Carbazole Dyes Research Articles

TD-DFT and DFT Investigation on Electrons Transporting Efficiency of 2-Cyano-2-Pyran-4-Ylidene-Acetic Acid and 2-Cyanoprop-2-Enoic Acid as Acceptors for Thiophene-Based π-Linkers Dye-Sensitized Solar Cells

Great attention is being shifted to Dye-sensitized solar cells because of their structural and electronic tunability, high performance, and low cost compared to conservative photovoltaic devices. In this work, B3LYP/6-31G** level of theory was used to study the molecular architecture of the donor-π-acceptor (D-π-A) type. This architecture contains a series of dyes with the 2-cyano-2-pyran-4-ylidene-acetic acid (PLTP-dye) and 2-cyanoprop-2-enoic acid (CLTP-dye) units as acceptors; donor groups and thiophene-based π-linkers. The molecular and electronic properties, light harvesting efficiency, open circuit voltage (VOC), injection force (ΔGinject), regeneration force (ΔGregen) and excitation state lifetime (𝜏𝑒𝑠𝑙 ) were calculated. CLTP-dyes showed lower band gap, chemical hardness (η), chemical potential (μ), higher electrophilicity (ω) and electron denoting power (ω-) than the corresponding PLTP-dyes. The ω- demonstrated that PLTP-1, PLTP-2 and PLTP-3, CLTP-1, CLTP-2 and CLTP-3 should readily push electrons to the π-linker, which can lead to high intra-molecular charge transfer and photocurrent for the dyes. The Voc and ΔGinject parameters favoured the CLTP-dyes over corresponding PLTP-dyes, and also dyes with the N,N-diphenylaniline donor have higher Voc, ΔGinject values and longer wavelengths (λmax) than the dyes with carbazole unit (N,N-diphenylaniline dyes > Carbazole dyes) in accordance with the calculated ω-, although all the dyes have good regeneration and injection abilities

Co-Sensitization Effects of Indoline and Carbazole Dyes in Solar Cells and Their Neutral-Anion Equilibrium in Solution.

Co-sensitization of two or more light-absorbing compounds on a TiO2 surface has recently become one of the most successful strategies in the development of dye-sensitized solar cells (DSSCs). The specific structure of the dyes for DSSCs implies that they can partly exist in anionic forms in popular solvents used for sensitization. Our study concerns the above two issues being analyzed in detail using the example of the popular carbazole (MK2) and indoline (D205) dyes, studied by stationary absorption and emission, femtosecond transient absorption (in complete cells and in the solutions), current-voltage measurements, DFT and TD-DFT theoretical calculations. After the addition of D205 to DSSC with MK2, the fill factor of the cells was improved, and the electron recombination between TiO2 and the dyes was blocked (observed on sub-nanosecond time scales). Thus, the active co-adsorbent can take the role of the typically used passive additive, like chenodeoxycholic acid. Evidence of the concentration-dependent equilibrium between neutral and anionic forms of dyes with different lifetimes was found in acetonitrile solutions (the best for sensitization), while in ethanol solution the dominant form was the anion (worse for sensitization). Our findings should help in better understanding the operation and optimization of DSSC.

Synthesis, photophysical properties and two-photon absorption of benzothiazole/benzoxazole π-expanded carbazole dyes

We report the synthesis and spectroscopic characterization (NMR, HRMS) of a series of benzazole derivatives with different carbazole substituents. The photophysical properties of these molecules were investigated in several solvents of different polarity by UV–vis absorption and fluorescence spectroscopy. These dyes show strong absorption bands in the near ultraviolet region, fluorescence emission with high quantum yields in the blue-green as well as large Stokes' shifts. Two-photon absorption properties were recorded and all of the dyes show moderate TPA cross sections in the 700–800 nm zone. Molecular modeling was also used to explain spectroscopic behavior of these dyes. Interestingly, they possess high thermal stability.

