The result is a cascade of signals that brings about a response to the original stimulus. Therefore, it can't trigger sleep, but it might be responsible for the continuity of sleep. That action might occur by the suppression of wakefulness cells. Adding to the complexity, adenosine is not the only natural substance that put us to sleep. Another brain chemical, histamine, may promote wakefulness with an input into the hypothalamus and possibly to c-fos cells.
Drug companies favor the latter because it is so difficult to get a compound into particular cells.
Nevertheless, his team is putting different chemicals into different cells in the hypothalamus to see if they induce sleep in lab animals. We've solved some of the mysteries of sleep, but there's still a great deal we don't know.