LOS ANGELES — Rob Thomas’ new CD, “Cradlesong,” reveals a more complex side of the singer: Themes of despair, and even death, are explored in the songs.

While it may suggest a darker mood, the 37-year-old, best known as the frontman for Matchbox Twenty and hits like his “Smooth” collaboration with Santana, says it simply reflects life from a more mature vantage point.

“As you get older, your themes change and the things that are important to you change, your focuses change,” said Thomas as he talked about his sophomore CD, which was released last month.

“And so there’s a lot of stuff on here about — obviously, not about being old, but just about being older. And the things that were important to you maybe not being as important to you now, and you have a whole new set of burdens to bear as you take on the responsibility of family, the responsibility of wanting to be an adult — not just getting older, but being an adult, which are two separate things.”

The first single, “Her Diamonds,” was written for his wife, Marisol, who suffers from an autoimmune disease. It deals with his sadness over her health challenges (the music video features Alicia Silverstone).

Thomas also mused about his starkly dramatic album cover, which features a haunted-looking Thomas, his face half-shadowed, embellished by artwork. Thomas says he was inspired by French surrealist paintings.

“Some people hate it, and I think I love that. I can’t remember the last time that people have cared about an album cover enough to hate it. So I think I’ve done something right,” he said. “But I think it’s a striking image.”

Thomas begins rehearsals for his tour in support of “Cradlesong” in September. But even in the midst of developing his solo career, Matchbox Twenty isn’t far from his mind. Thomas said before he hits the road, he plans to meet with his bandmates and start hashing out ideas for the next album to keep their “forward momentum” in high gear.