NEW YORK — Diet Pepsi is sending a valentine to soda lovers, now that the soft drink’s staying power has been improved with a new sweetener.

Starting at the end of January, PepsiCo Inc. will begin airing TV ads with the tag line ‘‘Love Every Sip,’’ along with the rollout of special-edition silver cans featuring the blue-and-red Pepsi logo in a heart shape. The company is working with designers to introduce other special designs later in the year, as well.