Degradation of blue-phosphorescent organic light-emitting devices involves exciton-induced generation of polaron pair within emitting layers.

Degradation of organic materials is responsible for the short operation lifetimes of organic light-emitting devices, but the mechanism by which such degradation is initiated has yet to be fully established. Here we report a new mechanism for degradation of emitting layers in blue-phosphorescent devices. We investigate binary mixtures of a wide bandgap host and a series of novel Ir(III) complex dopants having N-heterocyclocarbenic ligands. Our mechanistic study reveals the charge-neutral generation of polaron pairs (radical ion pairs) by electron transfer from the dopant to host excitons. Annihilation of the radical ion pair occurs by charge recombination, with such annihilation competing with bond scission. Device lifetime correlates linearly with the rate constant for the annihilation of the radical ion pair. Our findings demonstrate the importance of controlling exciton-induced electron transfer, and provide novel strategies to design materials for long-lifetime blue electrophosphorescence devices.

Graphene-based electrochromic systems: the case of Prussian Blue nanoparticles on transparent graphene film.

Prussian Blue nanoparticles were electrodeposited on transparent grapheme film, which showed a promising electrochromism with response times in the range of 3.3-38 s.

Designed synthesis of multi-electrochromic systems bearing diaryl ketone and isophthalates.

New multi-electrochromic systems have been developed through the combination of a diaryl ketyl radical system with isophthalate-based electrochromic materials. The location of the isophthalate group in compounds is very critical to obtaining different colors in the multi-electrochromism.

Designed synthesis of ferrocenylanthraquinones and their bifunctional electrochromic properties.

New bifunctional electrochromic systems were developed by combination of reductive anthraquinone with oxidative ferrocene redox systems. The resultant ferrocenylanthraquinones demonstrated enhanced stability in electrochromic performance through the concomitant reductive electrochromism and oxidative counting action. The displayed colors were dependent on the position of the ferrocenyl group.

Molecular design and preparation of bis-isophthalate electrochromic systems having controllable color and bistability.

New electrochromic systems based on bis-isophthalates were designed and prepared. They showed electrochromism behavior by two-electron reduction. The displayed colors showed greatly enhanced bistability and were dependent on the length of the conjugated bridge between the two isophthalate groups. We believe that the connection of two electrochromic systems with a conjugated bridge is a good basic strategy to obtain new bistable electrochromic systems.