Probing the Electronic Structure of a Photoexcited Solar Cell Dye with Transient X-ray Absorption Spectroscopy

Benjamin E Van Kuiken; Nils Huse; Hana Cho; Matthew L Strader; Michael S Lynch; Robert W Schoenlein; Munira Khalil

doi:10.1021/jz300671e

Probing the Electronic Structure of a Photoexcited Solar Cell Dye with Transient X-ray Absorption Spectroscopy

J Phys Chem Lett. 2012 Jun 21;3(12):1695-700. doi: 10.1021/jz300671e. Epub 2012 Jun 8.

Authors

Benjamin E Van Kuiken¹, Nils Huse², Hana Cho², Matthew L Strader², Michael S Lynch¹, Robert W Schoenlein², Munira Khalil¹

Affiliations

¹ †Department of Chemistry, University of Washington, Seattle, Washington 98195, United States.
² ‡Ultrafast X-ray Science Laboratory, Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.

PMID: 26285730
DOI: 10.1021/jz300671e

Abstract

This study uses transient X-ray absorption (XA) spectroscopy and time-dependent density functional theory (TD-DFT) to directly visualize the charge density around the metal atom and the surrounding ligands following an ultrafast metal-to-ligand charge-transfer (MLCT) process in the widely used Ru(II) solar cell dye, Ru(dcbpy)2(NCS)2 (termed N3). We measure the Ru L-edge XA spectra of the singlet ground ((1)A1) and the transient triplet ((3)MLCT) excited state of N3(4-) and perform TD-DFT calculations of 2p core-level excitations, which identify a unique spectral signature of the electron density on the NCS ligands. We find that the Ru 2p, Ru eg, and NCS π* orbitals are stabilized by 2.0, 1.0, and 0.6 eV, respectively, in the transient (3)MLCT state of the dye. These results highlight the role of the NCS ligands in governing the oxidation state of the Ru center.

Keywords: charge transfer; core-level excitation; excited states; transient X-ray absorption.