Crosslinking-Induced White Light Emission of Poly(Hydroxyurethane) Microspheres for White LEDs

Nonconjugated luminescent polymers with white light emission are promising for a wide range of applications in display and lighting devices, but their preparation remains a big challenge. Herein, a white-light-emitting nonconjugated poly(hydroxyurethane) microsphere (PHUM) synthesized from the crosslinking reaction of trimethylolpropane tri(cyclic carbonate) ether and 1,6-hexanediamine in chloroform is reported. The resultant PHUMs possess uniform sizes ranging from 12.6 to 21.5 mu m. It is proposed that a high crosslinking degree and various hydrogen-bonding strengths induce the formation of carbamate clusters with different sizes and broad distributions, which result in a broad emission spectrum. The cluster-size distribution effect leads to multiple n-pi* transitions from various carbamate clusters via through-space conjugation of carbamates, realizing white light emission. In addition, the application of PHUMs as single phosphor combined with a 365 nm UV chip is also demonstrated, with which a white-light-emitting diode with a high color rendering index of up to 95 is obtained. This work confirms that crosslinking can induce multiple emissions, which provides a new clusteroluminescence and polymerization-induced emission system for tunable luminescence emission.