Phenothiazine functional materials for organic optoelectronic applications

Near-IR Capturing N-Methylbenzene Sulfonamide-Phenothiazine Incorporating Strong Electron Acceptor Push-Pull Systems: Photochemical Ultrafast Carrier Dynamics

Unraveling the intriguing aspects of the intramolecular charge transfer (ICT) phenomenon of multi-modular donor-acceptor-based push-pull systems are of paramount importance considering their promising applications, particularly in solar energy harvesting and light-emitting devices. Herein, a series of symmetrical and unsymmetrical donor-acceptor chromophores 1-6, are designed and synthesized by the Corey-Fuchs reaction via Evano's condition followed by [2+2] cycloaddition retroelectrocyclic ring-opening reaction with strong electron acceptors TCNE and TCNQ in good yields (~60-85 %). The photophysical, electrochemical, and computational studies are investigated to explore the effect of incorporation of strong electron acceptors 1,1,4,4-tetracyanobuta-1,3-diene (TCBD) and dicyanoquinodimethane (DCNQ) with phenothiazine (PTZ) donor. An additional low-lying broad absorption band extended towards the near-infrared (NIR) region suggests charge polarization after the introduction of the electron acceptors in both symmetrical and asymmetrical systems, leading to such strong ICT bands. The electrochemical properties reveal that reduction potentials of 3 and 6 are lower than those of 2 and 5, suggesting DCNQ imparts more on the electronic properties and hence largely contributes to the stabilization of LUMO energy levels than TCBD, in line with theoretical observations. Relative positions of the frontier orbitals on geometry-optimized structures further support accessing donor-acceptor sites responsible for the ICT transitions. Eventually, ultrafast carrier dynamics of the photoinduced species are investigated by femtosecond transient absorption studies to identify their spectral characteristics and target analysis further provides information about different excited states photophysical events including ICT and their associated time profiles. The key findings obtained here related to excited state dynamical processes of these newly synthesized systems are believed to be significant in advancing their prospect of utilization in solar energy conversion and related photonic applications.

Polyacetylenes with (hetero)aryl-, styryl-, and amino-phenothiazinyl sidechains: synthesis and photophysics

A novel generation of 7-aryl phenothiazinyl substituted polyacetylenes is readily accessible via controlled rhodium-catalyzed polymerization of the corresponding 3-ethynyl 7-aryl phenothiazines. The monomers are synthesized by Suzuki coupling, Heck coupling, or Buchwald-Hartwig amination, and Bestmann-Ohira reaction. This allows for the introduction of electron donating and releasing substituents with different ligation patterns. The obtained polymers display narrow molecular weight distributions, with very few exceptions, and are soluble in many organic solvents. The photophysical properties of novel monosubstituted polyacetylenes and corresponding monomers were compared. While the monomers exhibit strong emission in solution with quantum yields of up to 0.84 only selected polymers are luminescent (Φf = 0.06) and display moderate Stokes shifts and positive emission solvatochromism.

Synthesis and Photophysical Properties of Luminescent Phenothiazinyl Merocyanine Substituted Polyacetylenes

A new generation of soluble phenothiazinyl merocyanine substituted polyacetylenes can be readily synthesized by rhodium-catalyzed polymerization of the corresponding 3-ethynyl phenothiazines, accessible by Sonogashira coupling and Knoevenagel condensation. UV/Vis and fluorescence spectroscopy of 7-acceptor-substituted phenothiazinyl polyacetylenes reveal that these polyacetylenes with conjugatively ligated merocyanines are luminescent in solution with positive emission solvatochromism and, in some cases, with distinct solid-state luminescence.

Recent Advances in Monocomponent Visible Light Photoinitiating Systems Based on Sulfonium Salts

During the last decades, multicomponent photoinitiating systems have been the focus of intense research efforts, especially for the design of visible light photoinitiating systems. Although highly reactive three-component and even four-component photoinitiating systems have been designed, the complexity to elaborate such mixtures has incited researchers to design monocomponent Type II photoinitiators. Using this approach, the photosensitizer and the radical/cation generator can be combined within a unique molecule, greatly simplifying the elaboration of the photocurable resins. In this field, sulfonium salts are remarkable photoinitiators but these structures lack absorption in the visible range. Over the years, various structural modifications have been carried out in order to redshift their absorptions in the visible region. In this work, an overview of the different sulfonium salts activable under visible light and reported to date is proposed.

