Fluorescent Ferroelectrics of Hydrogen-Bonded Pyrene Derivatives

Abstract

Organic materials with diverse molecular designs show multifunctional properties such as coupled ferroelectric, optical, ferromagnetic, and transport properties. We report the design of an alkylamide-substituted pyrene derivative displaying fluorescent ferroelectric properties coupled with electron transport properties. In solution phase, this compound displayed concentration-dependent fluorescence, whereas in xerogels, a fluorescent green organogel (>0.1 mM) and entangled nanofibers were observed. A discotic hexagonal columnar liquid crystalline phase was observed above 295 K due to intermolecular hydrogen bonding and π-stacking interactions. The direction of the hydrogen-bonded chains could be inverted by the application of an external electric field along the π-stacked column, resulting in ferroelectric polarization-electric field (P-E) hysteresis. The local electric field arising from the ferroelectric macrodipole moment arrangement along the π-stacking direction affected the electron transport properties on the π-stack of pyrenes, thus confirming the current-switching phenomena according to P-E hysteresis. We report that multifunctional properties such as ferroelectricity, fluorescence, and electron transport switching were successfully achieved in hydrogen-bonded dynamic π-molecular assemblies.

Dipole‐Switchable Poly(para‐phenyleneethynylene)s: Ferroelectric Conjugated Polymers

“…[30] Thestructural investigation and the electrical behavior of the FF-HPPE suggest aferroelectric phase ( Figure 5). Ther emanent polarization was determined to be 0.45 mCcm À2 .T his matches the result of DFT calculations,in which avalue of 1.6 mCcm À2 was found, in particular when we take into account that the dipolar units will not align perfectly in the solid state.T he remanent polarization of 0.45 mCcm À2 and the coercive electric field of 5.3 V mm À1 compare well to that of other organic ferroelectric materials, [8,9,14] although the response time is relatively slow (10 À2 -10 À3 Hz), related to the stacking distance.The ferroelectric property is mirrored in the electric field dependence of the permittivity (Figure 5c), in which the typical butterfly hysteresis was observed (Figure S9). While no polarization hysteresis was found for HH-, FH-, or HPPE derivatives ( Figure S6) such hysteretic P-E characteristics were observed for FF-HPPE when the applied voltage exceeded AE 5Vmm À1 .A tAE 20 V mm À1 ,t his behavior was much more significant and remanent polarization (P r )ofcirca 0.3 mCcm À2 was observed (Figure 5a).…”

“…[31] Theobserved ferroelectric behavior relates to the dipolar moiety and the clamping of dipoles by the packing of neighboring PPE chains.T he molecular structure of PPE is vitally important for the ferroelectric behavior but provides at the same time semiconducting properties.P PEs have been employed as active layers in organic devices. [8] Current modulation in as imple memory device (Figure 6b) was demonstrated but is limited since the on/off ratio is only an order of magnitude.N onetheless,t he result suggests ferroelectric conjugated polymers could be useful for memory OLED, [6] memory OFET, [5] or high performance OPV. Fora ll PPEs,t ypical absorption and emission spectra were found.…”

“…[1,2] After removal of the applied electric field, the polarization persists and ah ysteresis is observed. [5][6][7] There are different mechanisms for organic ferroelectric effects that include hydrogen bonding, [8][9][10] liquid crystalline ordering, [11] charge-transfer complexes, [12,13] and molecular rotation. [5][6][7] There are different mechanisms for organic ferroelectric effects that include hydrogen bonding, [8][9][10] liquid crystalline ordering, [11] charge-transfer complexes, [12,13] and molecular rotation.…”

C3 Symmetric Hexaphenyltriphenylenehexamide: Molecular Design of Fluorescent Ferroelectrics

“…If we consider the high degree of freedom in molecular design and assembly, it should be possible to fabricate multifunctional organic materials that exhibit various properties, such as ferroelectric, optical and transport properties. Multifunctional ferroelectric organic materials, could lead new class of flexible organic devices.…”

“…Collective rotation of amide groups in the molecular assembly enabled the appearance of ferroelectric polarization – electric field ( P ‐ E ) hysteresis in 2BC and 3BC (Figure ) ,. Based on this result, we designed pyrenetetraalkylamide 4PC (Figure ) as a ferroelectric LC material that exhibits fluorescent properties . To extend its potential, guidelines for the design of multifunctional ferroelectric materials based on areneoligoxamide are needed.…”