WP Admin Bar - PHP inside of title Argument

I wish to echo the current theme in text in my WP Admin Bar sub menu.

Here is what some of my php looks like for the custom admin bar link I created:

$wp_admin_bar->add_menu( array(
'id' => 'ab-sh-current-theme',
'parent' => 'my_custom-menu',
'title' => 'Theme Name',
'href' => false
) );

I wish to insert a snippet of PHP where you see Theme Name, like so: 'title' => 'Theme Name',

Get Current Theme WP Codex
Add Menu Function Reference

<?php
    $theme_name = get_current_theme();
    echo $theme_name;
?>