Halogen bond is emerging as a significant driving force for supramolecular self-assembly, and has aroused great interest during the last two decades. Among the diverse halogen-bonding donors, we take notice of the ability of 1,4-diiodotetrafluorobenzene (1,4-DITFB) to co-crystallize with diverse halogen-bonding acceptors in the range from neutral Lewis bases (nitrogen-containing compounds, N-oxides, chalcogenides, aromatic hydrocarbons and organometallic complexes) to anions (halide ions, thio/selenocyanate ions and tetrahedral oxyanions), leading to a great variety of supramolecular architectures such as discrete assemblies, 1D infinite chain and 2D/3D networks. Some of them act as promising functional materials (for instance, fluorescence, phosphorescence, optical waveguide, laser, nonlinear optics, dielectric and magnetism), and soft materials (e.g. liquid crystal and supramolecular gels). Here we focus on the supramolecular structures of multicomponent complexes and their related physicochemical properties, highlight representative examples, and show clearly the main directions which remain to be developed and improved in this area. From the point of view of crystal engineering and supramolecular chemistry, the complexes summarized here should give helpful information for further design and investigation on the elusive category of halogen-bonding supramolecular functional materials.
b S Supporting Information ' INTRODUCTIONPhosphorescent organic light-emitting devices (PHOLEDs) have attracted tremendous research interests owing to the spinÀ orbit coupling interactions of heavy metals, resulting in the harvest of both singlet and triplet excitons to give the approaching 100% internal quantum efficiency theoretically. 1À4 However, it is a prerequisite for high-performance PHOLEDs to blend the triplet emitters of heavy-metal complexes into host matrixes to reduce their concentration-quenching effect. Recently, considerable progresses have been achieved in small molecular host materials based blue PHOLEDs in terms of brightness, power efficiency, and durability. 5À8 However, small-molecule based devices require complex coevaporation techniques, high vacuum, and tedious and precise control process during device fabrication, thus greatly hindering the success of product development and commercialization. In contrast, solution process methods, such as spin-coating, inkjet printing, or screen printing, show more advantages of easier fabrication process and lower cost with phosphorescent polymer light-emitting diodes (PPLEDs). 9 In this context, the key issue is to develop the excellent polymer host materials for PPLEDs, especially for blue PPLEDs.Similar to small molecular host materials, high triplet energy (E T ) levels are crucial for suitable polymer host materials to effectively prevent reverse energy transfer from emitters to hosts and confine triplet excitons on the triplet emitters in PPLEDs. 10À12 In general, π-conjugated polymers usually have low E T levels, which are not suitable as host materials for blue and green phosphorescent heavy-metal complexes, 13,14 such as poly(2,7-fluorene)s and its derivatives which are the widely used π-conjugated polymer host materials possess low E T of 2.15À2.3 eV. 15,16 One effective method to increase the E T levels is to design the nonlinear π-conjugated polymers via the method, limiting the delocalization length of carriers and excitons. However, the obtained π-conjugated polymers, such as poly(3,6-carbazole)s (E T = 2.53À2.6 eV), 17,18 poly(3,6-fluorene)s (E T = 2.58 eV), 19 poly(3,6-silafluorene)s (E T = 2.55 eV), 20 and poly(m-phenylene) derivatives (E T = 2.64 eV) 21 still have too low E T levels to act as efficient host materials for typical blue electrophosphorescent emitters, such as bis[(4,6-difluorophenyl)pyridinato-N, C 2 (picolinato)iridium(III) (FIrpic) (E T = 2.65 eV). Other π-conjugation-interrupted technique also provides a useful strategy to improve the E T levels of polymer host materials through the introduction of sp 3 -hybrized carbon, silicon, or oxygen. 22 However, there are still rare polymer host materials for blue electrophosphorescent emitters up to date.With respect to π-conjugated polymers, π-stacked polymers as supramolecular semiconductors exhibit the unique carrier and exciton features in the applications of various polymer semiconducting devices. 23,24 The design of π-stacked polymers opens another way to develop the ...
A series of n-type fulleropyrrolidine derivatives as the acceptors, including Th-C60, PFTh-C60, and OPFTh-C60, have been synthesized via the key step of the typical Prato reaction to investigate the steric hindrance effect of various phenylfluorenyl moieties on the electronic structures, aggregate morphologies, and device performances of solar cells. Conjugation-interrupted linkage obviously does not change the energy bandgaps and lowest unoccupied molecular orbital (LUMO) energy levels in PFTh-C60 and OPFTh-C60 models with respect to that of precursor Th-C60 according to UV–vis spectra and cyclic voltammetry. In contrast, dramatically different phase separation behaviors in the bulk heterojunction (BHJ) film blending with poly(3-hexylthiophene) (P3HT) were observed by atomic force microscopy. A prototype OPFTh-C60-based BHJ polymer solar cell (PSC) with the configuration of ITO/PEDOT:PSS/P3HT:OPFTh-C60 (1:1) (200 nm)/Ca/Al has the performance with the short-circuit current (I sc) of 8.68 mA/cm2, open-circuit voltage (V oc) of 0.63 V, fill factor of 0.51, and power conversion efficiency of 2.80%, better than that in PFTh-C60 or Th-C60-based counterpart devices. Our results indicate that high-performance solar cells can be achieved by the morphology control of active thin films. Diarylfluorene-modified C60 derivatives are promising n-type organic semiconductors for their applications in BHJ PSCs.
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