The customize_controls_print_scripts action hook is triggered within the <head></head> section of the theme customizer screen. By default, the function print_head_scripts() is added to this action with a priority of 20.
This hook functions similarly to the wp_head action hook, but only affects the theme customizer screen. Generally, when using the Theme Customization API, you are better off hooking into wp_head instead.
<?php
add_action('customize_controls_print_scripts', 'your_function');
?>
See Theme Customization API and Plugin API - Actions for more detail.