Selective Tuning of the HOMO-LUMO Gap of Carbazole-Based Donor-Acceptor-Donor Compounds toward Different Emission Colors

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.

NIR-Absorbing 1,1,4,4-Tetracyanobuta-1,3-diene- and Dicyanoquinodimethane-Functionalized Donor-Acceptor Phenothiazine Derivatives: Synthesis and Characterization

A series of symmetrical and unsymmetrical donor-acceptor type phenothiazine derivatives 1-18 were designed and synthesized via Pd-catalyzed Sonogashira cross-coupling and [2 + 2] cycloaddition-retroelectrocyclization reactions. The incorporation of cyano-based acceptors 1,1,4,4-tetracyanobutadiene (TCBD) and dicyanoquinodimethane (DCNQ) in the phenothiazine derivatives resulted in systematic variation in the photophysical, thermal, and electrochemical properties. The electronic absorption spectra of the phenothiazine derivatives with strong acceptors 2, 3, 5, 6, 8, 9, 11, 12, 14, 15, 17, and 18 show red-shifted absorption as compared to phenothiazine derivatives 1, 4, 7, 10, 13, and 16 in the near-IR region due to a strong intramolecular charge transfer (ICT) transition. The electrochemical analysis of the phenothiazine derivatives 2, 3, 5, 6, 8, 9, 11, 12, 14, 15, 17, and 18 reveals two reduction waves at low potential due to the TCBD and DCNQ acceptors. The mono-TCBD-functionalized phenothiazine 2 shows higher thermal stability compared to other phenothiazine derivatives. The computational studies on phenothiazines 1-18 reveal the LUMO is substantially stabilized as acceptor strength increases, which lowers the HOMO-LUMO gap.

Size economy and first hyperpolarizability: synthesis and nonlinear optical behavior of ferrocene-based donor-acceptor chromophores lacking π-linkers

The question of size economy in the design of chromophores for nonlinear optics is addressed in this investigation. We have synthesized directly linked donor-acceptor dyads, which lack a π-conjugated linker, the presence of which is usually considered obligatory in materials designed for nonlinear optics. Correlating linear optical data, electrochemical data, computational data and hyper Rayleigh scattering (HRS) data on ferrocene (Fc) based dyads, we demonstrate that the first hyperpolarizability of such size economical chromophores is significantly better compared to that of Fc based, traditional, larger, donor-π-acceptor chromophores. Arguably, a larger π-conjugated linker decreases the electronic communication between the donor and the acceptor and weakens the intramolecular charge transfer in such chromophores.

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...

Triphenylamine-Merocyanine-Based D1-A1-π-A2/A3-D2 Chromophore System: Synthesis, Optoelectronic, and Theoretical Studies

donor⁻acceptorDonor⁻acceptor⁻π⁻acceptor⁻donor (D1-A1-π-A2/A3-D2)-type small molecules, such TPA-MC-2 and TPA-MC-3, were designed and synthesized starting from donor-substituted alkynes (TPA-MC-1) via [2 + 2] cycloaddition-retroelectrocyclization reaction with tetracyanoethylene (TCNE) and 7,7,8,8-tetracyanoquinodimethane (TCNQ) units, respectively. TPA-MC-2 and TPA-MC-3 chromophores differ on the A2/A3 acceptor subunit, which is 1,1,4,4-tetracyanobutadiene (TCBD) and a dicyanoquinodicyanomethane (DCQDCM), respectively. Both the derivative bearing same donors D1 (triphenylamine) and D2 (trimethylindolinm) and also same A1 (monocyano) as an acceptor, tetracyano with an aryl rings as the π-bridging moiety. The incorporation of TCNE and TCNQ as strong electron withdrawing units led to strong intramolecular charge-transfer (ICT) interactions, resulting in lower LUMO energy levels. Comparative UV⁻Vis absorption, fluorescence emission, and electrochemical and computational studies were performed to understand the effects of the TCNE and TCNQ subunits incorporated on TPA-MC-2 and TPA-MC-3, respectively.

Synthesis and characterization of new D–π-A and A–π-D–π-A type oligothiophene derivatives

New conjugated oligothiophenes with different donor/acceptor architectures were synthesized, with potential applications in the field of organic electronics.

Tetracyanobutadiene (TCBD) functionalized benzothiadiazole derivatives: effect of donor strength on the [2+2] cycloaddition–retroelectrocyclization reaction

A series of unsymmetrical and symmetrical mono/di 1,1,4,4-tetracyanobutadiene (TCBD) substituted benzothiadiazoles (BTDs) 2a–2g was synthesized by [2+2] cycloaddition–retroelectrocyclization reaction.

Mechanism of Ligand-Controlled Emission in Silicon Nanoparticles

Although bulk silicon (Si) is known to be a poor emitter, Si nanoparticles (NPs) exhibit size-dependent photoluminescence in the red or near-infrared due to quantum confinement. Recently, it has been shown that surface modification of Si NPs with nitrogen-capped ligands results in bluer emission wavelengths and quantum yields of up to 90%. However, the emission mechanism operating in these surface-modified Si NPs and the factors that determine their emission maxima are still unclear. Here, the emission in these species is shown to arise from a charge-transfer state between the Si surface and the ligand. The energy of this state is linearly correlated to the calculated ground-state dipole moment of the free ligand. This trend can be used in a predictive fashion for the design and synthesis of Si NPs with a broader range of emission wavelengths.

