Investigation of aggregation induced emission in 4-hydroxy-3-methoxybenzaldehyde azine and polyazine towards application in (opto) electronics: synthesis, characterization, photophysical and electrical properties

<p>An azine monomer 4-hydroxy-3-methoxybenzaldehyde azine was synthesized by refluxing with ethanolic solution of vanillin with hydrazine hydrate. It was then converted into polyazine by oxidative polymerization. The structure of azine and polyazine was characterized by FT-IR, UV–visible, ¹H-NMR and ¹³C-NMR. Spectral results suggest the formation of polymer, through C–C and C–O–C coupling of the phenylene and oxyphenylene. The relationship between the structures and photophysical properties of azine and polyazine was studied. Both azine and polyazine show, aggregation induced emission with increase in concentration in DMSO solution. The single crystal structure of azine suggesting the various inter and intra molecular interactions rigidify the conformation and locked the intramolecular rotations of the phenyl rings in the molecule. The inhibition of intramolecular rotation, J- aggregation and increase of conjugation impart the fluorescence in aggregated state. Additionally, the electronic properties namely orbital energies and resulting energy gap calculated theoretically by density functional theory (DFT).</p

Environment-dependent Emission Tuning in the Multicolor Nitrogen-doped Carbon Quantum Dots

Carbon quantum dots (CQDs) are fascinating luminous materials from the carbonaceous family and are increasingly being investigated in many optoelectronic applications due to their unique photoluminescence (PL) characteristics. Herein, we report the synthesis of nitrogen-doped carbon quantum dots (NCQDs) from citric acid and m-phenylenediamine using a one-pot hydrothermal approach. The environment-dependent emission changes of NCQDs were extensively investigated in various solvents, in solid-state, and in physically assembled PMMA-PnBA-PMMA copolymer gels in 2-ethyl hexanol. The NCQDs display bright emission in various solvents as well as in solid-state and a temperature-dependent enhanced emission in gels. In detail, these NCQDs exhibit multicolor PL emission across the visible region and its enhancement upon changing the environment (solutions and polymer matrices). The NCQDs also exhibit excitation-dependent PL and solvatochromism, which are rarely observed in CQDs. Most CQDs are non-emissive in the aggregated or solid-state due to the aggregation-caused quenching (ACQ) effect, limiting their solid-state applications. However, these NCQDs display a strong solid-state emission centered at 568 nm ascribed to the presence of abundant surface functional groups, which helps to prevent the - interaction between the NCQDs and to overcome the ACQ effect in the solid-state. Interestingly, the NCQD containing gels display a significant fluorescence enhancement than the NCQDs in 2-ethyl hexanol solution because of the interaction between the polar PMMA blocks and NCQDs. This research opens up the development of large-scale, low-cost multicolor phosphor for the fabrication of optoelectronic devices, sensing, and bioimaging applications

Achieving Single-Component Solid-State White-Light Emission through Polymerization-Induced Phosphorescent Emission

The non-luminescent monomeric unit M1 transforms into intensely yellow emissive phosphorescent polymers upon polymerization, termed polymerization-induced phosphorescent emission (PIPE). A simple free radical polymerization method is employed for the polymer synthesis where the homopolymer (HP) exhibiting PIPE is generated from vinyl monomers (M1) via non-conjugated bond formation. High photo efficiency observed for the PIPE-active HP may have resulted from the possible intrachain and interchain interactions, among the repeating units. By using various monomer compositions, this synthetic technique provides copolymer and emission tuning. Integrating blue-emitting carbazole with the PIPE-active HP resulted in the white-light-emitting copolymer (CP4). This is the first report on PIPE-active-mediated white-light-emitting copolymer with CIE coordinates (0.25, 0.33). The resulting copolymer (CP4) showed a high quantum yield (33.7%) with a long excited-state lifetime (6.54 μs). PIPE-active phosphorescent-based white-light-emissive polymeric materials could motivate the development of advanced materials for white-light-emitting diode devices

Nanoscale Self-Assembly of Poly(3-hexylthiophene) Assisted by a Low-Molecular-Weight Gelator toward Large-Scale Fabrication of Electrically Conductive Networks

Achieving self-assembly of conjugated polymers is necessary to harness their charge transport properties in various applications, including field-effect transistors, sensors, and conductive gels for biomedical applications. Although many processes have been investigated, there are still opportunities for developing new strategies that can lead to materials with improved performances. Particularly, large-scale fabrication of three-dimensional conductive networks formed by the self-assembly of conjugated polymers and low-molecular-weight gelators (LMWGs), but with conjugated polymers at much lower quantity, would be advantageous. LMWGs can be selected from an extensive library of available systems and can be directed to self-assemble in various conditions. However, the simultaneous self-assembly of LWMGs and conjugated polymers is not fully understood. Here, we report a simple pathway for the self-assembly of poly(3-hexylthiophene) (P3HT), a conjugated polymer, in chloroform in the presence of di-Fmoc-l-lysine, an LMWG. Di-Fmoc-l-lysine was selected as the LMWG because it does not have significant interactions with P3HT. P3HT and di-Fmoc-l-lysine in chloroform form gels with decreasing temperature. UV-vis spectroscopy provides an insight into the photophysical response of the gelation process, revealing the self-assembly of P3HT in the gel network. The scattering experiments further capture the self-assembly of the P3HT network. The nanofibrillar microstructure has been captured using atomic force microscopy (AFM) for the gels without and with P3HT, where both P3HT and di-Fmoc-l-lysine form nanofibers independently. Both these nanofibers coexist and intermingle, displaying conductive domains in the dried films captured by conductive AFM. The conductive nanofibers form a percolated network in the dried samples, leading to bulk electrical conductivity similar to that of pristine P3HT films. This is achieved with only 20% P3HT content and the balance insulating di-Fmoc-l-lysine molecules. Our results provide a fundamental understanding of the self-assembly of P3HT in the presence of an LMWG, resulting in a conductive nanofibrillar network. Such knowledge can readily be implemented in other conjugated polymeric systems. The approach presented here has potential applications towards fabricating conductive gels for biomedical and sensor applications and large-scale processing of thin films for optoelectronic applications