Van Gogh chose sunflowers to experiment with color. He painted a series of sunflower paintings which were intended for the walls of his studio. He was preparing for the arrival of his friend (and fellow artist), Eugene Gaunguin. The sunflower paintings now represent a time in France and the friendship between Van Gogh and Eugene Gauguin.
Van Gogh painted his series of sunflowers for Paul Gauguin, not for Eugene (just a little correction). He experienced with color indeed, and yellow was his favorite color. Sunflowers are his trademark as it seems, even Gauguin acknowlegded that, even if they weren't the best friends... With these paintings he tried to put his emotions in it, and to paint the circle of life. He took fresh flowers, put them in a vase, and pushed himself to paint it very fast, because they would only stay good for a few hours... It is said that van Gogh in his period of Arles tried to paint as a Japanese painter, with bright colors, no shadows, contrast in his color... Also the circle of life, or reincarnation. He tried to express that in his painting, the birth and death, and rebirth, of the sunflower.