Targeting β-amyloid plaques and oligomers: development of near-IR fluorescence imaging probes

Evidence indicated that shifting treatment to a presymptomatic stage may produce significant benefits to prevent/alleviate the progression of Alzheimer's disease (AD); in particular, early incorporation of noninvasive imaging and biomarker testing will be significantly beneficial for AD drug development. Based on amyloid cascade hypothesis and its revised version, both β-amyloid deposition and soluble oligomeric species could be good diagnostic biomarkers for AD. Near-IR fluorescence (NIRF) imaging, which so far is limited to animal studies, is a promising method for its incomparable advantages such as low cost, high-throughput and easy operation. This review focuses on recent reported NIRF probes that showed excellent binding to plaques and oligomers. We hope that this review will shed light on the future of NIRF probes' discovery.

C2-Symmetric ferrocenyl bisthiazoles: synthesis, photophysical, electrochemical and DFT studies

A series of donor-acceptor ferrocenyl substituted bisthiazoles 3-8 were designed and synthesized by the Pd-catalyzed Suzuki, Heck, and Sonogashira cross-coupling reactions. Their photophysical, electrochemical and computational studies reveal strong donor-acceptor interactions. The photonic and electrochemical studies show that the ferrocenyl bisthiazoles with vinyl linkage ferrocenyl-bisthiazole 4, show better electronic communication compared to rest of the ferrocenyl bisthiazoles. The time dependent density functional theory (TD-DFT) calculation at B3LYP on the ferrocenyl substituted bisthiazoles 3-5 was performed, in which the ferrocenyl-bisthiazole 4 shows strong donor-acceptor interactions compared to the Fc-bisthiazoles 3 and 5. The thermal stability of the ferrocenyl substituted bisthiazoles 3-8 is reported, in which Fc-bisthiazole 8 shows high thermal stability. The single crystal structures of ferrocenyl-bisthiazoles 3 and 5 are reported.

Unsymmetrical Donor-Acceptor-Acceptor-π-Donor Type Benzothiadiazole-Based Small Molecule for a Solution Processed Bulk Heterojunction Organic Solar Cell

A D1-A-A'-π-D2 type (D = donor; A = acceptor) unsymmetrical small molecule denoted as BTD3 containing different end group donor moieties has been designed and synthesized for use as a donor in the solution processable bulk heterojunction (BHJ) solar cell. The BTD3 exhibits a low HOMO-LUMO gap of 1.68 eV and deeper HOMO energy level (-5.5 eV). Its LUMO energy level (-3.65 eV) is compatible with the LUMO level of PC71BM to facilitate the electron transfer from BTD3 to PC71BM in the BHJ solar cell. The solution processed BHJ solar cell with optimized BTD3:PC71BM active layer processed with THF solvent exhibited a PCE of 3.15% with Jsc = 7.45 mA/cm(2), Voc = 0.94 V, and FF = 0.45. Moreover, the device with optimized concentration of 3 vol. % 1-chloronaphthalene (CN) additive, i.e., CN/THF, showed significant enhancement in PCE up to 4.61% (Jsc = 9.48 mA/cm(2), Voc = 0.90 V, and FF = 0.54). The improvement in the PCE has been attributed to the appropriate nanoscale phase separation morphology, balance charge transport, and enhancement in the light harvesting ability of the active layer.

Controllable growth of organic nanostructures from 0D to 1D with different optical properties

Controllable nano/microstructures from 0D to 1D were fabricated by adjusting the growth rate. The difference in symmetry between two molecules results in distinct self-assembly behaviours and different optical properties.

Aryl-substituted symmetrical and unsymmetrical benzothiadiazoles

The incorporation of a planar anthracene unit lowers the HOMO–LUMO gap and improves the thermal stability of donor–acceptor benzothiadiazoles.

Synthesis and studies of electrochemical properties of lophine derivatives

A versatile series of lophine derivatives (1–13) were synthesized and characterized, Fourier transform infrared spectroscopy (FTIR), Liquid Chromatography-Mass Spectrometry (LC-MS), and ¹H and ¹³C nuclear magnetic resonance (NMR) spectroscopy.

Micellar charge induced emissive response of a bio-active 3-pyrazolyl-2-pyrazoline derivative: a spectroscopic and quantum chemical analysis

HOMO–LUMO distribution of PYZ in its ground and first singly excited state.

Arylethynyl receptors for neutral molecules and anions: emerging applications in cellular imaging

This critical review will focus on the application of shape-persistent receptors for anions that derive their rigidity and optoelectronic properties from the inclusion of arylethynyl linkages. It will highlight a few of the design strategies involved in engineering selective and sensitive fluorescent probes and how arylacetylenes can offer a design pathway to some of the more desirable properties of a selective sensor. Additionally, knowledge gained in the study of these receptors in organic media often leads to improved receptor design and the production of chromogenic and fluorogenic probes capable of detecting specific substrates among the multitude of ions present in biological systems. In this ocean of potential targets exists a large number of geometrically distinct anions, which present their own problems to the design of receptors with complementary binding for each preferred coordination geometry. Our interest in targeting charged substrates, specifically how previous work on receptors for cations or neutral guests can be adapted to anions, will be addressed. Additionally, we will focus on the design and development of supramolecular arylethynyl systems, their shape-persistence and fluorogenic or chromogenic optoelectronic responses to complexation. We will also examine briefly how the "chemistry in the cuvet" translates into biological media (125 references).