Human peripheral blood mononuclear cells targeted multidimensional switch for selective detection of HSO3− anion

A new ratiometric π-conjugated luminophore with donor-acceptor (D- π- A) network CM {(E)-2-(4-(2-(9-butyl-9H-carbazol-3-yl)vinyl)benzylidine)malononitrile} has been synthesized by malononitrile conjugated carbazole dye with an intervening p-styryl spacer. Here, p-styryl conjugated malononitrile is used as a recognition site for the detection of HSO3− with a fast response time (within 50 s). In a mixed aqueous solution, CM reacts with HSO3− to give a new product 1-(9-butyl-9H-carbazol-3-yl)-2-(4-(2, 2-dicyanovinyl)phenyl)ethane-1-sulfonic acid. The probe exhibits positive solvatofluorochromism with solid state red fluorescence. The restriction of intermolecular rotation of p-styryl conjugated malononitrile unit enhances the typical solid state fluorescence properties. The probe (CM and its corresponding aldehyde CA) also demonstrates a strong solvent dependence yielding blue to green to pink and even red fluorescence in commonly used organic solvents like n-hexane, toluene, diethyl ether (DEE), THF, DCM, Dioxane, CH3CN and MeOH. The chemodosimetric approach of HSO3− selectively takes place at the olefinic carbon exhibiting a prominent chromogenic as well as ratiometric fluorescence change with a 147 nm blue-shift in the fluorescence spectrum. CM can detect HSO3− as low as 1.21 × 10−8 M. Moreover, the CM can be successfully applied to detect intrinsically generated intracellular HSO3− in human peripheral blood mononuclear cells (PBMCs). CM has shown sharp intensities (2628 ± 511.8) when the cells are HSO3− untreated. At green channel (at 486 nm) almost negligible fluorescence intensities are found (423 ± 127.5) for HSO3− untreated samples. However, the green fluorescence (2863 ± 427.5) increases significantly (p < 0.05), and simultaneously the red fluorescence gets significantly (p < 0.05) diminished (515 ± 113.2) after addition of HSO3−. The CM has been effectively utilized for evaluating the bisulfite ions in food samples as well. The concentrations of HSO3− in diluted sugar samples have been determined with the recovery of 97.6–9.12%.

Synthesis, electrochemical, optical and biological properties of new carbazole derivatives

Carbazole skeleton is the key structural motif of many biologically active compounds including synthetic and natural products. Based on the (E)-2-(2-(4-9H-carbazol-9-yl)benzylidene) hydrazinyl)thiazole as skeleton, three novel carbazole dyes were synthesized. The scientific analysis includes the effect of changing the strength of the activating substituents and their exchange for the deactivating substituent on the chemical and biological properties. The presented research showed a significant influence of the CH3, OCH3 and CH2COOC2H5 groups on the spectral properties of the tested derivatives. Their significant influence is also visible in electrochemical, nonlinear-optic and biological properties. The study also included the analysis of the use of the presented derivatives as potential fluorescent probes for in vivo and in vitro tests. Quantum-chemical calculations complement the conducted experiments.

A computational approach on engineering short spacer for carbazole-based dyes for dye-sensitized solar cells

Donor-π-linker-acceptor (D-π-A) push–pull dye molecules are most common in dye-sensitized solar cells (DSSCs) applications. Selection of dye molecules for DSSCs is based on their ability to absorb light in the visible spectrum. This can be done more efficiently by positioning the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) with respect to the conduction band of the semiconductor and the redox potential of the electrolyte, respectively. The photocurrent is manipulated by the extent of light absorption, planarity of the π-linker for efficient intramolecular charge transfer (ICT), oxidized dye reorganization energy (Λ) and dye regeneration driving force (ΔGreg). In a quest of achieving panchromatic absorption up to near-IR region, mostly electron-rich chromophores and their oligo form were used in the π-segment, but this approach led to poor ICT. In this computational analysis, we have explored the effect of electron-withdrawing (cyano (–CN)) and donating groups (methoxy (-OMe)) in three different π-segment length to understand the carbazole dyes’ suitability for DSSCs using onset wavelength (λonset), Λ, ICT and ΔGreg as the figure-of-merits.