Near-IR absorbing 1,1,4,4-tetracyanobutadiene-functionalized phenothiazine sulfones

Triphenylamine (TPA) substituted π-conjugated chromophores TPA1-TPA5 were designed and synthesized via Pd-catalysed Sonogashira cross-coupling followed by [2 + 2] cycloaddition-retroelectrocyclization (CA-RE) reactions. The effects of acceptor 1,1,4,4-tetracyanobutadiene (TCBD) and cyclohexa-2,5-diene-1,4-diylidene-expanded TCBD (DCNQ) units in the photophysical studies and the HOMO-LUMO energy levels of the phenothiazine sulfones TPA1-TPA5 were evaluated. The absorption spectra of chromophores TPA4 and TPA5 show a significant change due to the incorporation of DCNQ units, resulting in bathochromically shifted broad absorption in the NIR region. The photophysical studies revealed that DCNQ-based chromophores TPA4 and TPA5 have a better D-A interaction than the TCBD functionalized TPA2 and TPA3. Density functional theory calculations and electrochemical studies were performed to examine the molecular geometry and frontier energy levels of the sulfone-based chromophores. Systematic structural modification of the chromophore TPA1 modulated the electrochemical properties and successively tuned the energy gaps for TPA2-TPA5. The theoretically estimated HOMO-LUMO gaps for TPA1-TPA5 exhibit good agreement with the experimental data calculated from the electrochemical studies. The chromophore TPA1 exhibits solvatochromism and aggregation-induced emission (AIE) behavior owing to the emission in the solid state.

Development of a push-π-pull phenothiazine-vinyl-isophorone fluorophore: a novel solvatochromic and pH indicator

Knoevenagel condensation of phenothiazine-3,7-dicarbaldehyde with an isophorone yielded a new phenothiazine derivative (PTZ-c) fluorophore. The solvatochromic and pH-sensing abilities of PTZ-c, an asymmetric fluorophore with a single isophorone molecule, were shown to be exceptional. PTZ-c produced very delicate absorbance and emission spectra. When the polarity of the solvent was increased, the PTZ-c emission spectra showed greater sensitivity than the absorption spectra. Multiple spectroscopic techniques, including Fourier transform infrared spectroscopy, nuclear magnetic resonance, and mass spectrometry, were used to characterize the manufactured PTZ-c sensor. To demonstrate the beneficial solvatochromic behaviour associated with intramolecular charge transfer, the absorption spectra of the synthesized DA PTZ-c dye were analyzed in different solvents of varying polarity. Band intensity and the wavelength of PTZ-c emission were also found to be highly solvent dependent. It was observed that when solvent polarity was increased to a maximum of 4122 cm^-1 , Stokes' shift also increased. To analyze the Stokes' shift that depended on the solvent, a linear correlation between solvation and energy was used. An investigation of PTZ-c quantum yield (ф) was also conducted. Both the absorbance and fluorescence spectra of the sensor in dimethylformamide as a function of pH were studied. A fluorescence peak was seen at 562 nm, whereas the greatest absorption wavelengths were found at 403 and 317 nm. It was shown that the pH-sensing mechanism depended on protons removed from the PTZ-c chromophore, which caused a colour shift and variation in both emission and colorimetric properties.

Experimental spectra, electronic properties (liquid and gaseous phases) and activity against SARS-CoV-2 main protease of Fluphenazine dihydrochloride: DFT and MD simulations

The Gaussian 09 DFT tool is used to investigate the formational electronic behaviour, reactivity analysis and biological properties of fluphenazine dihydrochloride (FDD). The quantum computation is used to determine the spectroscopic and vibrational assignments of FDD. The NBO method explains charge transfer and molecular interactions. Energy gap values are determined using FMO analysis in different solvents and toluene is a better solvent due to higher value of solvation energy. The UV-visible spectra are investigated in various solvents using the TD-DFT method. Electrostatic potential, the wave function related properties such as LOL, NCI and RDG are determined in gaseous phase. Furthermore, the drug likeness is analyzed. At last, a docking study with MD simulation is used to investigate FDD's antiviral activity against SARS-CoV-2 main protease.

Engineering of W-shaped benzodithiophenedione-based small molecular acceptors with improved optoelectronic properties for high efficiency organic solar cells

In the current study, with the objective to improve the overall performance of organic solar cells, seven new W-shaped small molecular acceptors – were developed theoretically by the end-group alteration of the reference (WR) molecule. The MPW1PW91 functional with the basis set 6-31G(d,p) was used to explore the optoelectronic properties of the WR and W1–W7 molecules and the time-dependent self-consistent filed (TD-SCF) simulation was used to investigate the solvent-state calculations. The several explored photovoltaic attributes were the absorption spectra, excitation energies, bandgap between the FMOs, oscillator strength, full width at half maximum, light-harvesting efficiency, transition density matrices, open-circuit voltage, fill factor, density of states, binding energy, interaction coefficient, etc. Overall, the results revealed a bathochromic shift in the absorption maxima (λ_max), a reduced HOMO–LUMO gap (E_gap), and smaller excitation energy (E_x) of the altered molecules as compared to the WR molecule. Some of the optoelectronic aspects of a well-known fused ring based acceptor named Y6 are also compared with the studied W-shaped molecules. Additionally, the W1 molecule presented the smallest E_gap, along with highest λ_max and the lowest E_x, amongst all, in both the evaluated media (gas and solvent). The open circuit voltage (V_OC) of all the considered small molecular acceptors was calculated by pairing them with the PTB7-Th donor. Here, W6 and W7 displayed the best results for the V_OC (1.48 eV and 1.51 eV), normalized V_OC (57.25 and 58.41) and FF (0.9131 and 0.9144). Consequently, in light of the results of this research, the altered molecules could be considered for practical implementation in the manufacturing of OSCs with improved photovoltaic capabilities.

