Dehmel was brought by keyboardist Uwe Fahrenkrog-Petersen to join the rock band Nena in 1981.
Fahrenkrog-Petersen and Dehmel had previously been together in a band called Odessa, releasing a self-titled album in 1980.
The band also included Helmut Hirt on vocals, Otto Schneider on drums, Bernd Däumchen on guitar and saxophone, and Andreas Römer on solo-guitar.
In 1986 Nena and Dehmel produced an album for the band Time Boys, under the names of Jay-Dee and Susi K. He also wrote songs and produced soundtracks for German films, and toured frequently with the singer Nina Hagen.
In 1988–89 he also wrote three songs with his girlfriend, Ilonka Breitmeier, for a Bosnian-American pop star called Tinka.