Tuning of the HOMO-LUMO Gap of Symmetrical and Unsymmetrical Ferrocenyl-Substituted Diketopyrrolopyrroles

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.

Synthesis, Structure, and Significant Energy Gap Modulation of Symmetrical Silafluorene-Cored Tetracyanobutadiene and Tetracyanoquinodimethane Derivatives

A series of symmetrical tetracyanobutadiene and tetracyanoquinodimethane derivatives with a D-A-D'-A-D structural configuration and silafluorene core (D') were designed and readily synthesized via a [2+2] cycloaddition-retroelectrocyclization (CA-RE) reaction. We found that the photophysical properties and HOMO and LUMO energy levels and gaps of the silafluorene derivatives could be profoundly remolded through CA-RE reactions and modulated by varying the peripheral donor units from phenyl, m-dimethoxyphenyl, and N,N-dimethylaniline to triphenylamine groups. After CA-RE reactions, the HOMO-LUMO gaps of 1a-1j are in the range of 1.75-2.78 eV, with significant decreases of 0.52-1.46 eV compared to those of the parent silafluorene compounds 2a-2j. The intriguing crystal structures of 1f and 1j were analyzed and elucidated to show their unique potential porosity. The stability, electrochemical, and computational studies were systematically performed to unveil the reshaped electron-donating and -withdrawing nature in one molecular system. 1h-1j with peripherally strong amino donors exhibit an intense and broad intramolecular charge transfer absorption band in the near-infrared region from 550 to 900 nm. The molecular design and synthesis reported here broaden the types and fields of D-A molecular systems for potential applications in organic optoelectronic devices.

Photoinduced Charge Separation Prompted Intervalence Charge Transfer in a Bis(thienyl)diketopyrrolopyrrole Bridged Donor-TCBD Push-Pull System

Intervalence charge transfer (IVCT), a phenomenon observed in molecular systems comprised of two redox centers differing in oxidation states by one unit, is reported in a novel, newly synthesized, multi-modular donor-acceptor system comprised of central bis(thienyl)diketopyrrolopyrrole (TDPP) hosting two phenothiazine-tetracyanobutadiene (PTZ-TCBD) entities on the opposite sides. One-electron reduction of TCBD promoted electron exchange between the two TCBD resulting in IVCT transition in the near-infrared region. The stabilization energy, -ΔG_com and comproportionation equilibrium constant, K_com calculated from peak potentials of the split reduction waves were found to be 1.06×10⁴  J mol^-1 , and 72.3 M^-1 , respectively. Further, the IVCT transition was also witnessed during the process of thermodynamically feasible electron transfer upon excitation of the TDPP entity in the system, and served as a diagnostic marker to characterize the electron transfer product. Subsequent transient absorption spectral studies and data analysis by Global and Target analyses revealed occurrence of ultrafast charge separation (k_cs ≈10¹⁰  s^-1 ) owing to the close proximity and good communication between the entities of the multi-modular donor-acceptor system. The role of central TDPP in promoting IVCT is borne out from the present investigation.

Columnar Mesomorphism of Board-Shaped Perylene, Diketopyrrolopyrrole, Isoindigo, Indigo, and Quinoxalino-Phenanthrophenazine Dyes

The properties of organic dyes depend as much on their intermolecular interactions as on their molecular structure. While it is generally predictable what supramolecular structure would be ideal for a specific application, the generation of specific supramolecular structures by molecular design and suitable processing methods remains to be a challenge. A versatile approach to different supramolecular structures has been the application of mesomorphism in conjunction with alignment techniques and self-assembly at interfaces. Reviewed here is the columnar mesomorphism of board-shaped dyes perylene, indigo, isoindigo, diketopyrrolopyrrole, and quinoxalinophenanthrophenazine. They generate a larger number of different supramolecular structures than conventional disc-shaped (discotic) mesogens because of their non-circular shape and directional intermolecular interactions. The mesomorphism of all but the perylene derivatives is systematically and comprehensively covered for the first time.