Effect of substituents of phenyl of π-linkage in carbazole sensitizers on the photovoltaic performance of the dye-sensitized solar cells

Four novel carbazole dyes with various substituents, i.e., dyes CA, CO, CP and CB with substituents of alkyl, oxyalkyl, pillar[5]arene and hydrogen, respectively, are designed and synthesized to investigate the relationship between the substituents on phenyl of π-linkage and performances of dye-sensitized solar cells. With the different degree of deviation from planarity of the π-linkage by the substituents, the HOMO level and bandgap of the dyes were selectively tuned. The dye CO shows lower HOMO (0.66 V) and E0-0 (2.23 eV) than that of CB (HOMO: 0.97 V, E0-0: 2.52 eV), leading to the enhanced light harvesting ability and thus the highest power conversion efficiency among the four dyes. Further study shows that the bridge of carbon atoms between the substituents and phenyl in the dyes CA and CP decreased the short-circuit photocurrent, lower their performance. This study shows that the substituents can affect the torsion angle of π-linkage, the charge recombination, the electron lifetime for photoexcited electron injection into the TiO2 and VOC, which paves the way to design dyes for highly efficient solar cells.

Effect of the Chloro-Substitution on Electrochemical and Optical Properties of New Carbazole Dyes.

Carbazole derivatives are the structural key of many biologically active substances, including naturally occurring and synthetic ones. Three novel (E)-2-(2-(4-9H-carbazol-9-yl)benzylidene)hydrazinyl)triazole dyes were synthesized with different numbers of chlorine substituents attached at different locations. The presented research has shown the influence of the number and position of attachment of chlorine substituents on electrochemical, optical, nonlinear, and biological properties. The study also included the analysis of the use of the presented derivatives as potential fluorescent probes for in vivo and in vitro tests. Quantum-chemical calculations complement the conducted experiments.

Effect of different acceptors on N-hexyl carbazole moiety for dye-sensitized solar cells: design, characterization, molecular structure, and DSSC fabrications

Hexyl carbazole derivatives are one of the most prominent dye scaffolds in the dye-sensitized solar cells (DSSCs). New substituted carbazole dyes such as DRA-HC, DCA-HC, and DTC-HC were synthesized for DSSCs. These dyes are containing hexyl moiety as electron donor and rhodanine-3-acetic acid, cyanoacetic acid and tetracyanoethylene as an electron acceptor linked to carbazole moiety. The relation between dye structures, photophysical/electrochemical, molecular structure and DSSC manufacturing had been discussed. All structures showed more positive ground-state oxidation potential than I−/I−3 and more negative excited state oxidation potential than the conduction band edge of the semiconductor. The highest efficiency of the DSSCs was obtained in the case of DCA-HC dye (η = 1.41%, VOC = 708 mV, FF = 0.81, and JSC = 2.45 mA cm−2 with 100 mW cm−2) compared to other synthesized dyes.

D-A-π-A Carbazole Dyes Bearing Fluorenone Acceptor for Dye Sensitized Solar Cells

Three novel D-A-π-A carbazole sensitizing dyes were synthesized with fluorenone as the auxiliary acceptor, benzene, furan and thiophene as π bridge and cyanoacrylic acid as the anchoring acceptor. Compared with the similar D-π-A carbazole dye, the incorporation of fluorenone improved markedly the molar extinction coefficients of carbazole dyes, which increased the short-circuit current density and accordingly the photoelectric conversion efficiency. The presence of thiophene or furan bridge favors the short-circuit current density while the introduction of benzene bridge benefits the open-circuit voltage. Among three carbazole dyes, dye with benzene bridge exhibited the optimal efficiency 4.88% due to its highest open-circuit voltage and factor fill (VOC = 690 mV, JSC = 8.30 mA/cm2, and FF = 0.86).

