create dynamic property after creating instance of c# class

You could use Reflection:

using System;
using System.Reflection;

public class Foo
{
    public string Bar { get; set; }
}

public class Program
{
    static void Main()
    {
        string name = "Foo";
        string property = "Bar";
        string value = "Baz";

        // Get the type contained in the name string
        Type type = Type.GetType(name, true);

        // create an instance of that type
        object instance = Activator.CreateInstance(type);

        // Get a property on the type that is stored in the 
        // property string
        PropertyInfo prop = type.GetProperty(property);

        // Set the value of the given property on the given instance
        prop.SetValue(instance, value, null);

        // at this stage instance.Bar will equal to the value
        Console.WriteLine(((Foo)instance).Bar);
    }
}