Flexible Alkyl Spacer Research Articles

Formation of Layered Liquid Crystal by Cooperation of Sidechain Array and Rigid Polyacetylene Mainchain

ABSTRACT An acetylene derivative monomer with a pyrimidine – type sidechain with three rings was synthesized by Steglich esterification. Polymerization of the acetylene derivative was then carried out with a rhodium complex. The acetylene monomer and mono-substituted polyacetylene derivative showed liquid crystals (LCs) because their tricyclic parts worked as a mesogenic core. The monomer as an acetylene derivative showed smectic with a tilted structure in the LC aggregation form. The mono-substituted polyacetylene bearing mesogen via short alkyl spacer showed lyotropic and thermotropic LCs of the smectic phase, although generally flexible long alkyl spacer from the main chain connected to sidechain mesogen is required for exhibiting liquid crystal in sidechain type polymer liquid crystals. In the present study, rigid mainchain aligns the sidechain mesogen array to form non-tilted LC. Properties of LCs were evaluated by various analytical techniques, including polarizing optical microscopy. Structural properties were evaluated by nuclear magnetic resonance spectroscopy, gel permeation chromatography, infrared spectroscopy, and ultraviolet – visible absorption spectroscopy.

Cycloaliphatic Quaternary Ammonium Functionalized Poly(oxindole biphenyl) Based Anion-Exchange Membranes for Water Electrolysis: Stability and Performance.

Mechanically robust anion-exchange membranes (AEMs) with high conductivity and long-term alkali resistance are needed for water electrolysis application. In this work, aryl-ether free polyaromatics containing isatin moieties were prepared via super acid-catalyzed copolymerization, followed by functionalization with alkaline stable cyclic quaternary ammonium (QA) cationic groups, to afford high performance AEMs for application in water electrolysis. The incorporation of side functional cationic groups (pyrrolidinium and piperidinium) onto a polymer backbone via a flexible alkyl spacer aimed at conductivity and alkaline stability improvement. The effect of cation structure on the properties of prepared AEMs was thoroughly studied. Pyrrolidinium- and piperidinium-based AEMs showed similar electrolyte uptakes and no obvious phase separation, as revealed by SAXS and further supported by AFM and TEM data. In addition, these AEMs displayed high conductivity values (81. 5 and 120 mS cm-1 for pyrrolidinium- and piperidinium-based AEM, respectively, at 80 °C) and excellent alkaline stability after 1 month aging in 2M KOH at 80 °C. Especially, a pyrrolidinium-based AEM membrane preserved 87% of its initial conductivity value, while at the same time retaining its flexibility and mechanical robustness after storage in alkaline media (2M KOH) for 1 month at 80 °C. Based on 1H NMR data, the conductivity loss observed after the aging test is mainly related to the piperidinium degradation that took place, probably via ring-opening Hofmann elimination, alkyl spacer scission and nucleophilic substitution reactions as well. The synthesized AEMs were also tested in an alkaline water electrolysis cell. Piperidinium-based AEM showed superior performance compared to its pyrrolidinium analogue, owing to its higher conductivity as revealed by EIS data, further confirming the ex situ conductivity measurements.

Highly stable side-chain-type cardo poly(aryl ether ketone)s membranes for vanadium flow battery

Vanadium flow batteries (VFBs) have drawn considerable attention as an emerging technology for large-scale energy storage systems (ESSs). One of the pivotal challenges is the availability of eligible ion exchange membranes (ICMs) that provide high ion selectivity, proton conductivity, and stability under rigorous condition. Herein, a ‘side-chain-type’ strategy has been employed to fabricate highly stable phenolphthalein-based cardo poly(arylene ether ketone)s (PAEKs) membrane with low area resistance (0.058 Ω cm2), in which flexible alkyl spacers effectively alleviated inductive withdrawing effect from terminal ion exchange groups thus enabling a stable backbone. The assembled VFBs based on PAEKs bearing pendent alkyl chain terminated with quaternary ammonium (Q-PPhEK) demonstrated an energy efficiency above 80% over 700 cycles at 160 mA/cm2. Such a remarkable results revealed that the side-chain-type strategy contributed to enhancing the ICMs stability in strong oxidizing environment, meanwhile, more interesting backbones would be woken with this design engaging in stable ICMs for VFBs.

