Editing the leading on a created textFrame

Hi,

I have no idea why the following code will not work.

The text displays in the correct place with the correct contents but i cannot get the leading to change.

var textInfo = app.activeDocument.textFrames.add();

textInfo.name = "textInfo";

textInfo.position = [30,-30];

textInfo.contents = "A";

textInfo.autoLeading = false;

for(var i = 0; i<app.activeDocument.textFrames["textInfo"].textRange.characters.length; i++){

    app.activeDocument.textFrames["textInfo"].textRange.characters.characterAttributes.leading = 18;

    redraw();

    $.writeln(app.activeDocument.textFrames["textInfo"].characters.characterAttributes.leading);

    }

I have also tried textInfo.leading = 18; with no luck.

The write line function at the end is reading the correct leading but the line above is not editing it.

Adobe illustrator CS6, Mac OS 10.6, Javascript/extendscript

Also, not too sure what auto leading does so have tried both with and without.

Thanks,

Tom