Near‐Infrared Electroluminescent Light‐Emitting Devices Based on Ethyne‐Bridged Porphyrin Fluorophores

Abstract

For the emitters following the Fowler±Nordheim (FN) theory, the plot of ln(J/E 2 ) versus E ±1 gives a straight line and its slope, ± (Bu 3/2 /b), determines the FN enhancement factor b, where E is the applied field, u is the work function, and B is a constant. The inset in Figure 5 displays the corresponding FN plot at a separation of 150 lm, showing a linear relationship and revealing that electron emission from the tips of the nanowires follows FN behavior. Here, we define the turn-on field and the threshold field as the electric fields required to produce a current of 10 lA cm ±2 and 10 mA cm ±2, respectively. The results demonstrate that the prepared W 18 O 49 nanowires had a turnon field of 2.6 ± 0.1 V lm ±1 and a threshold field of 6.2 V lm ±1 .The threshold field of W 18 O 49 nanowires is close to that reported for open-ended C nanotubes (~5 V lm ±1 ) [3] and lower than that of needle-shaped SiC nanorods (~8.5 V lm ±1) or MoS 2 nanoflowers (7.6±8.6 V lm ±1 ), [19,20] indicating that the prepared W 18 O 49 nanowires are excellent field emitters. In summary, quasi-aligned single-crystalline W 18 O 49 nanotubes or nanowires were successfully prepared under different atmosphere pressures. The diameters of the nanotubes were 150±350 nm, while those of the nanowires were in the range of 20±100 nm. A deficiency in vapor supply plays an essential role in the nucleation of tubular nanostructures. Field-emission measurements showed a threshold of 6.2 V lm ±1 for the W 18 O 49 nanowire films, indicating that they are excellent field emitters. The prepared tungsten oxide nanotubes or nanowires have a great potential for photochromic or electrochromic applications. ExperimentalThe experiments were conducted in an infrared irradiation±heating furnace connected to a high-vacuum system. Tungsten foils (15 mm 15 mm 0.1 mm) were used as heating targets. A Ta wafer (10 mm 10 mm) was laid under the W foil at a 3 mm distance and used as substrate. The W foils were heated to 1000±1050 C, while the temperature of the Ta substrate was about 650 C. Heating continued for 1 h. In the synthesis of the nanotubes, the chamber air pressure was maintained at 0.2 torr for the first 20 min, and then increased to 10 torr for the remaining 40 min. In the synthesis of nanowires, the air pressure in the chamber was kept at 10 torr for the whole process. When the chamber cooled to room temperature, the upper surface of the Ta substrates was entirely covered with a dark blue film. A field-emission SEM (JSM-6700F) was used to observe the morphology of the products. XRD spectra of the prepared nanostructures were recorded on a RINT2200 X-ray diffractometer using standard Cu Ka radiation. Further structural characterization was performed on a highresolution TEM (JEM-3000F) at 300 kV. The chemical composition of the nanostructures was detected using an EDS apparatus attached to a TEM.

Benefits of using BODIPY–porphyrin dyads for developing deep-red lighting sources

“…To this end, we took advantage of our mature experience in the synthesis of BODIPYporphyrin dyads and their implementation in solar cells [16][17][18][19] to trapping process at the porphyrin, (ii) there is an almost quantitative ET process from the BODIPY to the porphyrin, (iii) there is a lack of phase separation between both components in thin films as they are linked, and (iv) porphyrins are considered as one of the best candidates for developing narrow emission deepred OLEDs. 2,[20][21][22][23][24][25][26][27] On the other hand, LECs are ideal devices to demonstrate our concept, as they are single layer devices based on a single active component, allowing to settle clear relationships between molecular design and device performance. [8][9][10] In addition, this work provides, to the best of our knowledge, the first example of using this family of dyads in lighting schemes, demonstrating the benefits that state from their unique features.…”

“…[1][2][3][4][5] This field is mainly driven by their ease of modification to enhance light-harvesting and photoluminescence (PL) properties based on an efficient energy and/or electron transfer process from moieties attached at the periphery to the porphyrin core.This feature of dyad-like porphyrins is of utmost relevance for lighting schemes, since it could open a new avenue to decouple charge transport and emission processes by only using one active compound. This is more critical in light-emitting electrochemical cells (LECs) than in OLEDs, in which the charge transport is not performed by the emitter, but by a multilayered device architecture.…”

“…[1][2][3][4][5] This field is mainly driven by their ease of modification to enhance light-harvesting and photoluminescence (PL) properties based on an efficient energy and/or electron transfer process from moieties attached at the periphery to the porphyrin core.…”

Meso-Linked Multiporphyrins as Model for Light Harvesting Systems: Review

“…However, these porphyrin arrays show very weak ground-state electronic interactions between the porphyrin units. Various linear types of meso-to meso acetyleneand butadiyne-bridged multiporphyrins have also been reported and their photo physical and electrochemical properties have been determined [36][37][38]. In contrast to the arene-bridged porphyrin arrays, these types of multiporphyrins exhibit strong ground-and excitedstate interporphyrin electronic coupling.…”

“…In the covalently linked porphyrin arrays, a variety of linkages such as ethyne [36,37], polyyne [38][39][40], ethylene [41], alkane [42,43] and aromatic entities [44][45][46] have been used to bridge the individual porphyrins. Lindsey et al have reported the synthesis of numerous phenylene-and diphenyl ethynyl-bridged multiporphyrins for mimicking the biological light-harvesting antenna systems and their photo physical properties have been studied [46][47][48].…”