Synthesis and Mesomorphic Properties of New Non-symmetric Liquid Crystal Dimers

Abstract: New non-symmetric liquid crystal dimers, N-(4-(n-(4-(benzothiazol-2-yl)phenoxy) alkyloxy) benzylidene)-2,4-difluoroaniline (DSFCn), containing two mesogenic core units of benzothiazole and benzylideneaniline were reported. The core system was connected by a flexible alkyl spacer, -(CH2)n-(where n =2-6, 8, 10, and 12). The spectroscopic techniques were employed to confirm the molecular structure of the title compounds. Differential scanning calorimetry and polarizing optical microscopy were used to study the mesomorphic properties of the synthesized compounds. Observation under crossed polarized light reveals that compounds (n = 4, 5, 6, 8, 10, 12) are purely nematogens. The nematic phase in the dimers are caused by the presence of the lateral fluorine atoms at the benzylideneaniline core. Mesophase thermal stability has been suppressed significantly by the fluorine atom at the lateral position which increased the molecular breadth and subsequently, results in weaker overall lateral intermolecular attraction. The structure-property relationships of the dimers were inferred through comparison of thermal properties of the present dimers with those of the earlier reported analogous that do not possess any lateral substituents.

Color-tunable photoluminescent discotic liquid crystal based on perylene – Pentaalkynylbenzene triad

This article describes the design and development of a discotic triad, where perylene is sandwiched between two pentaalkynyl benzene units, linked via a flexible alkyl spacer. The thermotropic liquid crystalline properties of the compound were analyzed by differential scanning calorimetry (DSC), polarising optical microscopy (POM), and wide-angle X-ray diffraction (WXRD) techniques. The compound exhibits columnar oblique (Colob) mesophase that sustains over a significant temperature range. The corresponding electron density map was derived from the intensities observed in the diffraction pattern. The photophysical behaviour of the compound in various solvents of varying polarity has been studied. The compound shows positive solvatochromism with a significant increase in Stoke's shift of around 91 nm between toluene and ethanol. The compound shows high fluorescence quantum yield in non-polar solvents and the lowest in polar solvents. The presented luminescent material with positive solvatochromism will reveal its potential application in fluorescence imaging and the field of optoelectronic organic materials.

Alkali-Stable Anion Exchange Membranes Based on Poly(xanthene).

Poly(xanthene)s (PXs) carrying trimethylammonium, methylpiperidinium, and quinuclidinium cations were synthesized and studied as a new class of anion exchange membranes (AEMs). The polymers were prepared in a superacid-mediated polyhydroxyalkylation involving 4,4'-biphenol and 1-bromo-3-(trifluoroacetylphenyl)-propane, followed by quaternization reactions with the corresponding amines. The architecture with a rigid PX backbone decorated with cations via flexible alkyl spacer chains resulted in AEMs with high ionic conductivity, thermal stability and alkali-resistance. For example, hydroxide conductivities up to 129 mS cm-1 were reached at 80 °C, and all the AEMs showed excellent alkaline stability with less than 4% ionic loss after treatment in 2 M aq. NaOH at 90 °C during 720 h. Critically, the diaryl ether links of the PX backbone remained intact after the harsh alkaline treatment, as evidenced by both 1H NMR spectroscopy and thermogravimetry. Our combined findings suggest that PX AEMs are viable materials for application in alkaline fuel cells and electrolyzers.

A molecular dyad delivered by biodegradable polymeric nanoparticles for combined PDT and NO-PDT in cancer cells

The design, synthesis, photochemical properties, and biological evaluation of a novel molecular dyad with double photodynamic action and its formulation within biodegradable polymeric nanoparticles (NPs) are reported. A BODIPY-based singlet oxygen (1O2) photosensitizer (PS) and a nitric oxide (NO) photodonor (NOPD) based on an amino-nitro-benzofurazan moiety have been covalently joined in a new molecular dyad, through a flexible alkyl spacer. Excitation of the dyad with visible light in the range 400–570 nm leads to the concomitant generation of the cytotoxic 1O2 and NO with effective quantum yields, being ΦΔ = 0.49 ± 0.05 and ΦNO = 0.18 ± 0.01, respectively. Besides, the non-fluorescent NOPD unit becomes highly fluorescent after the NO release, acting as an optical reporter for the NO photogenerated. The dyad is not soluble in water medium but can be effectively entrapped in water-dispersible, biodegradable polymeric NPs made of mPEG-PCL, ca. 66 nm in diameter. The polymeric nano-environment affects in an opposite way the photochemical performances of the dyad, reducing ΦΔ to 0.16 ± 0.02 and increasing ΦNO to 0.92 ± 0.03, respectively. The NPs effectively deliver the photoactive cargo into the cytoplasm of HepG2 hepatocellular carcinoma cells. A remarkable level of cell mortality is observed for the loaded NPs at very low concentrations of the dyad (1–5 µM) and very low light doses (≤0.8 J cm−2) more likely as the result of the combined photodynamic action of 1O2 and NO.

