quenchers suggests that *Cu-Q may represent an exciplex in which the quencher (Lewis base) serves as a fifth donor for the copper center. Exciplex emission has not been detected; however, the kinetic data indicate that the steady-state concentration of *Cu-Q is quite small. Whether the five-coordinate adduct represents a kinetic intermediate, a successor complex, or even the transition state of the reaction cannot be determined rigorously from our data, but bond formation has been shown to be an essential part of the quenching process. Finally, we consider reasons why exciplexes are not commonly observed for the excited states of transition-metal complexes.

Ultrafast Structural Rearrangements in the MLCT Excited State for Copper(I) bis-Phenanthrolines in Solution

“…Copper(I) diimine coordination complexes (denoted [Cu I (NN) 2 ] + ) have a long, rich history that parallels that of their transition-metal cousins, polypyridyl ruthenium(II) systems [1][2][3][4][5][6][7][8][9][10][11] . Current interest is driven by a desire to employ transition metal coordination complexes in applications from solar energy conversion 12 to chemical sensing 13,14 and molecular devices.…”

“…18 McMillin and coworkers 3,[19][20][21][22][23][24] performed pioneering work for elucidating the unique photophysics and photochemistry of [Cu I (NN) 2 ] + complexes and developed a fundamental picture of the photophysics occurring on the nanosecond timescale. 6 Their experimental observations led to remarkable insights into the properties of these systems in their excited states. McMillin recognized the potential for JahnTeller distortion causing a structural rearrangement from the tetrahedral ground state to square planar or trigonal bipyramidal geometries following a metal-to-ligand-charge-transfer (MLCT) excitation in [Cu I (NN) 2 ] + complexes.…”

Switching‐on: The Copper Age

“…In this excited-state with flattened tetrahedral geometry, an additional axial coordination site is exposed for nucleophilic attack (by solvent, counteranion or other Lewis bases present in solution) generating a ''pentacoordinated exciplex'' (see Figure 13.1). In the last decade, much effort has been made to elucidate these processes using a wide range of techniques to aid in understanding and exploiting their potential [60,[90][91][92][93][94][95][96][97][98][99][100][101][102][103][104][105][106][107].…”

Momentaufnahmen photoangeregter Moleküle in fehlgeordneten Medien mit gepulster Synchrotron‐Röntgenstrahlung

“…Im EA-Spektralbereich wird 10-20 ps nach der Anregung die charakteristische Doppelbande des dmpC À -Ions [139,144] nachgewiesen, die durch Blauverschiebung und spektrale Verengung der energieärmeren Seite der Absorptionsbande bei 570-600 nm entsteht. Mit Zeitkonstanten von 1.7 ns für Acetonitril-und 100 ns für Toluollösungen nimmt dann die Intensität der gesamten Bande ab.…”