Photochemistry of (η³-allyl)Ru(CO)₃X Precursors for Photoassisted Chemical Vapor Deposition

Abstract

Quantum yields for loss of a single CO ligand in alkane solutions were determined for the (η3-allyl)­Ru­(CO)3X complexes, where X = Cl, Br, I. The three complexes had similar quantum yields at λexc = 254 nm, while the quantum yields obtained at 313 nm followed a trend of ΦBr > ΦCl > ΦI. A wavelength dependence of the quantum yields in the order Φ254 < Φ313 < Φ334 was observed for the iodo complex. Very low levels of luminescence were observed for the compounds, demonstrating that radiative decay of the excited states was not competitive with nonradiative processes, including photochemical reactions. Excited states were assigned as MLCT or LF on the basis of solvatochromism and DFT studies.

Photochemistry of (η4-diene)Ru(CO)3Complexes as Precursor Candidates for Photoassisted Chemical Vapor Deposition

“…A higher energy transition was classified as MLCT from metal d to olefin π*. These results are consistent with the photochemistry at the lowest-energy excitation band most likely occurring from an LF transition, which is in agreement with previously reported data on photosubstitution. , Although CO dissociation after population of the CO π* orbital of (η 3 -allyl)­Ru­(CO) 3 X has been reported, photochemistry by dissociation from MLCT states − is not common.…”

“…For PACVD of high metal content films, decomposition of the precursor must result in clean ligand loss to avoid ligand-derived carbon contamination remaining on the surface. Suitable precursors should have a reasonable absorption cross section, exhibit multiple pathways for photolysis, and have high quantum yields for ligand loss to be viable candidates for PACVD. ,, A reasonable absorption cross section is essential to ensure that the precursor will efficiently undergo absorption during the short exposure time in the gas phase experiment. A high quantum yield for ligand loss confirms that the precursor undergoes productive photochemical decomposition pathways following absorption.…”

“…We have previously reported PACVD of Ru on SAMs using three Ru precursors: (η 3 -allyl)­Ru­(CO) 3 Br, CpRu­(CO) 2 CH 3 , and (COT)­Ru­(CO) 3 ( 1a ) . Encouraging deposition results from (η 3 -allyl)­Ru­(CO) 3 Br led us to study the photochemistry of the halide series (η 3 -allyl)­Ru­(CO) 3 X (X = Cl, Br, and I) to investigate the halide dependence on the quantum yield for CO loss from the complex . The primary photoprocess, identified as loss of CO, and the quantum yields were both wavelength- and halide-dependent, with Φ Br > Φ I .…”

Photochemistry of 1,5-Cyclooctadiene Platinum Complexes for Photoassisted Chemical Vapor Deposition

“…Quantum yields were obtained using ferrioxalate actinometry and modified literature procedures. , Potassium ferrioxalate was prepared as reported in the literature . All degassing and purging were done using Ar gas by standard Schlenk techniques.…”

“…The number of photons absorbed was determined using ferrioxalate actinometry as previously reported. 31 Briefly, an aliquot between 2.5−3.0 mL from the irradiated ferrioxalate solution was mixed with twice its volume of developer solution (0.05% phenanthroline (wt %), 0.75 M sodium acetate, and 0.2 M H 2 SO 4 ). The resulting mixture was diluted with deionized water to a volume of either 10 mL or 25 mL.…”