Quinuclidinium-piperidinium based dual hydroxide anion exchange membranes as highly conductive and stable electrolyte materials for alkaline fuel cell applications

Anion-exchange membrane fuel cells (AEMFCs) utilizing quaternary ammonium functionalized poly(arylene ether sulfone)s have been rapidly advanced in the clean energy research arena. However, it is highly desirable to integrate the benefits of quaternary ammonium cations in the polymeric membrane systems to achieve a high-power output together with substantial stabilities that significantly reduce the material costs. Herein, we report the tethering of two different quinuclidinium and piperidinium cations separated by a flexible –(CH2)4˗ spacer as a dual hydroxide conductor in the poly(arylene ether sulfone)s copolymer membrane (QP-PES) for enhancing the structural and physical properties as well as the ionic conductivities. The results proved that the tethering of dual hydroxide conductor in the PES backbone led to show maximum hydroxide conductivity of 88 mS cm−1 at 80 °C while enabling a hydrophilic/hydrophobic micro-phase separation due to the presence of flexible alkyl spacer. We also investigated the properties of a single hydroxide conductor exclusively comprising the quinuclidinium cation (Q-PES) and compared it with that of QP-PES. Interestingly, both the Q-PES and QP-PES membranes displayed superior thermal, mechanical, and dimensional stabilities. Most importantly, the QP-PES membrane demonstrated excellent alkaline stability over the period of 1000 h due to the existence of dual hydroxide conductor together with alkyl spacer units. Furthermore, the maximum power density of a H2/O2 single cell using QP-PES (92.3 mWcm−2) is higher than that of QP-PES (70.0 mWcm−2). The results provide a greater perception to design the high performance AEM materials.

Chiral molecular nanosilicas.

Molecular nanoparticles including polyoxometalates, proteins, fullerenes and polyhedral oligosiloxane (POSS) are nanosized objects with atomic precision, among which POSS derivatives are the smallest nanosilicas. Incorporation of molecular nanoparticles into chiral aggregates either by chiral matrices or self-assembly allows for the transfer of supramolecular chirality, yet the construction of intrinsic chirality with atomic precision in discrete molecules remains a great challenge. In this work, we present a molecular folding strategy to construct giant POSS molecules with inherent chirality. Ferrocenyl diamino acids are conjugated by two or four POSS segments. Hydrogen bonding-driven folding of diamino acid arms into parallel β-sheets facilitates the chirality transfer from amino acids to ferrocene and POSS respectively, disregarding the flexible alkyl spacers. Single crystal X-ray structures, density functional theory (DFT) calculations, circular dichroism and vibrational circular dichroism spectroscopy clearly verify the preferential formation of one enantiomer containing chiral molecular nanosilicas. The chiral orientation and chiroptical properties of POSS show pronounced dependence on the substituents of α-amino acids, affording an alternative way to control the folding behavior and POSS chirality in addition to the absolute configuration of amino acids. Through the kinetic nanoprecipitation protocol, one-dimensional aggregation enables chirality transfer from the molecular scale to the micrometer scale, self-assembling into helices in accordance with the packing propensity of POSS in a crystal phase. This work, by illustrating the construction of chiral molecular nanosilicas, paves a new way to obtain discrete chiral molecular nanoparticles for potential chiroptical applications.

Influence of Alkyl Chain Spacer Length on the Charge Carrier Mobility of Isotactic Poly(N-carbazolylalkyl acrylates).

