Organic dyes containing indolo[2,3-b]quinoxaline as a donor: synthesis, optical and photovoltaic properties

Governing the emissive properties of 4-aminobiphenyl-2-pyrimidine push-pull systems via the restricted torsion of N,N-disubstituted amino groups

Donor-acceptor-substituted biphenyl derivatives are particularly interesting model compounds, which exhibit intramolecular charge transfer because of the extent of charge transfer between both substituents. The connection of a 4-[1,1'-biphenyl]-4-yl-2-pyrimidinyl) moiety to differently disubstituted amino groups at the biphenyl terminal can offer push-pull compounds with distinctive photophysical properties. Herein, we report a comprehensive study of the influence of the torsion angle of the disubstituted amino group on the emissive properties of two pull-push systems: 4-[4-(4-N,N-dimethylaminophenyl)phenyl]-2,6-diphenylpyrimidine (D1) and 4-[4-(4-N,N-diphenylaminophenyl)phenyl]-2,6-diphenylpyrimidine (D2). The torsion angle of the disubstituted amino group, either N,N-dimethyl-amine or N,N-diphenyl-amine, at the biphenyl end governs their emissive properties. A drastic fluorescence quenching occurs in D1 as the solvent polarity increases, whereas D2 maintains its emission independently of the solvent polarity. Theoretical calculations on D1 support the presence of a twisted geometry for the lowest energy, charge-transfer excited state (S1,90), which corresponds to the minimum energy structure in polar solvents and presents a small energy barrier to move from the excited to the ground state, thereby favoring the non-radiative pathway and reducing the fluorescence efficiency. In contrast, this twisted structure is absent in D2 due to the steric hindrance of the phenyl groups attached to the amine group, making the non-radiative decay less favorable. Our findings provide insights into the crucial role of the substituent in the donor moiety of donor-acceptor systems on both the singlet excited state and the intramolecular charge-transfer process.

Computational study of linear carbon chain based organic dyes for dye sensitized solar cells

Spectroscopic, electronic and electron injection properties of a new class of linear carbon chain (LCC) based organic dyes have been investigated, by means of density functional theory (DFT) and time-dependent density functional theory (TDDFT), for application in dye-sensitized solar cells (DSSCs). The photophysical properties of LCC-based dyes are tuned by changing the length of the linear carbon chain; UV/VIS absorption is red-shifted with increasing LCC length whereas oscillator strength and electron injection properties are reduced. Excellent nonlinear optical properties are predicted in particular for PY-N4 and PY-S4 dyes in the planar conformation. Results indicate that a LCC-bridge produces better results compared to benzene and thiophene bridges. Simulations of I--Dye@(TiO2)14 and Dye@(TiO2)14 anatase complexes indicate that designed dyes inject electrons efficiently into the TiO2 surface and can be regenerated by electron transfer from the electrolyte. Superior properties in terms of efficiency are shown by compounds with a pyrrole ring as the donor group and PY-3N is expected to be a promising candidate for applications, however all the investigated dyes could provide a good performance in solar energy conversion. Our study demonstrates that computational design can provide a significant contribution to experimental work; we expect this study will contribute to future developments to identify new and highly efficient sensitizers.

Designing of gigantic first-order hyperpolarizability molecules via joining the promising organic fragments: a DFT study

A suitable substitution of carbazole with a π-spacer group like cyanoethynylethene offers exciting future opportunities in terms of smart nonlinear optical material. In the quest of better organic nonlinear optical material, we have designed a series of derivatives based on carbazole and cyanoethynylethene fragment combinations in a unique fashion by employing the density functional (DFT) methods. The calculated time-dependent density functional theory (TD-DFT) calculations infer that the gigantic first static hyperpolarizability (β_tot) values are due to a lower energy gap and higher transition dipole moment for the crucial electronic transition. Furthermore, to see the in-depth execution for enhanced second-order nonlinear optics and the structure property relationship on nonlinear optics (NLO) behavior, we have performed frontier molecular orbitals (FMO), density of state (DOS), and transition density matrix (TDM). Furthermore, CAM-B3LYP functional-based calculated results infer that the designed molecule 10 show the first static hyperpolarizability is 923.93 × 10^-30 esu which is 69 times larger than that of p-nitroaniline.