New carbazole-based organic dyes with different acceptors for dye-sensitized solar cells: Synthesis, characterization, dssc fabrications and density functional theory studies

Carbazole dyes applied in dye-sensitized solar cells (DSSCs) are essential class of organic molecules. Two novel organic dyes DRA-BDC and DTB-BDC including rhodanine-3-acetic acid/thiobarbituric acid as electron acceptors and N, N‑butyl dicarbazole structural as electron donor/spacer have been designed as photosensitizers for DSSCs. Both prepared dyes were characterized by IR, 1H NMR, 13C NMR, mass spectroscopy and CHN analysis. Results of photophysical properties, the UV- Visible spectra of both dyes DRA-BDC and DTB-BDC showed the higher absorption peaks at 440 and 370 nm, respectively. Also, for electrochemical properties, both structures showed more +ve ground state oxidation potential than I−/I − 3, and more –ve excited state oxidation potential than the conduction band edge of the semiconductor. However, the high performance of power-conversion was observed on the DSSCs device with DRA-BDC (η = 1.16%) compared with DTB-BDC dye. Also, DRA-BDC recorded an open circuit voltage (VOC) = 589 mV, short circuit current density (JSC) = 2.46 mA/cm2 and fill factor (FF) = 0.79 under simulated AM 1.5 G irradiation (100 mW/cm2). For the theoretical studies included polarizabilities, optimization geometry, conformational analysis, and photovoltaic analysis based on frontier orbital analysis energy evaluated by using density functional theory model (DFT) with B3LYP/6–311functional basis set.

Density functional theory study on two D-π-A-type organic dyes containing different anchoring groups for dye-sensitized solar cells

The electronic structure and absorption spectra of two D-π-A-type organic dyes with different anchoring groups have been investigated using density functional theory (DFT) and time-dependent density functional theory (TD-DFT). The effect of anchoring groups on the electronic absorption of the free dyes on (TiO2)9 has been studied for the two carbazole dyes (MK1 and MK2). Results from DFT calculations indicate that hydroxamic acid anchoring group in MK2 lead to much stronger intermolecular charge transfer and adsorption energies on (TiO2)9 cluster. The effect of four different XC functionals (B3LYP, ωB97xD, M06-2X, and CAM-B3LYP) on the transition energies has been tested in order to explore the valid functional for the studied system. The wavelength values from the ωB97xD/6-31+G** level of theory are in excellent agreement with experimental data so this functional was considered to calculate the electronic absorption of the two studied dyes. The highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO), and the gap energy (H–L) of the studied dyes are slightly influenced by change of anchoring group. Results reveal that the LUMO energy levels of all studied dyes are higher than the conduction band (CB) of TiO2 (− 4.00 eV). Deprotonation process enhances the efficiency of dye-sensitized solar cells during decreasing adsorption energy of dyes with (TiO2)9 cluster.

Molecular engineering of pyrene carbazole dyes with a single bond and double bond as the mode of linkage

Both carbazole and pyrene are electron-rich aromatic systems and are expected to be potential donors when used in push–pull dye architecture in the field of DSSC.

Molecular engineering of the alkyl chain in planar carbazole dyes toward efficient interfacial charge transfer processes

With the extension of the alkyl chain, the interfacial charge transfer processes are effectively improved.

Design and photoelectric properties of D-A-π-A carbazole dyes with different π-spacers and acceptors for use in solar cells: a DFT and TD-DFT investigation.

