Complex sentence: In April 2008 Hockney donated the painting to the Tate, saying, I thought if I'm going to give something to the Tate I want to give them something really good.
Split into simpler sentences: In April 2008 Hockney donated the painting to the Tate. Hockney said I thought if I'm going to give something to the Tate I want to give them something really good.