Synthesis of a Low-Cost Thiophene-Indoloquinoxaline Polymer Donor and Its Application to Polymer Solar Cells

A simple wide-bandgap conjugated polymer based on indoloquinoxaline unit (PIQ) has been newly designed and synthesized via cheap and commercially available starting materials. The basic physicochemical properties of the PIQ have been investigated. PIQ possesses a broad and strong absorption band in the wavelength range of 400~660 nm with a bandgap of 1.80 eV and lower-lying highest occupied molecular orbital energy level of −5.58 eV. Polymer solar cells based on PIQ and popular acceptor Y6 blend display a preliminarily optimized power conversion efficiency of 6.4%. The results demonstrate indoloquinoxaline is a promising building unit for designing polymer donor materials for polymer solar cells.

Mo-Catalyzed One-Pot Synthesis of N-Polyheterocycles from Nitroarenes and Glycols with Recycling of the Waste Reduction Byproduct. Substituent-Tuned Photophysical Properties

A catalytic domino reduction-imine formation-intramolecular cyclization-oxidation for the general synthesis of a wide variety of biologically relevant N-polyheterocycles, such as quinoxaline- and quinoline-fused derivatives, and phenanthridines, is reported. A simple, easily available, and environmentally friendly dioxomolybdenum(VI) complex has proven to be a highly efficient and versatile catalyst for transforming a broad range of starting nitroarenes involving several redox processes. Not only is this a sustainable, step-economical as well as air- and moisture-tolerant method, but also it is worth highlighting that the waste byproduct generated in the first step of the sequence is recycled and incorporated in the final target molecule, improving the overall synthetic efficiency. Moreover, selected indoloquinoxalines have been photophysically characterized in cyclohexane and toluene with exceptional fluorescence quantum yields above 0.7 for the alkyl derivatives.

Efficient synthetic access to novel indolo[2,3-b]quinoxaline-based heterocycles

BACKGROUND

This paper showed the synthetic capability of the indolo[2,3-b]quinoxaline nucleus to be provided as an excellent precursor for the synthesis of various heterocyclic compounds. These synthetic routes proceed via the formation of 3-(6H-indolo[2,3-b]quinoxalin-6-yl)propane hydrazide (2). The carbohydrazide 2 and its reactions with different reagents give five and six-membered rings, such as 1,3,4-thiadiazole, 1,3,4-oxadiazole, 1,2,4-triazole, and 1,2,4-triazine.

METHODS

All chemicals used in the current study were of analytical grade. Melting points were determined using an APP Digital ST 15 melting point apparatus and were uncorrected. FT-IR spectra were recorded on a Pye-Unicam SP3-100 and Shimadzu-408 spectrophotometers in KBr pellets and given in (cm-1) KBr. The NMR spectra were detected by a Bruker AV-400 spectrometer (400 MHz for 1H, 100 MHz for 13C and 40.55 MHz for 15N), Institute of Organic Chemistry, Karlsruhe, Germany. Chemical shifts were expressed as δ (ppm) with TMS as an internal reference. Mass spectrometry was provided on a Varian MAT 312 instrument in EI mode (70 eV).

RESULTS

The target compounds were obtained, and their structures were completely elucidated by various spectral and elemental analyses (Ft-IR, 1H-NMR, 13C-NMR, and mass spectrometry).

CONCLUSION

The current work showed a view of the reactivity of the carbohydrazide group. The carbohydrazide 2 was obtained from the hydrazinolysis of carboethoxy compound 1 and exploited as a key intermediate to synthesize heterocyclic compounds with different rings.

Synthesis, Characterization, Solution Behavior and Theoretical Studies of Pd(II) Allyl Complexes with 2-Phenyl-3H-indoles as Ligands

The study of the reactivity of three 2-phenyl-3H-indole ligands of general formulae C8H3N-2-(C6H4-4-R1)-3-NOMe-5-R2 (1) [with R1 = H, R2 = OMe (a); R1 = R2 = H (b) or R1 = Cl, R2 = H (c)] with [Pd(η3-1-R3C3H4)(μ-Cl)]2 (R3 = H or Ph) has allowed us to isolate two sets of new Pd(II)-allyl complexes of general formulae [Pd(η3-1-R3C3H4)(1)Cl] {R3 = H (2) or Ph (3)}. Compounds 2a–2c and 3a–3c were characterized by elemental analyses, mass spectrometry and IR spectroscopy. The crystal structures of 2a, 3a and 3b were also determined by X-ray diffraction. 1H-NMR studies reveal the coexistence of two (for 2a–2c) or three (for 3a–3c) isomeric forms in CD2Cl2 solutions at 182 K. Additional studies on the catalytic activity of mixtures containing [Pd(η3-C3H5)(μ-Cl)]2 and the parent ligand (1a–1c) in the allylic alkylation of (E)-3-phenyl-2-propenyl (cinnamyl) acetate with sodium diethyl 2-methylmalonate as well as the stoichiometric reaction between compounds 3a and 3c with the nucleophile reveal that in both cases the formation of the linear trans- derivative is strongly preferred over the branched product. Computational studies at a DFT level on compound 3a allowed us to compare the relative stability of their isomeric forms present in solution and to explain the regioselectivity of the catalytic and stoichiometric processes.

