Excited state molecular structure determination in disordered media using laser pump/x-ray probe time-domain x-ray absorption spectroscopy.
Advances in X-ray technologies provide opportunities for solving structures of photoexcited state molecules with short lifetimes. Using X-ray pulses from a modern synchrotron source, the structure of a metal-to-ligand-charge-transfer (MLCT) excited state of CuI(dmp)2+ (dmp 1/4 2,9-dimethyl-1,10-phenanthroline) was investigated by laser pump/X-ray probe X-ray absorption fine structure (LPXP-XAFS) in fluid solution at room temperature on a nanosecond time scale. The experimental requirements for such pump-probe XAFS are described in terms of technical challenges: (1) conversion of optimal excited state population, (2) synchronization of the pump laser pulse and probe Xray pulse, and (3) timing of the detection. Using a laser pump pulse for the photoexcitation, a photoluminescent MLCT excited state of CuI(dmp)2(BArF), (dmp 1/4 2,9-dimethyl-1,10-phenanthroline), BArF 1/4 tetrakis(3,5-bis(trifluoromethylphenyl)borate) with a lifetime of 98{+-}5 ns was created. Probing the structure of this state at its optimal concentration using an X-ray pulse cluster with a total duration of 14.2 ns revealed that (1) a Cu{sup II} center was generated via a whole charge transfer; (2) the copper in the MLCT state bound an additional ligand to form a penta-coordinate complex with a likely trigonal bipyramidal geometry; and (3) the average Cu-N bond length increases in the MLCT excited state by 0.07 . In contrast to previously reported literature, the photoluminescence of this pentacoordinate MLCT state was not quenched upon ligation with the fifth ligand. On the basis of experimental results, we propose that the absorptive and emissive states have distinct geometries. The results represent X-ray characterization of a molecular excited state in fluid solution on a nanosecond time scale.
- Research Organization:
- Argonne National Laboratory (ANL)
- Sponsoring Organization:
- SC
- DOE Contract Number:
- AC02-06CH11357
- OSTI ID:
- 949621
- Report Number(s):
- ANL/CHM/JA-42604
- Journal Information:
- Faraday Discuss., Journal Name: Faraday Discuss. Journal Issue: 2003 Vol. 122; ISSN 1359-6640
- Country of Publication:
- United States
- Language:
- ENGLISH
Similar Records
Rapid excited state structural reorganization captured by pulsed x-rays.
Capturing excited state molecular structures in disordered media with 100-ps time resolution by laser pump x-ray probe XAFS.
MLCT state structure and dynamics of a copper(I) diimine complex characterized by pump-probe x-ray and laser spectroscopies and DFT calculations.
Journal Article
·
Wed Sep 11 00:00:00 EDT 2002
· J. Am. Chem. Soc.
·
OSTI ID:949431
Capturing excited state molecular structures in disordered media with 100-ps time resolution by laser pump x-ray probe XAFS.
Conference
·
Fri Dec 31 23:00:00 EST 2004
· Phys. Scr.
·
OSTI ID:991600
MLCT state structure and dynamics of a copper(I) diimine complex characterized by pump-probe x-ray and laser spectroscopies and DFT calculations.
Journal Article
·
Wed Jun 11 00:00:00 EDT 2003
· J. Am. Chem. Soc.
·
OSTI ID:961151