Metal Functionalized Diketopyrrolopyrroles: A Promising Class of Materials for Optoelectronic Applications

After first report on diketopyrrolopyrrole in 1974 by Farnum et al., a wide variety of its derivatives have been reported for material and biological applications. In this review we discuss various design strategies used for the synthesis of metal functionalized diketopyrrolopyrrole derivatives along with their photophysical and electrochemical studies with respect to material and biological applications. Some exciting applications of ferrocenyl functionalized diketopyrrolopyrrole derivatives such as non-linear optics, organic solar cells and photothermal therapy were recently reported, which are also discussed in this review.

Fine-tuning the optoelectronic chattels of fluoreno-thiophene centred molecular semiconductors through symmetric and asymmetric push–pull switch

Optoelectronic properties of symmetrical and unsymmetrical fluoreno-thienyl π-semiconductors were studied.

Diketopyrrolopyrrole-Based and Tetracyano-Bridged Small Molecules for Bulk Heterojunction Organic Solar Cells

Research on bulk heterojunction organic solar cells has rapidly grown over the past two decades, and device performance has reached power conversion efficiencies over 13 %. In this focus review, we highlight design strategies used for the development of diketopyrrolopyrrole- and tetracyano-based molecular donors. We also describe how tetracyano-bridged non-fullerene acceptors can be developed by a click-type [2+2]-cycloaddition-electrocyclic ring-opening reaction of acetylene-bridged small molecules with tetracyanoethylene by simple modification.

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.

NIR-Absorbing Donor-Acceptor Based 1,1,4,4-Tetracyanobuta-1,3-Diene (TCBD)- and Cyclohexa-2,5-Diene-1,4-Ylidene-Expanded TCBD-Substituted Ferrocenyl Phenothiazines

A series of unsymmetrical (D-A-D₁ , D₁ -π-D-A-D₁ , and D₁ -A₁ -D-A₂ -D₁ ; A=acceptor, D=donor) and symmetrical (D₁ -A-D-A-D₁ ) phenothiazines (4 b, 4 c, 4 c', 5 b, 5 c, 5 d, 5 d', 5 e, 5 e', 5 f, and 5 f') were designed and synthesized by a [2+2] cycloaddition-electrocyclic ring-opening reaction of ferrocenyl-substituted phenothiazines with tetracyanoethylene (TCNE) and 7,7,8,8-tetracyanoquinodimethane (TCNQ). The photophysical, electrochemical, and computational studies show a strong charge-transfer (CT) interaction in the phenothiazine derivatives that can be tuned by varying the number of TCNE/TCNQ acceptors. Phenothiazines 4 b, 4 c, 4 c', 5 b, 5 c, 5 d, 5 d', 5 e, 5 e', 5 f and 5 f' show redshifted absorption in the λ=400 to 900 nm region, as a result of a low HOMO-LUMO gap, which is supported by TD-DFT calculations. The electrochemical study exhibits reduction waves at low potential due to strong 1,1,4,4-tetracyanobuta-1,3-diene (TCBD) and cyclohexa-2,5-diene-1,4-ylidene-expanded TCBD acceptors. The incorporation of cyclohexa-2,5-diene-1,4-ylidene-expanded TCBD stabilized the LUMO energy level to a greater extent than TCBD.

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.

D–A–D–π–D–A–D type diketopyrrolopyrrole based small molecule electron donors for bulk heterojunction organic solar cells

Two organic small molecules based on diketopyrrolopyrrole (DPP) units having a D–A–D–π–D–A–D structure denoted as DPP-DPP and DPPTDPP were synthesized.

Small molecule based N-phenyl carbazole substituted diketopyrrolopyrroles as donors for solution-processed bulk heterojunction organic solar cells

We report two acetylene-bridged small molecules DPP5 and DPP6 with low HOMO–LUMO gaps as donors along with PC₇₁BM as an acceptor for the fabrication of solution-processed bulk heterojunction solar cells.