how to get the value of checkbox currently unchecked in multi select dropdown list?

I am have created a multi select filter. For each of the options selected the new div element will be created with it's id is the value of checkbox selected. Till here it's working fine. But now I want to remove those div who's options(checkboxes) are un selected. I tried the below,

 if(!($(this).is(":checked"))){
      alert('is un-checked: ' + $(this).val());
   }

but it's not working. Giving value of null. Can anyone please suggest me how can I achieve this?