Antioxidants and Light Stabilizers. Part 1. Reactions of an Indolinone Nitroxide and Phenoxy Radicals. X-Ray Crystallographic Analysis of 1-[O-(3,5-di-tert-butyl-4-hydroxy)-benzyl]-1,2-dihydro-2-methyl-2-phenyl-3-oxo-3H-indole and 3,5,3',5'-tetra-tert-butylstilbene-4,4'-quinone