Molecular Devices

Bipolar light-emitting junctions

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Science  16 Jun 2017:
Vol. 356, Issue 6343, pp. 1135-1136
DOI: 10.1126/science.356.6343.1135-g

Molecular junctions formed from Ru(bpy)3 oligomers (bpy, 2,2′-bipyridine) transition with increasing thickness from transporting electrons to emitting light. Tefashe et al. used electrochemical deposition to grow Ru(bpy)3 oligomers along with PF6 counterions on conducting carbon, which was then capped with conducting carbon to form a junction. Films thicker than 4 nm emitted light at wavelengths between 600 and 900 nm for biases above 2.7 V. Unlike previous devices based on Ru(bpy)3, the emission is bipolar (occurs for both positive and negative bias) and has a rapid onset (5 ms) and long persistence (10 hours). The authors argue that both hole and electron injection occur through a resonant process involving a metal-to-ligand charge transition.

J. Am. Chem. Soc. 10.1021/jacs.7b02563 (2017).

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