Transient photocurrents in a charge transfer complex of trinitrofluorenone with a carbazole substituted discotic liquid crystal

Experimental and Computational studies on Intramolecular charge transfer, Terahertz and Two photon absorption of 3-[(4-Nitrophenyl Azo)]-9H-Carbazole-9-Ethanol (NPACE) from their Vibrational spectra for Optical limiting and NLO applications

Non-linear optical (NLO) features of 3-[(4-Nitrophenyl Azo)]-9H-Carbazole-9-Ethanol (NPACE) chromophore were investigated by FT-IR, FT-Raman, and UV-visible spectra aided by Density Functional Theory (DFT) using the B3LYP/6-311++G(d,p) basis set of Gaussian 16 W package. It is observed from the DFT calculation that the slight increase in the endocyclic angle of C13 -C14 -C15 and the reduction in exocyclic angle of N40 -N39 -C14 and C15 -C14 -N39 ascertained by experimental XRD values indicating the intramolecular charge-transfer interaction between the carbazole and nitrophenyl group through the diazo bridge. The vibrational contribution to the linear electro-optic effect is 15% of the total hyperpolarizability being calculated at B3LYP/6-311++G (d, p) for the NPACE molecule. It is also observed that the 8a, 19a, and 19b modes of the carbazole ring and the 8a, 8b, and 19b modes of the phenyl ring are found to be simultaneously and intensely active in IR and Raman spectra explaining the charge transfer interactions throughout the molecule. The low value of the HOMO- LUMO energy gap (2.5843 eV) and the deviation between the measured absorption wavelength (3.36 eV) from the computed (3.87 eV), both these facts substantiate the intramolecular charge transfer. The polarizability and first-order hyperpolarizability were calculated as 6.48 × 10-24 and 3.8 × 10-29 esu, respectively. The second harmonic generation (SHG) measurement experiment of NPACE was carried out using the powder method. The SHG efficiency is measured in comparison with the urea standard. The calculated torsional mode at 20 cm-1 is in excellent quantitative agreement with the experimentally determined terahertz absorption peak. The two-photon absorption coefficient of NPACE was estimated to be 0.9 × 10-11 mW-1, which is mainly due to the D-π-A type of molecular structure, and the optical limiting threshold for NPACE was estimated to be 1.52 × 1013 Wm-2 enabling this material as a potential candidate for optical limiting applications.

Charge transport in phenazine-fused triphenylene discotic mesogens doped with CdS nanowires

We report the synthesis of oleylamine capped CdS nanowires and we have dispersed a small optimized amount of these NWs in the Col_h phase of a recently synthesized phenazine-fused-triphenylene discotic liquid crystal to understand the temperature-dependent charge transport.

TNF Induced Switching of Columnar Rectangular to Hexagonal Assemblies in a New Class of Triphenylene-Based Room Temperature Discotic Liquid Crystals

A straightforward synthesis of triphenylene-based oligomeric systems that self-organize into room temperature columnar structures is presented. The compounds with longer spacer length (m = 10 and 12) exhibit columnar rectangular (Col_r) mesophase whereas the compound with m = 8 exists in glassy Col_r state. Interestingly, the Col_r self-assembly of these compounds switches to columnar hexagonal (Col_h) on doping the compounds with 2,4,7-trinitrofluorenone (TNF). For the dopant concentration of 1:1 with respect to native compound, an intermediate transition state between Col_r and Col_h phase was observed which completely transformed into the hexagonal phase on increasing the concentration to 1:2 (compound: TNF) and afterward. Both the Col_r and Col_h self-assemblies have been well resolved by detailed X-ray analysis. These kind of oligomeric compounds generally possess a combination of desirable alignment properties analogous to monomeric compounds and long-lived glassy states similar to that of polymeric mesogens. In addition, charge hopping behavior is expected to increase in these compounds due to donor-acceptor interactions. Overall, these compounds can find possible potential applications in semiconductor devices.

Experimental and DFT studies on the vibrational and electronic spectra of 9-p-tolyl-9H-carbazole-3-carbaldehyde

The compound 9-p-tolyl-9H-carbazole-3-carbaldehyde (HCCD) was synthesized and characterized by X-ray diffraction, FT-IR, FT-Raman and UV-Vis spectra. The X-ray diffraction study showed that HCCD has a Z-configuration. The benzene ring including methyl is twisted from the mean plane of the carbazole group by 59.7(3)°, which is comparable with the calculated result 65° for B3LYP/6-311++G(d, p) method. Vibrational spectra and electronic spectra measurements were made for the compound. Optimized geometrical structure and harmonic vibrational frequencies were computed with B-based DFT (BLYP, B3LYP and cam-B3LYP) methods, and WB-based DFT (WB97, WB97X and WB97XD) methods and ab initio RHF method using 6-311++G(d, p) basis set. Assignments of the observed spectra were proposed. The equilibrium geometries computed by all of the methods were compared with X-ray diffraction results. The absorption spectra of the title compound were computed both in gas phase and in DMF solution using TD-(cam)B3LYP/6-311++G(d, p) and PCM-(cam)B3LYP/6-311++G(d, p) approaches, respectively. The calculated results provide good descriptions of the bands maxima in the observed electronic spectrum. Temperature dependence of thermodynamic parameters in the range of 100-1000 K was determined. The natural atomic hybrids were calculated and discussed.

Optoelectronic Switches Based on Wide Band Gap Semiconductors

Switching of photocurrent direction in semiconducting systems upon changes of the electrode potential or incident light wavelength was realized by a series of photoelectrodes covered with titania modified with pentacyanoferrate complexes, [Fe(CN)(5)L](n)(-) (L = NH(3), thiodiethanol, thiodipropanol). These materials were characterized by optical spectroscopy and electrochemistry. The structure of the surface complexes was modeled using simple quantum-chemical models. The electrodes described in this paper enable control of the photocurrent direction by two stimuli: Changing the wavelength or the photoelectrode potential easily switches the direction of photocurrent. The materials are different from those of similar characteristics studied by other authors: They are not composites comprising of two types of semiconductors but rather engineered uniform materials. The photocurrent switching phenomenon is an intrinsic feature resulting from a specific electronic structure of the surface-modified semiconductor.

Electroactive C3symmetric discotic liquid-crystalline triindoles

Discotic liquid crystals based on triindole, a novel redox active central core, have been synthesized and their mesomorphic behaviour investigated.