| Designing and synthesis of organic molecules with excellent photoelectricalproperties have attracted growing attention in the development of functional materials.According to their functions, they can be classified into organic solar cells, organicfield-effect transistors, organic memory devices, organic light emitting diodes and so on.Based on our group work, I sticked to my work in the following aspects:(1) We have successfully synthesized a novel larger heteroacene, CDPzN, containingtwo different types of heteroactoms (nitrogen and oxygen atoms) in their backbones andhaving nine fused rings. The sandwich-structure memory devices based on CDPzNexhibited excellent ternary memory behavior with high ON2/ON1/OFF current ratios of106.3/104.3/1and good stability for the three states. We believe that our results couldprovide guidance for the design and synthesis of new heteroacenes, which could be used aspromising candidates in nonvolatile memory devices.(2) We have successfully designed and synthesized a novel largest heteroacenewith eleven linearly-fused rings (2,3,15,16-tetradecyloxy-5,8,10,13,18,21,23,26-octaaza-7,11,20,24-tetraoxohendecacene, abbreviated as8N8O), which is the longest one now, and found that it can act as an efficient anion sensor for iodide over a wide range of other anions (F-, Cl-, Br-, PF6-, HSO4-, NO3-, BF4-, AcO-, CN-, and H2PO4-) due to the “heavy-atom” effect. Among the range of biologically important anions, iodide plays a vital role in many biological activities such as thyroid gland function.(3) We have successfully synthesized a novel larger stable polycyclic aromaticcompound,4N4OPz, which has two different types of heteroatoms (O and N) and twodifferent types of electron-withdrawing groups (nitro and pyrazine). Thesandwich-structure memory devices based on4N4OPz exhibited excellent ternary memorybehavior with high ON2/ON1/OFF current ratios of108.7/104.2/1, low switching thresholdvoltage of-1.80V/-2.87V, suggesting that the ternary memory device has low-power consumption and is a potential candidate for low-cost and high-performance memory chipsin portable nanoelectronic devices. The low STVs of our memory device may be mainlyattributed to the formation of H-aggregation, which is favorable for carrier transport. It isworth noting that the ON2/ON1and ON1/OFF current ratios in the above device are ashigh as104, which is enough to promise a low misreading rate through the precise controlof the ON2, ON1and OFF states. This device exhibits a typical write-onceread-many-times (WORM) behaviour. The memory performance was confirmed byITO/4N4OPz/LiF/Al device. The conduction mechanism through ITO/4N4OPz/Al deviceshows multilevel memory characteristics due to the two charge traps with differentelectron-withdrawing ability of tetranitro and pyrazine. We believe that our results couldprovide guidance for the design and synthesis of new polycyclic aromatic compounds,which could be used as promising candidates in nonvolatile memory devices.(4) Two organic small molecules (ATPP and ATPP-NI) bearing a pyrazoline moietywere investigated as an electrical memory material. The sandwich-structure memorydevices based on ATPP-NI exhibited excellent volatile static random access memory(SRAM) and good stability. However, the behaviors of memory devices based on ATPPare depended on compliance currents. The as-prepared device (ATPP as an electro-activefilm) exhibited different memory behaviors from nonvolatile ‘switch-off’ to volatileSRAM through decreasing the compliance currents from0.1A to0.001A, due to therupture of the metal filaments part in the conductive pathway at the high current density ofthe ON-state.(5) An AIE-active initiator was introduced at the end of polymer chain and made theusual polymers emissive dramatically. Although the AIE effect of this small molecule isnot distinctive, the obvious amplification of polymers is observed. It should partly attributeto the wrapping and coiling of flexible hydrophobic chains. In our case, the AIE effect isoriginated from initiator TPP-NI, but amplified through polymer chains or tuned byhydrophobicity of polymer side chains. The obtained polymers exhibit not only AIE effectof end group but also the property of polymer chains such as easy fabrication. In particular,the PHEMA shows a pH-optical sensitive phenomenon which is not obvious both in smallmolecules and usual polymers without such a fluorphore. We believed such a method ispromising in preparation of AIE polymers and studying the morphology of classicalpolymers by using fluorescence. (6) We reported two pyrazoline initiators (TPP-A and TPP-NI) with different chargetransfer (CT) and aggregation fluorescence property. Four their end-functionalizedpolymers, PS-A, PS-NI, PNIPAM-A and PNIPAM-NI, were obtained using TPP-A orTPP-NI as an initiator via ATRP. TPP-A exhibits a weak CT and aggregation causedquenching, but TPP-NI possesses a strong CT and aggregation induced emission. After twoinitiators were introduced to PS chains, the CT of PS-A and PS-NI are well-preserved, buttheir PL intensity is increased because the PS chains could separate initiators fromintermolecular interactions and restrict their intramolecular rotations. However, theemission behaviours of their end-functionalized PNIPAM (PNIPAM-A and PNIPAM-NI)are different, but the emission behaviours of PNIPAM-A and PNIPAM-NI are similar totheir corresponding initiators, respectively. As a result, PNIPAM-A exhibits a weak CTand aggregation caused quenching and PNIPAM-NI exhibits a strong CT and aggregationinduced emission due to the different polarity of PNIPAM and initiators. The LCST of theaqueous PNIPAM-A and PNIPAM-NI solution were31.6and32.8°C, respectively. At40°C, polymer aqueous solution possessed higher emission intensities than thosemeasured at room temperature. In summary, we have successfully utilized the polymerchains to tune the optical properties of the luminophores, and studied the interactionbetween the polymer chains and initiators with different CT.(7) The fluorescence properties of monomer StTPP-NI and homopolymer PStTPP-NIwith pyrazoline and l,8-naphthalimide segments have been studied in various polarsolvents and in the aggregated state. In nonpolar solvents, such as cyclohexane, the PLspectra are associated with the emissions from their LE states with a high QY. In polarsolvents, such as DMF, the red-shift and weaker emission from the ICT states dominatetheir PL spectra, which indicates a transition from the LE state to the ICT state. Theaddition of large amounts of poor solvents into the solutions of the luminogens induces theStTPP-NI and PStTPP-NI to aggregate, which promotes their ICT emissions through theAIE process. The two-photon properties of StTPP-NI and PStTPP-NI were also studied.PStTPP-NI in toluene shows two-photon fluorescence with high brightness. The TPA crosssection value of polymer in toluene is983GM, which is much higher than that ofStTPP-NI in toluene (22GM), due to the steric effect of polymer chains. In the aggregatedstate, the TPA action cross section of PStTPP-NI in DMF/ethanol is4.98-fold higher than that in pure DMF. Therefore, the use of an AIE-active polymer in TPF or TPA studies maybecome a new method to obtain higher cross-section TPA materials. |
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