Density functional theory (DFT) and time-dependent DFT (TD-DFT) were used to calculate the properties of the carbazole dyes TYZ-1 to TYZ-5, which differed in their π-spacers. The carbazole dyes TYZ-6 and TYZ-7 were then designed; these were based on TYZ-3 (which had 2,2':5',2″-terthiophene as its π-spacer) but had more strongly electron-withdrawing second acceptor groups than TYZ-3. All of these dyes except for TYZ-5 presented quasi-planar conformations, and the calculated energies of their highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) molecular orbitals as well as their HOMO-LUMO gaps (Eg) suggest that these dyes are suitable for use as sensitizers. Lengthening the π-spacer and increasing its degree of conjugation were found to cause the absorption spectrum of the dye to redshift and to facilitate hole injection. The Eg values of TYZ-6 and TYZ-7 were calculated to be smaller than that of TYZ-3 due to the weaker electron-withdrawing power of the second acceptor group in TYZ-3, and the dyes TYZ-2, TYZ-3, TYZ-6, and TYZ-7 presented the smallest Eg values. Local electron excitations following UV-vis absorption led to electronic transitions, particularly HOMO to LUMO transitions (> 94.3% of all transitions). The excited states of these dyes were found to have quasi-planar conformations, although their dihedral angles were smaller than those in the corresponding ground states. The Stokes Shifts calculated for the seven dyes (which ranged from 51.9 to 98.1nm) suggested that self-absorption was unlikely to occur. Overall, the calculations indicated that the dyes TYZ-2, TYZ-3, TYZ-6, and TYZ-7 are promising candidates for use in dye-sensitized solar cells.

A theoretical investigation of the optoelectronic performance of some new carbazole dyes

Density functional theory and time-dependent approaches are applied for theoretical investigation of a new class of novel carbazole-based d–D–π–A-type dyes, where the carbazole moiety is the main electron donor, bithiophene behaves as a π-bridge, and cyanoacetic acid as an electron acceptor for all the studied dyes, whereas the terminal electron donor unit is varied to thiophene, thienothiophene, carbazole, dimethoxyphenyl, and indole. The influence of the terminal electron donor on the optoelectronics properties is investigated for the dyes in isolated state and in chloroform solvent. Their absorption spectra and electronic and structural properties are evaluated and discussed. The theoretical results show that all the dyes exhibit excellent optoelectronic properties. In particular, D5 with indole as the terminal electron donor moiety has potential for use as a sensitizer for nanocrystalline TiO2 solar cells based on its red-shifted absorption spectrum, reduced energy gap, lowest λtotal value, and higher $$\Delta G^{\text{Inject}}$$ and $$\Delta G^{\text{Reg}}$$ values.

Donor-π-Conjugated Spacer-Acceptor Dye-Sensitized Solid-State Solar Cell Using CuI as the Hole Collector

Dye-sensitized solid-state solar cells (DSSCs) replacing the liquid electrolyte with a p-type semiconductor have been extensively examined to solve the practical problems associated with wet-type solar cells. Here, we report the fabrication of a solid-state solar cell using copper iodide (CuI) as the hole conductor and alkyl-functionalized carbazole dye (MK-2) as the sensitizer. A DSSC sensitized with MK-2 showed a solar-to-electrical power conversion efficiency of 3.33% with a Voc of 496 mV and a Jsc of 16.14 mA cm-2 under AM 1.5 simulated sunlight. The long alkyl chains act as a barrier for charge recombination, and the strong accepting and donating abilities of the cyanoacrylic and carbazole groups, respectively, enhance the absorption of light at a longer wavelength, increasing the short-circuit current density. The efficiency recorded in this work is higher than similar DSSCs based on other hole collectors.

Theoretical insight on hybrid nanocomposites of graphene quantum dot and carbazole-carbazole dyes as an efficient sensitizer of DSSC.