In the search for semiconducting polymer alternatives to conjugated polymers, stereoregular nonconjugated pendant electroactive polymers (NCPEPs) have recently shown competitive hole mobilities with conjugated polymers and a dramatic increase in mobility relative to atactic analogues. Here we investigate one of the key structural variables of NCPEPs: the flexible alkyl spacer that separates the electroactive pendant from the backbone. We investigate a straightforward postpolymerization functionalization synthetic method to synthesize such polymers with high isotacticity using poly(N-carbazolylalkyl acrylate) as a model system, where the alkyl chain spacer in the NCPEPs is varied from 2 to 12 carbons. We observed that the hole mobility increased from the two-carbon spacer, resulting in the highest mobility upon thermal annealing with a four-carbon spacer for 75% isotactic polymers and with a six-carbon spacer for 87% isotactic polymers. As such, we have demonstrated an important role of the spacer chain in influencing mobility. For all spacer lengths, higher mobilities were measured with the more isotactic polymer. While physical characterization of the largely amorphous polymers yielded little insight into the structure-function relationships, DFT and MD simulations indicated helical structures for the polymers where intermolecular short-range π-stacking is observed and is affected by spacer chain length. This work demonstrates that both the degree of stereoregularity and the spacer chain length play a role in determining the hole mobility in NCPEPs.

Highly conductive hydroxide exchange membranes containing fluorene-units tethered with dual pairs of quaternary piperidinium cations

In the pursuit of anion exchange membranes (AEMs) with high alkaline stability and hydroxide conductivity, we have prepared and characterized a series of poly(fluorene alkylene)s in which each fluorene unit was functionalized with dual pairs of quaternary piperidinium cations on flexible alkyl spacer chains. First, ether-free precursor polymers were synthesized in superacid mediated polyhydroxyalkylations involving 2,2,2-trifluoroacetophenone, 9,9-dimethyl-2,7-diphenyl-9H-fluorene, and different amounts of 2,7-dibromo-9,9-bis(6-bromohexyl)-fluorene to regulate the degree of bromoalkylation. Subsequently, the bromoalkyl side chains were utilized to introduce bis-piperidinium (bisPip) cations via Menshutkin reactions. These materials formed transparent and mechanically strong AEMs upon casting. At 80 °C, the hydroxide conductivity of bisPip AEMs reached 85 and 150 mS cm–1 at ion-exchange capacities (IECs) of 2.0 and 2.8 mequiv g–1, respectively. Moreover, the bisPip AEMs showed high alkaline stability with an ionic loss of merely 6% following immersion in 5 M aq. NaOH solution for a period of 168 h at IEC = 2.8 mequiv g–1. Under these conditions, 1H NMR data indicated that a β-hydrogen in an alkyl spacer chain was about 8 times more susceptible to attacks by hydroxide ions than a β-hydrogen in a piperidinium ring. In comparison, corresponding AEMs with fluorene units functionalized with monoPip cations (i.e., a single pair of piperidinium cations per fluorine unit) showed lower conductivity and alkaline stability under the same conditions, demonstrating the advantage of locally concentrating the cations in the polymer structure by employing bisPip side chains.

Efficient solution-processed deep-blue CIEy ∈ (0.05) and pure-white CIEx,y ∈ (0.34, 0.32) organic light-emitting diodes: experimental and theoretical investigation

Two bipolar non-conjugated deep-blue emitters, PICFOCz and BICFOCz, were synthesized by incorporating the charge transporting carbazole (donor/hole transporting) and imidazole (acceptor/electron transporting) moieties via a flexible alkyl spacer.

VO(IV) Complexes of N2O2 Tetra Dentate Ligands With Flexible Alkyl Spacer: Synthesis, Characterization and Antibacterial Activities

1,4-diaminobutane was synthesized with 2-furan-carboxyaldehyde using Schiff base condensation method leading to a new ligand containing N2O2 donor. The same reaction path was followed replacing 1,4-diaminobutane by 1,6-diaminohexane and 1,8-diaminooctane in separate reactions to obtain the two other new ligands. Then, the synthesized ligands were employed to attain the Oxo-vanadium(IV) complexes as results of their reactions with VOSO4.H2O. The ligands were characterized by FT-IR, 13C-NMR, 1H-NMR, LC ESI/MS. The VO(IV) complexes were elucidated by FT-IR, energy dispersive x-ray spectrum (EDX), thermogravimetric (TG) methods and the conductivity and magnetic susceptibility measurements. The antibacterial activities of the ligands and their complexes were determined on the microorganisms which can be aligned as Escherichia coli ATCC 25922, Salmonella thphimurium ATCC 14028, Staphylococcus aureus ATCC 25923, Listeria monocytogenes ATCC 19115 and Bacillus cereus ATCC 11778. The complexes, in general, appeared to be more active than their parent ligands. All the activities can be classified as moderate in comparison with the corresponding antibiotic effect on the same bacteria.