Impact of the donor substituent on the optoelectrochemical properties of 6H-indolo[2,3-b]quinoxaline amine derivatives

An opto-electrochemical study of D–A based indolo-quinoxaline amine derivatives was performed by varying the strength of the amine substituent.

Simple diphenylamine based D–π–A type sensitizers/co-sensitizers for DSSCs: a comprehensive study on the impact of anchoring groups

Three new diphenylamine based metal-free dyes were designed and developed as efficient sensitizers as well as co-sensitizers along with N3 in DSSCs. Their detailed photophysical, electrochemical, theoretical and photovoltaic properties have been explored.

C-H Direct Arylated 6H-Indolo[2,3-b]quinoxaline Derivative as a Thickness-Dependent Hole-Injection Layer

A novel perfluoro-1,4-phenylenyl 6H-indolo[2,3-b]quinoxaline derivative (TFBIQ) was designed and synthesized by using a C-H direct arylation method. The optoelectrical properties of the obtained TFBIQ were fully characterized by UV/Vis spectroscopy, photoluminescence spectroscopy, cyclic voltammetry, and a group of Alq₃ -based green organic light-emitting diodes (OLEDs). Device A, which used 0.5 nm-thick TFBIQ as the interfacial modification layer, exhibited the five best advantages of device performance including a minimum turn-on voltage as low as 3.1 V, a maximum luminescence intensity as high as 26564 cd m^-2 , a highest current density value of 348.9 mA cm^-2 at a voltage of 11 V, the smallest efficiency roll-off, as well as the greatest power efficiency of 1.46 lm W^-1 relative to all of the other tested devices with thicker TFBIQ and also 10 nm-thick MoO₃ as hole-injection layers (HILs). As a promising candidate for an organic HIL material, the as-prepared TFBIQ exhibited a strong thickness effect on the performance of corresponding OLEDs. Furthermore, the theoretical calculated vertical ionization potential of the fluorinated TFBIQ suggests better anti-oxidation stability than that of the non-fluorinated structure.

Theoretical study of acene-bridged dyes for dye-sensitized solar cells

The electronic structures and absorption spectra for a series of acene-based organic dyes and the adsorption energy and optical properties for these dyes adsorbed on (TiO2)38 have been investigated using density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods. The effects of acene units and different substitution positions of electron donors on the optoelectronic properties of the acene-modified dyes are demonstrated. The photophysical properties of tetracene- and pentacene-based dyes are found to be tuned by changing the size of acene and the substitution position of the donor. The donor sites have a significant influence on the absorption wavelength mainly because of different molecular orbital (MO) contributions of the highest occupied molecular orbital (HOMO) on the bridging acene units, and the increasing MO contribution would lead to the red shift in the absorption spectra. Meanwhile, the donor is located close to the center of the π-conjugated bridge, and the absorption spectra are extended. The adsorption energy and optical properties of tetracene- and pentacene-based dyes adsorbed on (TiO2)38 suggest that acene-bridged dyes could be adsorbed on the TiO2 surface and inject electrons into semiconductors effectively. Then the results obtained from the hexacene-based dyes confirm the conclusions proposed from the tetracene- and pentence-based dyes. This study will provide a useful reference to the future design and optimization of acene dyes for dye-sensitized solar cell applications.

Functional tuning of organic dyes containing 2,7-carbazole and other electron-rich segments in the conjugation pathway

Organic dyes containing a triarylamine donor, a cyanoacrylic acid acceptor and a conjugation pathway composed of 2,7-carbazole, thiophene and fluorene have been synthesized and characterized as sensitizers for TiO₂-based dye-sensitized solar cells.