A novel light-emitting hydrogen-bonded (H-) acceptor PBB (M1) containing three conjugated aromatic rings, including one pyridyl terminus and two lateral methoxyl groups (on the middle ring), was successfully synthesized via Horner-Wadsworth-Emmons (HWE) olefination and Sonogashira coupling reaction. Moreover, different molar ratios of light-emitting H-acceptor monomer PBB (M1) and hole-transporting monomer CAZ (M2) bearing a carbazole unit were copolymerized through free radical polymerization to obtain lightemitting and hole-transporting H-acceptor copolymers (P1-P5). H-acceptor copolymers P3 and P4 were complexed with different generations of dendritic H-donors (G1COOH-G3COOH) bearing 1,3,4-oxadiazole (OXD) dendrons and terminal benzoic acids via H-bonded self-assembly to form supramolecular side-chain copolymers (i.e., H-bonded dendritic complexes). In contrast to H-acceptor homopolymer P1 (HPBB), H-acceptor copolymers P2-P4 incorporated with carbazole (CAZ) moieties effectively enhance the glass transition temperatures (T g s) and minimize the interchain interations of the light-emitting H-acceptor units, and similar effects occur in their H-bonded dendritic complexes. In addition, red shifts of photoluminescence (PL) emissions in H-bonded dendritic complexes can be tuned up to 61 nm. Furthermore, H-bonded dendritic complexes excited at 305 nm of OXD absorption can create a stronger fluorescence than that excited at 397 nm of PBB absorption, indicating that the intensity of the sensitized emission of PBB (by energy transfer from OXD absorption at 305 nm) is even stronger than that of a direct emission of PBB (by merely PBB absorption at 397 nm). The OXD dendritic wedges in H-bonded dendritic complexes can lower the LUMO energy levels and provide a better electron injection property. H-acceptor polymer P4 and its H-bonded dendritic complexes showed electroluminescence (EL) emissions in the range of 464-519 nm from blue to green. In addition, a PLED device containing H-bonded dendritic complex P4/G1COOH showed an EL emission of 519 nm under a turn-on voltage of 6.5 V, with a maximum luminance of 408 cd/m 2 at 18 V and a luminance efficiency of 0.39 cd/A at 100 mA/cm 2 , respectively.
Several series of novel banana-shaped H-bonded symmetric trimers (with two H-bonds) and asymmetric heterodimers (with one H-bond) were self-assembled by appropriate molar ratios of proton donors (H-donors) and acceptors (H-acceptors). The influences of H-bonded linking positions and aromatic ring numbers (4-8 aromatic rings in the rigid cores) as well as the chain lengths (n, m = 12 or 16, respectively, in the flexible parts) on the mesomorphism and the switching behavior of the bent-core supramolecules were evaluated and theoretically analyzed. Except for the supramolecular structures with longer rigid cores or shorter flexible chains possessing the rectangular columnar (Col(r) or B1) phase, the SmC(A)P(A) phase was revealed in most supramolecular asymmetric heterodimers and switched to the SmC(S)P(F) phase by applying electric fields. The polar smectic C phase was dominated for those with H-bonded sites apart from the core center. Interestingly, the SmA and nematic phases were observed in H-bonded asymmetric dimers with H-bonded sites close to the core center, which theoretically proved that the polar smectic C phase was disfavored due to an unfavorable bend angle (smaller than the lower limit of 110 degrees ) in the lowest-energy H-bonded conformer. Compared with the fully covalently bonded analogue, lower transition temperatures and lower threshold voltages were developed in the H-bonded asymmetric dimers with the polar smectic C phase. On the basis of the theoretical calculations of molecular modeling, the existence of polar switching behavior in the polar smectic C phase of asymmetric heterodimers was proven to be associated with their configurations with higher dipole moments and suitable bend angles. Furthermore, the lack of polar switching behavior in supramolecular symmetric trimers, which exhibited the regular SmC phase with weak electrical stabilities, was related to their configurations with smaller dipole moments and confirmed by theoretical calculations.
A novel light-emitting monomer M1 and its side-chain polymer P1 containing three conjugated aromatic pendants, including one pyridyl terminus, were successfully synthesized via Wittig and Pd-catalyzed Heck coupling reactions. The fluorescence of polymer P1 was efficiently quenched upon addition of different metal ions due to the facile energy transfers from the pendent groups of polymer P1 to specific metal ions. Among these metal ions, P1 exhibited extraordinary sensory selectivities for Ni(2+) and Cu(2+) ions over the other metal ions due to the stronger binding capabilities of Ni(2+) and Cu(2+) ions with polymer P1. From the time-resolved fluorescence (TRF) signals in photoluminescence spectra, the emergences of τ(1) decay components in polymer complexes (P1+Ni(2+)) and (P1+Cu(2+)) clearly indicated that their TRF traces consisted of two contributions, one from the complexes (τ(1)) and the other from free polymer P1 (τ(2)). Upon addition of Ni(2+) and Cu(2+) ions, polymer P1 showed faster decay time constants (τ(1)) of metal ion quenching on TRF signals (i.e., better quenching efficiencies on photoluminescence) than its monomer M1. Furthermore, the on-off-on fluorescent switching behavior by adding a tridentate ligand 1,1,4,7,7-pentamethyldiethylenetriamine (PMDTA) to the polymer complex (P1+Cu(2+)) for several successive cycles demonstrated a superior reusable chemosensor of P1 for further applications.
Novel supramolecular side-chain polymers were constructed by complexation of proton acceptor (H-acceptor) polymers, i.e., side-chain conjugated polymers P1-P2 containing pyridyl pendants, with low-band-gap proton donor (H-donor) dyes S1-S4 (bearing terminal cyanoacrylic acids) in a proper molar ratio. Besides unique mesomorphic properties confirmed by DSC and XRD results, the H-bonds of supramolecular side-chain structures formed by pyridyl H-acceptors and cyanoacrylic acid H-donors were also confirmed by FTIR measurements. H-donor dyes S1-S4 in solid films exhibited broad absorption peaks located in the range of 471-490 nm with optical band-gaps of 1.99-2.14 eV. Furthermore, H-bonded polymer complexes P1/S1-P1/ S4 and P2/S1-P2/S4 exhibited broad absorption peaks in the range of 440-462 nm with optical band-gaps of 2.11-2.25 eV. Under 100 mW/cm 2 of AM 1.5 white-light illumination, the bulk heterojunction polymer solar cell (PSC) devices containing an active layer of H-bonded polymer complexes P1/S1-P1/S4 and P2/S1-P2/S4 (as electron donors) mixed with [6,6]-phenyl C 61 butyric acid methyl ester (i.e., PCBM, as an electron acceptor) in the weight ratio of 1:1 were investigated. The PSC device containing H-bonded polymer complex P1/S3 mixed with PCBM (1:1 w/w) gave the best preliminary result with an overall power conversion efficiency (PCE) of 0.50%, a short-circuit current of 3.17 mA/cm 2 , an open-circuit voltage of 0.47 V, and a fill factor of 34%. V
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