Is it possible to easily simplify the difference of conjugate pairs?

In particular, if there’s just a single variable, then

`FullSimplify[a - Conjugate[a]] `

`2 I Im[a]`

But trying to do the same thing with a slightly more complex expression fails:

`FullSimplify[a Conjugate[b] - Conjugate[a] b] `

`a Conjugate[b] - Conjugate[a] b`

I have found one solution (answered below) but it relies on a `FullSimplify`

which doesn’t seem very optimal.