Perspectives on push-pull chromophores derived from click-type [2 + 2] cycloaddition-retroelectrocyclization reactions of electron-rich alkynes and electron-deficient alkenes

Various push-pull chromophores can be synthesized in a single and atom-economical step through [2 + 2] cycloaddition-retroelectrocyclization (CA-RE) reactions involving diverse electron-rich alkynes and electron-deficient alkenes. In this review, a comprehensive investigation of the recent and noteworthy advancements in the research on push-pull chromophores prepared via the [2 + 2] CA-RE reaction is conducted. In particular, an overview of the physicochemical properties of the family of these compounds that have been investigated is provided to clarify their potential for future applications.

Tetracyanobutadiene Bridged Push-Pull Chromophores: Development of New Generation Optoelectronic Materials

This review describes the design strategies used for the synthesis of various tetracyanobutadiene bridged donor-acceptor molecular architectures by a click type [2+2] cycloaddition-retroelectrocyclization (CA-RE) reaction sequence. The photophysical and electrochemical properties of the tetracyanobutadiene bridged molecular architectures based on various moieties including diketopyrrolopyrrole, isoindigo, benzothiadiazole, pyrene, pyrazabole, truxene, boron dipyrromethene (BODIPY), phenothiazine, triphenylamine, thiazole and bisthiazole are summarized. Further, we discuss some important applications of the tetracyanobutadiene bridged derivatives in dye sensitized solar cells, bulk heterojunction solar cells and photothermal cancer therapy.

Fusing pyrene and ferrocene into a chiral, redox-active triangle

A macrocycle that integrates three ferrocene-pyrene dyads in a triangular C2-symmetric arrangement is synthesised as a racemate in a simple one-pot approach. Crystal structural analysis reveals two enantiomeric conformers that pack alternatingly via π-π stacking and interconvert dynamically in solution. Electrochemical investigations indicate weak electrostatic interactions between Fc groups upon oxidation to a mixed valence triangle.

Triphenylamine/Tetracyanobutadiene-Based π-Conjugated Push-Pull Molecules End-Capped with Arene Platforms: Synthesis, Photophysics, and Photovoltaic Response

π-Conjugated push-pull molecules based on triphenylamine and 1,1,4,4-tetracyanobuta-1,3-diene (TCBD) have been functionalized with different terminal arene units. In solution, these highly TCBD-twisted systems showed a strong internal charge transfer band in the visible spectrum and no detectable photoluminescence (PL). Photophysical and theoretical investigations revealed very short singlet excited state deactivation time of ≈10 ps resulting from significant conformational changes of the TCBD-arene moiety upon photoexcitation, opening a pathway for non-radiative decay. The PL was recovered in vacuum-processed films or when the molecules were dispersed in a PMMA matrix leading to a significant increase of the excited state deactivation time. As shown by cyclic voltammetry, these molecules can act as electron donors compared to C₆₀ . Hence, vacuum-processed planar heterojunction organic solar cells were fabricated leading to a maximum power conversion efficiency of ca. 1.9 % which decreases with the increase of the arene size.

Ferrocenyl-Pyrenes, Ferrocenyl-9,10-Phenanthrenediones, and Ferrocenyl-9,10-Dimethoxyphenanthrenes: Charge-Transfer Studies and SWCNT Functionalization

