First go to Graphene Options –> Display –> Column Options and select One Column (First one) mode.
Then, create two blank pages, one for static frontpage and another for blog page with two columns.
Go to WordPress settings –> Reading settings and select first page you’ve created as Static Frontpage and Blog page as Posts page. So that your posts page will have two columns with sidebar and the single blog page will have only post container without any sidebar.
You may follow this post to create static front page and posts page. – http://www.prasannasp.net/how-to-enable-homepage-panes-in-graphene-theme/
Additionally, if you wish you can redirect your homepage to posts (blog) page using any page redirect plugin.
