Highly Efficient UV Organic Light‐Emitting Devices Based on Bi(9,9‐diarylfluorene)s

Abstract

The lasers used were a XeCl laser operating at 308 nm, s pulse » 30 ns (Lambda Physik, EMG 201 MSC), and an Nd:yttrium aluminum garnet (YAG) laser, operating at the second harmonic, k = 532 nm, s pulse » 5 ns (B. M. Industries, Serie 5000).Experimental Methods: For the macroscopic mechanical actuation of the films, the laser beams were weakly focused onto the front surface of the film so that the entire surface area of the film was homogeneously irradiated (spot area: 1.5 mm 2.5 mm). A digital camera, placed at an angle of~85 to the normal to the surface, was used for monitoring the bending of the films.In the fluorescence experiments, the UV laser beam was weakly focused almost perpendicularly onto the sample in a 1.2 mm diameter spot using a quartz spherical lens (f = +500 mm). The green laser beam was also weakly focused onto exactly the same area where the UV beam is focused, almost perpendicularly to the sample. Irradiation of the samples was performed in ambient atmosphere. The fluorescence of the stable trans MC photoproducts was probed by excitation with laser pulses of 532 nm of very low fluence (F laser £ 4 mJ cm ±2 ). Photoproduct formation by the probe beam was negligible, and all recorded fluorescence can be assumed to derive exclusively from photoproducts formed by the preceding pump laser pulses. A relatively long delay (of the order of several seconds) between the pump and probe pulses was employed for ensuring that the fast-formed, metastable isomers had turned into the final/stable isomers. On the other hand, the monitoring of the metastable photoproducts was achieved by collecting the emission signals from the samples with zero delay with respect to the pump laser pulses.The induced emission was collected by an optical fiber placed nearly perpendicular to the substrate and~1±2 cm from its surface. An x±y micrometer ensured accurate positioning of the optical fiber relative to the irradiated spot. The light from the fiber was spectrally analyzed in a 20 cm grating spectrograph and recorded by a gated optical multichannel analyzer (OMA III system, EG&G PARC Model 1406). A gate time value of 1 ls was applied. Highly Efficient UV Organic Light-Emitting Devices Based on Bi(9,9-diarylfluorene)s** By Teng-Chih Chao, Yu-Ting Lin, Chen-Yu Yang, Tsung Shi Hung, Hung-Chieh Chou, Chung-Chih Wu,* and Ken-Tsung Wong*The rapid advancement of organic light-emitting devices (OLEDs) in recent years has extended the emission wavelengths over the whole visible range and has enabled realization of full-color OLED displays. Extending the emission of OLEDs into even shorter ultraviolet wavelengths, however, has not progressed as well, although compact and efficient UV emitters would find many uses in biological/fluorescent sensors, [1±2] in full-color displays by generating blue-to-red emission through pumping luminescent materials, [3] or in high-density information storage devices. [4±6] In addition, wide-gap materials are also of increasing importance in triplet emitters for electrophosphorescence. [7±9] In th...

Photophysical properties of heteroaromatic ring-fused (di)benzosiloles

“…Organic solid chromophores whose emission maxima appear below 400 nm are highly desirable as emitters for UV OLEDs as well as host materials for triplet dopant emitters. For example, Wu, Wong and co-workers [54,55] developed bi(9,9-diarylfluorene)s as wide-gap materials, which exhibited efficient fluorescence in a thin film with emission maxima at 392 nm and high quantum yields ranging from 0.57 to 0.66. Therefore, it is remarkable that the absolute quantum yields of 6 and 7 in microcrystals reached 0.51 with an emission maximum of 395 nm and 0.70 with 396 nm, respectively.…”

Blue organic light-emitting diodes using novel spiro[fluorene-benzofluorene]-type host materials

“…Mp 371.8 C. 1 14 (d, 2H, Ar-CH-fluorene), d 7.14-7.13 (d, 1H, Ar-CH-benzene), d 6.89-6.88 (d, 2H, Ar-CH-fluorene), d 6.88 (d, 1H, Ar-CH-benzene). 13 …”

“…Although a large number of valuable red and green emitters that satisfy the requirements for OLEDs have been developed, efficient and stable blue emitters are still rare and have been the subject of considerable interest [1,2]. Major focus has been on various material systems, including anthracene [3][4][5], distyrylarylene [6][7][8][9][10][11], fluorene [12,13] and tetra(phenyl)silyl derivatives [14,15].…”

Efficient near ultraviolet organic light-emitting devices based on star-configured carbazole emitters

“…For example, OLEDs with emitter of 4,4-N,N-dicarbazole-biphenyl (CBP) showed the maximum external quantum efficiency (s max. ext ) of 1.25% [12], comparing with 2.8% of tri(p-terphenyl-4-4-yl)amine (p-TTA) emitter and 3.6% of bi(9,9-diaryfluorene) emitter [13,14].…”