"It's very, very emotional. It's the first time I suppose she's doing a part as a lead actress as an adult on her own and she's absolutely extraordinary," he said.
"I thought, maybe this is for people who remember emigration but all the young people who came from the publishers and agency in London, they were all in tears of the choice she had to make.
"Was she going to stay in Ireland or was she going to go back to Brooklyn and the guy, the American actor Emory Cohen plays it as pure charm. He'll do anything to win her."
"Domhnall Gleeson in Ireland plays it the other way around (to Cohen).
"He is just so sincere, so honest, so decent that he would mean pure stability and he sort of needs her and she can see that every word he says is true. So they're playing the opposite ways against each other and she has to decide which way to go," Toibin told Newstalk's Pat Kenny.
Directed by John Crowley, (Boy A, Closed Circuit) Brooklyn doesn't have a set release date yet - we just know it's coming sometime in 2015 - so I'll keep hunting about for music clues. The script, based on Toibin's novel, was written by Nick Hornby.