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

Abstract

Quantum yields for disappearance of (COD)­PtMe2 (1a) and (COD)­PtMeCl (1b) were determined at 334 nm in C6D6 solvent. Chain reactions initiated by formation of a methyl radical were proposed to be the cause of quantum yields higher than unity (Φ = 5.52 ± 0.40 for 1a) when the reaction mixtures included C4F9I. The chain reactions were suppressed in the presence of the radical trap 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO), which resulted in measured disappearance quantum yields of Φ = 0.037 ± 0.003 for (COD)­PtMe2 and Φ = 0.44 ± 0.02 for (COD)­PtMeCl at 334 nm. Weak luminescence was observed for 1a and 1b, and it was determined that emissive decay is not competitive with Pt–CH3 bond homolysis. DFT studies enabled assignment of both SBLCT and MLCT transitions in the UV/vis spectra of 1a, while 1b only exhibits MLCT transitions. These effects can be attributed to the symmetry of the molecule and its electronic structure.

Variable Kinetic Isotope Effect Reveals a Multistep Pathway for Protonolysis of a Pt–Me Bond

“…A solution of acid in CH 2 Cl 2 was added by a gas-tight syringe to a cuvette in the spectrometer containing a continuously stirred solution of 1 in CH 2 Cl 2 maintained at 296 K. Reaction progress was monitored by the decay of the absorbance at 288 nm (Figure 1). 57,58 Similar decay behavior was observed for the other two λ max values at 318 and 358 nm. Notably, a minimum of 2.0 equiv of TFAH was required for the protonolysis reaction to near completion (93% conversion, compared to 63% conversion with 1 equiv of acid).…”

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

“…Photoluminescence experiments have previously been included in screening precursors for PACVD suitability. , Complexes exhibiting strong photoluminescence are probably not good precursor candidates, because significant photoluminescence would indicate that emission from an excited state is competitive with the photochemical ligand loss required for PACVD. Samples for photoluminescence experiments were purged with CO to minimize sample degradation by photochemical CO loss during irradiation from the instrument.…”

“…Quantum yields were determined by methods similar to those previously reported. , Briefly, the light from a 500 W Hg­(Xe) arc lamp was transmitted through a bandpass filter, subsequently passing through a cuvette containing the reaction mixture and then the ferrioxalate actinometry cell . Photons absorbed by the reaction mixture were counted by measuring the difference between the actinometry cell behind the reaction mixture versus a separate actinometry cell that was irradiated behind a cell containing only solvent and trapping ligand.…”

“…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.…”

Variable Kinetic Isotope Effect Reveals Multi-step Pathway for Protonolysis of a Pt–Me Bond

“…A solution of acid in CH2Cl2 was added by gas-tight syringe to a cuvette in the spectrometer containing a continuously stirred solution of 1 in CH2Cl2 maintained at 296 K. Reaction progress was monitored by the decay of the absorbance at 288 nm (Figure 1). 57,58 Figure 1. (a) The full absorbance profile of 1 (0.4 mM, dark red) decaying (red to purple) following treatment with TFAD (2.0 equiv).…”