Brian McKnight. (Joe Corrigan/GETTY IMAGES)

His decision to do so has sparked a conversation between McKnight and his fans on Twitter about the music business and the state of R&B.

McKnight was asked to write the song by the Web site, the singer said on Twitter. The company was inspired by his song “iFUrReadyToLearn,” an explicit slow jam/sex education course that launched a thousand headlines. McKnight said the song was a parody.

Superficially, this latest development is just another funny and slightly odd situation to see McKnight — perhaps best known for his wedding anthem “Back At One” — in. But the singer has also been forced to defend his choice to create the adult site theme song on Twitter, explaining that this is just part of the music business now.

Here are a few of the reasons he provided for doing the song:

— “as a business man I can’t ignore the opportunities that r out there especially when it’s all in fun.”

— “they asked me they appreciate creativity and are willing to patronize it.”

— “guess u thought I made music for fun and not for a living”

— “integrity won’t pay the mortgages I will ask all of u how many of u would do your job for no pay?”

— Responding to a “true fan” who disapproves, “really then y are record sales for everyone so low y weren’t u on my timeline til now”

The song has also started an interesting back and forth about the current state of R&B.

Twitter user B. Young, who in his profile says he’s a marketing rep for Sony Music Entertainment, told McKnight, “yo I have some beats/writers if you wanted attention for your music.”

McKnight responded, “and that just goes to show u have no idea what this business is about.” Young later replied, “instead of making these Xrated Headlines. Let’s concentrate on bringing RnB back.”

Erika Ramirez at Billboard’s the Juice blog recently wrote about McKnight’s first NSFW song and the decline of interest in R&B: “Aside from Beyoncé and Usher (recently), R&B artists and ballads aren’t effortlessly transitioning from the R&B charts to the mainstream charts [like] they once did, unless they’re assisted by a hip-hop feature or a Chris Brown hook.”

Because of this, it’s hard to fault McKnight for writing explicit songs if they pay the bills and allow him to keep creating R&B. It’s also doubtful that his more risque material will bleed into his mainstream work, as his recent show at the Blue Note, which was naughty song free, seems to indicate.

For reasons that should be very clear, I cannot directly link you to the new song. The entire track can be heard on the adult Web site’s NSFW blog, which is linked to in this SFW tweet.