Don't use [`ToString`](http://reference.wolfram.com/language/ref/ToString) (and especially, don't use a single argument [`ToString`](http://reference.wolfram.com/language/ref/ToString)). Instead, just use expressions instead of strings:

	Subscript[θ,n]==π/2

[![enter image description here][1]][1]


  [1]: https://i.sstatic.net/kqXWC.png