Hi Harshal,
To define a property binding on a control its preferable to set the path of your associated model. You can assign the path to the var variable1 to an object literal later set it to the global model and notice the changes to the object literal.
var variable1 = {
"value" : "hello world!"
}
var oModel = new sap.ui.model.json.JSONModel();
oModel.setData(variable1);
sap.ui.getCore().setModel(oModel); //Global Context
As model can only listen for changes I believe you cannot assign to random variable and listen to changes.
Regards,
Ajain