The feasibility of the hybrid nanocomposites of the graphene quantum dot (GQD) and carbazole-carbazole dyes as the efficient sensitizer of dye-sensitized solar cells (DSSC) is investigated. By using the first principles density functional theory (DFT), we fully optimize the geometrical structures of GQD, the carbazole-carbazole dyes, and their hybrid nanocomposites. The harmonic frequency analysis is used to confirm the energy stability of the optimized structures. The optical absorptions of the structures are calculated with the time-dependent DFT (TDDFT). Using the I-/I3- electrolyte and the conduction band minimum of TiO2 electrode as a sample, we examine the feasibility of the nanocomposites as the sensitizer of DSSC with the charge spatial separation and the molecular orbital energy levels of the nanocomposites. The results demonstrate all the considered nanocomposites have suitable energy levels of the frontier orbitals and significantly charge spatial separation. TDDFT results show the oscillator strengths of all nanocomposites demonstrate the obvious enhancement in the visible light region. Moreover, the appropriate open-circuit voltage value, the larger light-harvesting efficiency, and larger driving force are also identified for these nanocomposites. Therefore, the nanocomposites could be the more promising candidates of sensitizer for DSSC in comparison with the separate carbazole-carbazole dyes.

Aggregation induced light harvesting of molecularly engineered D-A-π-A carbazole dyes for dye-sensitized solar cells

Novel class of metal free organic dyes (CCTh and CCBz) with D-A-π-A configuration, having carbazole as donor and 3-cyanopyridine as auxiliary acceptor replacing conventional benzannulated heterocycles along with variable π-linkers were synthesized and used in dye-sensitized solar cells (DSSCs). Both the dyes are having cyanoacrylic acid as the anchoring group with thiophene (CCTh) and phenylene (CCBz) as π-linkers. The photophysical, electrochemical, theoretical and photovoltaic properties of the dyes were investigated in detail. The absorption spectra of dyes on TiO2 showed broader absorption band for CCTh in comparison to the solution spectra indicating aggregation in solid state. The aggregation studies in varied THF/water fraction indicates J-aggregation for both the dyes. CCTh with thiophene linker showed broader absorption compared to CCBz, and the photovoltaic performance recorded for CCTh directly indicates better light harvesting ability corresponding to the red shifted J-aggregated states. Hence, solar cells fabricated with CCTh gave a power conversion efficiency of 3.39% and CCBz delivered an efficiency of 2.03% under full sun condition. A detailed investigation of device dynamics have been carried out employing charge extraction (CE), intensity-modulated photovoltage spectroscopy (IMVS) and open-circuit voltage decay (OCVD) measurements.

Low cost and efficient hetero-anthracene based small organic hole transporting materials for solid state photoelectrochemical cells

A series of low cost phenothiazine (PTZ) based small organic hole transporting materials (OHTMs) with high conductivity, hole mobility and low crystallinity were synthesized and systematically investigated for solid state photoelectrochemical cells/dye sensitized solar cells (DSSCs). Thermal, optical, photoelectrical and electrochemical properties of all OHTMs were evaluated using thermal techniques, cyclic voltammetry (CV), UV–vis absorption and other techniques. Density functional theory (DFT) was used to calculate optical and electrochemical properties of OHTMs and compared with experimental data. Role of these OHTMs in solid state photoelectrochemical cells with metal-free carbazole dye, SK3 in presence of additives like lithium bis(trifluoromethyl sulfonyl)imide salt (LiTFSI) and tert-butyl pyridine (TBP) are discussed along with the thickness of photoanode. In order to take an insight into photovoltaic performance, electron transfer kinetics and electron recombination in the OHTMs with different thickness of TiO2 thin film based ss-DSSCs were characterized by I–V, electrochemical impedance spectroscopy (EIS) and open circuit voltage decay (OCVD). The hole mobility, conductivity and photovoltaic performance of OHTMs are comparable with commercially available Spiro-OMeTAD. The highest power conversion efficiency (PCE), 4.91% is achieved from thiophene substituted (at 3,6 positions) phenothiazine based SJH-11, is comparable with reference device incorporating Spiro-OMeTAD as HTM with SK3 sensitizer. All the ss-DSSCs with OHTMs exhibit good long-term stability under 1 sun illumination and ambient humidity conditions. The results are promising and have scope for improvement upon optimization of substitution at 3 and 6 positions of PTZ central/core moiety.