What do you mean by large _concept_ application? If you mean large or famous projects in production, Yii 2.0 was just released so there aren't many.

For 1.1 there are some:

https://www.facebook-studio.com/, http://2gis.ru/, http://itop.fm/, https://www.humhub.org/, http://www.x2engine.com/, http://zurmo.org/, https://www.rebilly.com/, http://buildwithcraft.com/