Communication: An n-doped-type light-emitting polymer that emits blue light with a very high photoluminescence efficiency (79%) is reported. Its synthesis and properties are described and its potential for application in polymer light-emitting diodes (PLEDs) has been checked by the construction of a single-layer LED. All polymers commonly used in PLEDs are typical p-doped-type polymers with a greater tendency to transport holes than electrons, this charge imbalance being a key limit to increasing the electroluminescence efficiency of PEDs. This work demonstrates that n-doped-type polymers suitable for PLEDs can be found.