A series of liquid crystalline (LC) homopolymers of poly{11-[4-(4-butylphenylazo)phenoxy]undecyl methacrylate}containing an azobenzene mesogen with different degrees of polymerization were synthesized by using the atom transfer radical polymerization (ATRP) method. The homopolymers were prepared with a range of number-average molecular weights from 6100 to 23 500 with narrow polydispersities of less than 1.17. Thermal investigation showed that the homopolymers exhibit monolayer smectic A, smectic C, and an unknown smectic X phases. The transition temperatures increase slightly with the increase of the molecular weights and level off at around 21 500. Novel amphiphilic LC-coil diblock copolymers with a defined length of a flexible poly(ethylene glycol) segment as the hydrophilic coil were also prepared by the ATRP method. The LC-coil diblock copolymers exhibit narrow polydispersities of less than 1.11. Morphologies of the thin films of the block copolymers were investigated by using transmission electron microscopy (TEM). Microphase separation with small size in the range of 10−20 nm (nanoseparated structures) was observed. Different photophysical and photochemical behaviors were observed between annealed homopolymer and block copolymer films, which is thought to be caused by the formation of nanostructures of the block copolymers.

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Colloidal nanocrystal quantum dots (QDs) are solution-processable chromophores with size-tunable bandgaps, high photoluminescence (PL) quantum efficiency (QE), excellent photostability, narrow emission line widths (< 30 nm), and large spin-orbit coupling. These factors make them good candidates for use in next-generation thin-film optoelectronic devices. Indeed, colloidal QDs are currently being explored for use in photovoltaics, [1][2][3][4] photodetectors, [5,6] and light emitting diodes, [7][8][9][10][11][12][13][14][15][16][17][18] often in hybrid structures that incorporate both QDs and conjugated polymers or small-molecule organic semiconductors. Despite the potential advantages of using QDs as emitters, early QD light-emitting diodes (QD-LEDs) exhibited low efficiencies, and often produced broad voltage-dependent emission with spectral contributions from both the QDs and the organic host materials. However, drawing from lessons learned from the field of all-organic LEDs, the MIT group reported a multilayer LED structure incorporating a monolayer of CdSe/ZnS core/shell QDs sandwiched between small molecule hole and electron transport layers. These devices exhibited a maximum external quantum efficiency (Q ext ) of ∼ 0.5 % and a luminous efficiency (LE) of 1.9 cd/ A at a brightness of 100 cd/ m 2 , although pure emission spectra at high brightness were not achieved in the initial report. [8,16] With subsequent refinements, the same authors have achieved maximum Q ext of > 2 % and luminous power efficiency (LPE) > 1 lm/W.[17]Recently, we reported an alternative strategy for QD-LED fabrication that allows for independent control of the QD and hole-transport layer (HTL) thicknesses by spin-coating the QD layer onto a thermally cross-linked HTL.[18] Using this flexible fabrication strategy, we demonstrated that graded structures comprising multiple hole-transport and injection layers could be used to further improve Q ext of the devices. The best devices exhibited good efficiency (Q ext > 0.8 % at 100 cd/ m 2 ), narrow EL spectra (∼ 30 nm FWHM) and maximum brightness in excess of 1000 cd/ m 2 . However, because of the high turn-on voltage for our first QD-LEDs, the LPE was not high.Herein, we describe how a substantial improvement in QD-LED performance, especially the LPE, can be obtained both by using an improved polymer hole-injection layer (HIL)/ HTL structure and by performing a thermal annealing of the QD layer prior to the final deposition of the organic electrontransport layer. In particular, the annealing step results in a significant performance improvement with these devices. In order to lay the scientific groundwork for future improvements in QD-LED performance, we characterize the changes in the chemical, photophysical, and electronic properties of the structures that occur due to the annealing process.

A new oxygen sensor, compound 2, was synthesized through a chemical modification of a popularly used oxygen sensor of platinum(II)-5,10,15,20-tetrakis-(2,3,4,5,6-pentafluorophenyl)-porphyrin (PtTFPP). The new sensor compound 2 possesses four crosslinkable methacrylate functional moieties, enabling it to be polymerized and crosslinked with other monomers for polymer sensing film (also called membrane) preparation. Using this characteristic, compound 2 was covalently bonded to hydrophilic poly(2-hydroxyethyl methacrylate)-co-polyacrylamide (referred to as PHEMA to simplify) and hydrophobic polystyrene (PS) films. To better understand the advantages and disadvantages of chemical crosslinking approaches and the influence of polymer matrices on sensing performance, PtTFPP was physically incorporated into the same PHEMA and PS matrices to compare. Response to dissolved oxygen (DO), leaching of the sensor molecules from their matrices, photostability of the sensors, and response time to DO changes were studied. It was concluded that the chemical crosslinking of the sensor compound 2 in polymer matrices: (i) alleviated the leaching problem of sensor molecules which usually occurred in the physically doped sensing systems and (ii) significantly improved sensors' photostability. The PHEMA matrix was demonstrated to be more suitable for oxygen sensing than PS, because for the same sensor molecule, the oxygen sensitivity in PHEMA film was higher than that in PS and response time to DO change in the PHEMA film was faster than that in PS. It was the first time oxygen sensing films were successfully prepared using biocompatible hydrophilic PHEMA as a matrix, which does not allow leaching of the sensor molecules from the polymer matrix, has a faster response to DO changes than that of PS, and does not present cytotoxicity to human lung adenocarcinoma epithelial cells (A549). It is expected that the new sensor compound 2 and its similar compounds with chemically crosslinking characteristics can be widely applied to generate many interesting oxygen sensing materials for studying biological phenomena.