The developed molecules have a reduced band gap and lower excitation energy. Their V_OC was calculated by making complexes of them with the PTB7-Th donor.

Synthesis and Luminescent Properties of 1,4,5-Triphenylimidazole‒Phenothiazine Fluorophores

Two blue donor-acceptor fluorophores with 1,4,5-triphenylimidazole as the electron-transporting unit and phenothiazine as the hole-transporting unit were synthesized by grafting 1,4,5-triphenylimidazole moieties onto 3- and 3,7-position of the phenothiazine core and characterized by spectroscopic methods. Their thermal stability, photophysical, electrochemical and electroluminescence properties were systematically investigated. These compounds exhibit good thermal stability and show blue emission in dichloromethane solution and thin solid films. The solution-processed doped devices were fabricated by using these fluorophores as the emitting dopant in 1,3-bis(N-carbazolyl)benzene host, in which the device fabricated from the fluorophore containing two 1,4,5-triphenylimidazole moieties exhibited blue emission with a luminance of 648 cd/m² and external quantum efficiency of 1.48%.

Synergistic end-capped engineering on non-fused thiophene ring-based acceptors to enhance the photovoltaic properties of organic solar cells

The computational analysis revealed the bathochromic shift of the UV-visible absorption, reduced band gap have and increased LHE of all developed molecules as compared to the reference molecule. VOC was calculated by making their complex of molecules with PTB7-Th donor.

Phenothiazine and phenothiazine-5,5-dioxide based push-pull Derivatives: Synthesis, photophysical, electrochemical and computational Studies

A set of phenothiazine (PTZ) and phenothiazine-5,5-dioxide based π-conjugated push–pull chromophores PTZ 1–6 were designed and synthesized by the Pd-catalyzed Sonogashira cross-coupling and [2+2] cycloaddition retroelectrocyclic ring opening reaction in...

Extended phenothiazines: synthesis, photophysical and redox properties, and efficient photocatalytic oxidative coupling of amines

Herein, we successfully developed a ring-fusion approach to extend the conjugation length of phenothiazines that were demonstrated to be efficient photocatalysts for visible-light-driven oxidative coupling reactions of amines under an air atmosphere.

Double Heterohelicenes Composed of Benzo[b]- and Dibenzo[b,i]phenoxazine: A Comprehensive Comparison of Their Electronic and Chiroptical Properties

Heterohelicenes are potential materials in molecular electronics and optics because of their inherent chirality and various electronic properties originating from the introduced heteroatoms. In this work, we comprehensively investigated two kinds of double NO-hetero[5]helicenes composed of 12H-benzo[b]phenoxazine (BPO) and 13H-dibenzo[b,i]phenoxazine (DBPO). These helicenes exhibit good electron-donor properties reflecting the electron-rich character of their monomers and were demonstrated to work as p-type semiconductors. The enantiomers of these helicenes show the largest class of dissymmetry factors for circularly polarized luminescence (CPL) (|g_CPL| > 10^-2) among helicenes reported to date. Interestingly, the signs of CPL are opposite for BPO and DBPO double helicenes of the same helicity. The origin of the large g_CPL values and the inversion of the CPL sign was addressed by analysis of the transition electronic dipole moments and transition magnetic dipole moments based on TD-DFT calculations.

Structural Geometry Variation of 1,4-Naphthalene-Based Co-Polymers to Tune the Device Performance of PVK-Host-Based OLEDs

Blue-color-emitting organic semiconductors are of significance for organic light-emitting diodes (OLEDs). In this study, through Suzuki coupling polymerization, three 1,4-naphthalene-based copolymers-namely, PNP(1,4)-PT, PNP(1,4)-TF, and PNP(1,4)-ANT-were designed and synthesized. The variation of comonomers, phenothiazine (PT), triphenylamine substituted fluorene (TF), and anthanthrene (ANT), effectively tuned the emitting color and device performance of poly(9-vinyl carbazole) (PVK)-based OLEDs. Especially, the polymer PNP(1,4)-TF, bearing perpendicular aryl side groups, showed a most twisted structural geometry, which enabled an ultra-high thermal stability and a best performance with blue emitting in PVK-host-based OLEDs. Overall, in this work, we demonstrate a promising blue-color-emitting polymer through structural geometry manipulation.