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the observed PL transients. The non-exponential decay of the undoped sample originates from spatial diffusion of excitation.[20] Non-radiative energy transfer from 1 to the dye further reduces the lifetime of the host so that the doped host has a faster PL transient. The re-absorption of PL from the host by the Coumarin would not affect the dynamics of the host PL confirming that the energy transfer mechanism is non-radiative. A DCM-doped [21] 1 cell was also prepared in which the PL from the host was completely quenched. A PL excitation experiment shows that the DCM is indirectly excited via the host, further confirming non-radiative energy transfer from 1 to the dye.In conclusion, we report a new class of calamitic chiral nematic glassy liquid crystals with a unique spectrum of properties giving rise to circularly polarized light emission with an unusually high polarization ratio (maximum = 16:1) across a surprisingly broad bandwidth (> 110 nm). The average ratio (> 8:1) is the highest reported so far. The PL spectrum overlaps the unusually broad 1D photonic stop band. This highly circularly polarized light is generated from a sample (in the helical Grandjean planar texture) only 3 lm thickÐan order of magnitude thinner than state-of-the-art materials. A guest± host cell, which is indirectly excited by non-radiative energy transfer from the luminescent chiral nematic host to a guest dye, shows an even higher ratio of circular polarization (maximum = 19:1) with quenching of emission from the host. The results obtained so far are for PL. However, the hole mobility of this new class of materials is also unusually high (2 10 ±4 cm 2 V ±1 s ±1 at room temperature) and should facilitate the fabrication of electrically pumped devices. ExperimentalCells having planar orientation are prepared with one or two rubbed polyimide alignment layers. The cells are filled by vacuum induced flow of the liquid crystal in the isotropic phase. Slow cooling results in a uniform Grandjean planar texture and the formation of a right-handed helix. An unpolarized xenon light source is used for the transmission experiment. A continuous wave GaN laser at 405 nm is used to excite the samples. PL is detected from the rear of the cell using an Ocean Optics spectrometer. A high-pressure xenon lamp dispersed through a monochromator was used for the PL excitation measurements. The frequency doubled output at 395 nm from a femtosecond mode-locked titanium sapphire laser operating at 82 MHz is used to excite time-resolved PL. The PL was filtered using a subtractive double monochromator and detected using a synchroscan streak camera system. The overall time resolution of the system is 3 ps.Received

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