Highly Conductive Nonstoichiometric Protic Poly(ionic liquid) Electrolytes

Nonstoichiometric protic ionic liquids have recently gained interest because proton acceptors are crucial in the electrolyte of many electrochemical applications such as fuel cells, proton batteries and supercapacitors. In the present work we have prepared and studied several protic poly(ionic liquid)s doped with acid in nonstoichiometric amounts. The poly(ionic liquid)s were based on polydimethylsiloxane backbones functionalized with imidazole, 1,2,4-triazole and benzimidazole groups, respectively, via flexible alkyl spacer units. These polymers did not show any observable glass transition above -50 °C, resulting in high charge mobility and conductivities of up to 19 µS/cm at 25 °C. Additional doping with free imidazole significantly increased the conductivity, to 0.15 mS/cm at 25 °C, more than four orders of magnitude higher than in the nondoped state. The origins of the fast charge transport in these polymer electrolytes were investigated by electrochemical impedance spectroscopy and electrode polarization analysis. The results indicate that these kinds of nonstoichiometric protic poly(ionic liquid)s have potential as high-performance electrolytes for room temperature electrochemical cells, such as organic proton batteries, where the availability of both proton donors and acceptors is important. (Less)

Near UV/Deep‐Blue Phenanthroimidazole‐Based Luminophores for Organic Light‐Emitting Diodes: Experimental and Theoretical Investigation

AbstractTwo new deep blue phenanthroimidazole base luminophores 2‐(4‐(4‐(4‐(1‐phenyl‐1H‐phenanthro[9,10‐d]imidazol‐2‐yl)phenoxy)butoxy)phenyl)‐1‐phenyl‐1H‐phenanthro[9,10‐d]imid –azole (DPIPOBn) and 2‐(4‐(4‐(4‐(1‐(4‐tert‐butylphenyl)‐1H‐phenanthro[9,10‐d]imidazol‐2‐yl) phenoxy)butoxy)phenyl)‐1‐(4‐tert‐butylphenyl)‐1H‐phenanthro[9,10‐d]imidazole (DPITBOBn) were designed and synthesized by linkage two phenanthroimidazole functional units via the highly flexible alkyl (butane) spacer with different N1 functional groups (benzene and tert‐butylbenzene). The synthesized luminophores were structurally characterized by spectroscopic method (1H, 13C, and mass). The photophysical, electrochemical and electroluminescence properties of the luminophores were systematically studied. These luminophores emit intense blue PL emission in both solution and solid phase. The HOMO‐LUMO energy level of the luminophores was calculated from Cyclic Voltammetry (CV) analysis and which agreed with the results from the density‐functional‐theory (DFT) calculation. The time‐dependent DFT (TD‐DFT) calculation was performed to know the excited states (singlet and triplet) of the luminophores. The solution‐processed OLED was fabricated to test these materials as emissive materials and as emitters. All the doped devices exhibited near‐UV emission with EL peaks centered around 380–395 nm with Commission International deL'Eclairage (CIE) coordinate of (0.16, 0.09 or 0.10). Among all the doped devices, DPITBOBn (3 wt%) based device displayed a power efficiency (PE) of 0.5 lm/W, a current efficiency (CE) of 1.2 cd/A and external quantum efficiency (EQE) of 1.9% at the brightness 100 cd/m2.

Synthesis of novel core-shells of PMMA with coumarin based liquid crystalline side chains and PMMA shell as electro-optical materials

The synthesis and electro-optical properties of novel side-chain liquid crystalline polymers (SCLCPs) is described. The polymers were liquid crystalline polymers with mesogenic coumarin based side groups separated from the poly (methyl methacrylate) backbone by flexible alkyl spacers of varying lengths. The effect of the flexible spacer length on the phase properties and electric field effects as well as effect of polymer structure on the electro-optical properties of liquid crystalline polymers is investigated. Considering the results of analysis such as DSC and POM, the sample with longer spacer length and more liquid crystal properties was subjected to further characterizations. The particles of sample with longer spacer was covered with a PMMA shell of different thicknesses and their electro-optical properties were studied showing an 80% of change in transmittance by change of applied potential from 0 to 14 V. To the best of our knowledge this is the first study in its kind on this type of structures.