The synthesis of 1-Fc- (3), 1-Br-6-Fc- (5 a), 2-Br-7-Fc- (7 a), 1,6-Fc₂ - (5 b), 2,7-Fc₂ -pyrene (7 b), 3,6-Fc₂ -9,10-phenanthrenedione (10), and 3,6-Fc₂ -9,10-dimethoxyphenanthrene (12; Fc=Fe(η⁵ -C₅ H₄ )(η⁵ -C₅ H₅ )) is discussed. Of these compounds, 10 and 12 form 1D or 2D coordination polymers in the solid state. (Spectro)Electrochemical studies confirmed reversible Fc/Fc⁺ redox events between -130 and 160 mV. 1,6- and 2,7-Substitution in 5 a (E°'=-130 mV) and 7 a (E°'=50 mV) influences the redox potentials, whereas the ones of 5 b and 7 b (E°'=20 mV) are independent. Compounds 5 b, 7 b, 10, and 12 show single Fc oxidation processes with redox splittings between 70 and 100 mV. UV/Vis/NIR spectroelectrochemistry confirmed a weak electron transfer between Fe^II /Fe^III in mixed-valent [5 b]⁺ and [12]⁺ . DFT calculations showed that 5 b non-covalently interacts with the single-walled carbon nanotube (SWCNT) sidewalls as proven by, for example, disentangling experiments. In addition, CV studies of the as-obtained dispersions confirmed exohedral attachment of 5 b at the SWCNTs.

Highly Robust Organometallic Small-Molecule-Based Nonvolatile Resistive Memory Controlled by a Redox-Gated Switching Mechanism

Although organic small-molecule-based memory devices (OSMDs) have been demonstrated to show great potential for the application in next-generation data-storage technology, progress toward their further development has been hugely hindered by the ambiguity of their electrical switching mechanism. Thus, purposely fabricating OSMDs with a definite switching behavior is very urgent. Here, we reported a redox-gated nonvolatile rewritable memory device using an organometallic small molecule as an active material. By introducing the redox-active ferrocene into an organic skeleton, the target small molecule exhibits reliable and robust FLASH-type bistable electrical characteristics with a clear redox-controlled switching mechanism, which leads to low operational voltages, good endurance, and long retention. Our study offers a proof-of-concept strategy to design controllable OSMDs with excellent performances.

Ferrocenyl naphthalenes: substituent- and substitution pattern-depending charge transfer studies

The synthesis and characterisation of a series of ferrocenyl-functionalized naphthalenes is reported, whereby the electrochemical behaviour and charge transfer properties depend on the substitution pattern.

Near-infrared absorbing tetracyanobutadiene-bridged diketopyrrolopyrroles

Herein we have synthesized near-infra red absorbing TCBD bridged diketopyrrolopyrroles by a [2+2] cycloaddition–retroelectrocyclization reaction in order to see the effects of end capping donors and electron-withdrawing TCBD on the optical and electrochemical properties.

Symmetrical and unsymmetrical triphenylamine based diketopyrrolopyrroles and their use as donors for solution processed bulk heterojunction organic solar cells

Two small molecules DPP3 (D–π–A) and DPP4 (D–π–A–π–D) with triphenylamine (TPA) donors and diketopyrrolopyrrole (DPP) acceptors linked with ethyne linkers were designed and synthesized by the Pd-catalyzed Sonogashira cross-coupling reaction.

Tetracyanobutadiene functionalized ferrocenyl BODIPY dyes

Tetracyanobutadiene (TCBD) derivatives of ferrocenyl BODIPYs 2a-2c were designed and synthesized by [2 + 2] cycloaddition-retroelectrocyclization reaction of tetracyanoethylene (TCNE) with meso alkynylated ferrocenyl BODIPYs. The TCBD substituted ferrocenyl BODIPYs were designed in such a way that the distance between the ferrocenyl unit and the TCBD remains constant, whereas the distance between the BODIPY and the TCBD unit varies. The TCBD and BODIPY units were connected directly through a single bond (in 2a), through a phenylacetylene linkage (in 2b) and through a vinyl linkage (in 2c). The photonic and electrochemical properties of ferrocenyl BODIPYs were strongly perturbed by the incorporation of TCBD. The TCBD derivatives 2a-2c show red shifted absorption compared to their precursors 1a-1c. The single crystal structures of TCBD functionalized ferrocenyl BODIPYs 2a and 2c reveal extensive intermolecular hydrogen bonding but lack π-π stacking interactions.

Star shaped ferrocenyl substituted triphenylamines

This manuscript reports design and synthesis of star shaped ferrocenyl substituted triphenylamine conjugates (Fc-TPA) 3a–3c by the Pd-catalyzed Sonogshira cross-coupling reaction.