You should be using post_class
(and body_class
for that matter) but you don’t need it for this. Alter your Loop on your home page to conditionally format the first post.
$first = (!is_paged()) ? true : false;
if (have_posts()) {
while (have_posts()) {
the_post();
if ($first) {
// code to format the first post
$first = false;
} else {
// code to format all the other posts
}
}
}
If all you need is a small change that can be made via CSS then you can pass post_class
a parameter.
$first = (!is_paged()) ? 'is_first' : 'not_first';
if (have_posts()) {
while (have_posts()) {
the_post();
echo '<div ',post_class($first),'>';
// the rest of your Loop
echo '</div>';
$first="not_first";
}
}