Multiple Effects Tailoring the Self-organization Behaviors of Triphenylene Side-chain Liquid Crystalline Polymers via Changing the Spacer Length

Long-alkyl tail triphenylene (TP) side-chain liquid crystalline polymers (SCLCPs) with different spacer length (P-m-TP, m = 2, 3, 4, 6, 8, which is the number of carbon atom in the flexible alkyl spacers) have been successfully synthesized via free radical polymerization. The differential scanning calorimetry (DSC), polarized light microscopy (POM), ultraviolet-visible spectroscopy (UV-Vis), wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) measurements were performed to investigate the influence of multiple effects on the self-organization behaviors of P-m-TP, including steric effect, decoupling effect and π-π stacking effect. The experimental results revealed that P-m-TP (m = 2, 3, 4) formed the columnar phase which was developed by the TP moieties and the main chain as a whole, suggesting that the side-chains had strong steric effect even though the number of spacer length (m) exceeded 4. In addition, the clearing points (Tis) of the polymers were above 300 °C. When m = 6 and 8, the polymers displayed hexagonal columnar phase and exhibited the low Tis (91 and 80 °C respectively), originating from the self-assembly of triphenylene due to the decoupling effect and π-π stacking effect. This work offers a viable and inspiring pathway to control the phase transition temperature and phase structure of TP SCLCPs via simply tailoring the spacer length and increasing the alkyl tail length of TP.

Structure–property relationships in lath-shaped triads based on multialkynylbenzene

ABSTRACTThis report elaborates the synthesis of symmetrical triads based on multialkynylbenzene linked via flexible alkyl spacers. Four mesogens were synthesised in which multialkynylbenzene units were connected to each other in a side-by-side fashion with varying flexible alkyl spacers. The compound with longest alkyl spacer, i.e. n = 7, exhibited ND phase which has been characterised by polarised optical microscopy and detailed X-ray scattering studies (small/wide-angle X-ray scattering). Surprisingly, this triad shows ND phase at high temperature as compared to our previous reports on room-temperature ND phases.

Anion exchange membrane from polyvinyl alcohol functionalized with quaternary ammonium groups via alkyl spacers

Anion exchange membranes (AEMs) functionalized with quaternary ammonium groups are prepared from polyvinyl alcohol for alkaline polymer electrolyte fuel cell (APEFC) application. A series of AEMs were synthesized by direct quaternization of PVA using flexible alkyl spacer as charge carrier added in different weight percentages. These membranes were further cross-linked chemically and thermally before evaluating their ionic conductivity and ion exchange capacity. The interaction of alkyl spacer group with the polymer backbone was confirmed by FT-IR spectroscopy. XRD pattern reveals that the introduction of quaternary ammonium group disrupts the crystalline structure of polymer, increasing its amorphous phase thereby enhancing the conductivity. The QPVA membrane with 15 wt% of alkyl spacer exhibited an improved conductivity of 0.0057 S cm−1 at 40 °C in comparison with other ratios. The cell polarization data for the optimized QPVA membrane was studied at 40 °C with varying ionomer amount. The alkaline stability and cell durability for the optimized QPVA membrane were evaluated for 300 and 25 h, respectively.

Room-Temperature Columnar Nematic and Soft Crystalline Columnar Assemblies of a New Series of Perylene-Centred Disc Tetramers.

Three new oligomeric perylene (PE) tetraester derivatives, consisting of a PE-based core with four pentaalkynylbenzene units attached through flexible alkyl spacers, are reported. These derivatives were investigated for their mesomorphic properties and thermal, photophysical, and electrochemical behaviour. Small- (SAXS) and wide-angle X-ray scattering (WAXS) studies were performed to deduce the exact nature of the phases. To resolve overlapping reflections and facilitate their indexing, grazing-incidence SAXS/WAXS experiments were carried out on oriented thin films on indium tin oxide (ITO)-coated glass substrate. The corresponding electron density maps were derived from the intensities observed in the diffraction pattern. Whereas compounds with shorter alkyl spacers (n=6 and 8) were found to self-organise into soft crystalline columnar assemblies, those with longer spacers (n=10) exhibited a liquid-crystalline columnar nematic mesophase. This is in contrast to previous reports that describe highly symmetric 2D hexagonal and rectangular columnar structures of PE-based mesogens. The morphology of self-assembly was found to transform from soft crystal columnar to nematic columnar phase through simple variation in the number of alkyl spacers. All compounds exhibited excellent fluorescence emission properties with a very good quantum yield and large band gap. Apart from high solubility and good quantum yield, these compounds can serve as standards to measure quantum yields of unknown samples. These compounds also display green luminescence and may find applications for various optoelectronic devices.