Coplanar Conformation Research Articles

Aromatic Ring-Fused Amidine Based Allosteric Receptors Activated by Guest-Induced π-Conjugation Switching.

Amidine-substituted allosteric receptors 2a and 2b for benzenediols were synthesized. Receptor 2a with five-membered amidines exhibited greater allostericity than the amide-substituted receptor 1, while 2b with six-membered amidines exhibited less allostericity. NMR titration experiments revealed that a significant enthalpic factor was involved in the allostericity of these receptors. X-ray and DFT optimized structures of 2a and 2b revealed that 2a adopted a coplanar conformation with π-conjugation between the amidines and the phenylene ring of the hydrindacene framework, resulting in high allostericity due to inactivation of the initial binding.

Unusual Cross-Conjugation in Cyclic Dipeptide-Based Building Blocks for Donor-Acceptor Semiconducting Conjugated Polymers.

Cross conjugation, though prevalent in many organic compounds, is typically considered less effective for electron delocalization compared to linear conjugation. Consequently, it is rarely used as the backbone structure for semiconducting conjugated polymers. In this study, we designed and synthesized a novel building block, TIDP, which features a central cyclic dipeptide with cross conjugation characteristics. Strong intramolecular hydrogen bonding interactions confer TIDP with a highly rigid and coplanar conformation. Importantly, theoretical calculations reveal that π electrons are well delocalized across the entire structure, despite its low aromaticity. Conjugated polymers incorporating TIDP exhibit high charge carrier mobilities, demonstrating the effective π electrons delocalization of this innovative building block. Our findings show that with rational design, cross conjugation can achieve effective π electrons delocalization, providing a valuable approach for developing high-performance conjugated polymers for organic electronic materials.

Unusual Cross‐Conjugation in Cyclic Dipeptide‐Based Building Blocks for Donor–Acceptor Semiconducting Conjugated Polymers

AbstractCross conjugation, though prevalent in many organic compounds, is typically considered less effective for electron delocalization compared to linear conjugation. Consequently, it is rarely used as the backbone structure for semiconducting conjugated polymers. In this study, we designed and synthesized a novel building block, TIDP, which features a central cyclic dipeptide with cross conjugation characteristics. Strong intramolecular hydrogen bonding interactions confer TIDP with a highly rigid and coplanar conformation. Importantly, theoretical calculations reveal that π electrons are well delocalized across the entire structure, despite its low aromaticity. Conjugated polymers incorporating TIDP exhibit high charge carrier mobilities, demonstrating the effective π electrons delocalization of this innovative building block. Our findings show that with rational design, cross conjugation can achieve effective π electrons delocalization, providing a valuable approach for developing high‐performance conjugated polymers for organic electronic materials.

Enhanced Enantioselective Discrimination Regulated by Achiral Ligands in Chiral Metal-Organic Frameworks.

Enantioselective recognition is a fundamental property of chiral linkers in chiral metal-organic frameworks (CMOFs). However, clarifying the efficient enantioselective discrimination tailored by achiral linkers remains challenging to explain the chiral recognition mechanism and efficiency. Here, two CMOFs ([Zn2(l-Phe)2(bpa)2]n and [Zn2(l-Phe)2(bpe)2]n) with the completely different enantioselective recognition are synthesized from different nonchiral ligands and the same chiral ligands. The enantioselective recognition of CMOF is undoubtedly related to l-Phe, which differs in the hydrogen bonding to the Trp enantiomer. However, the electrochemical signals are weak and undifferentiated. [Zn2(l-Phe)2(bpe)2]n produces a flattened coplanar conformation with the -C═C- tether in the achiral ligand. The flattened achiral bpee ligand and its surrounding chiral phenylalanine molecules interact through multiple π-π stacking and hydrogen bonding, which together create a chiral sensor that facilitates the recognition of l-Trp. However, [Zn2(l-Phe)2(bpa)2]n produces a stepped conformation due to the -C-C- tether in the achiral ligand; despite the recognition effect of bpea, the recognition is unsatisfactory. Therefore, the chiral recognition of the two CMOFs stems from the synergistic effect between chiral and achiral ligands. This work shows that nonchiral ligands are also crucial in determining enantiomeric discrimination and opens up a new avenue for designing chiral materials.

Benzodipyrrolidone-based donor-acceptor semiconducting polymers with high hole mobility and noncovalent conformational locks

Constructing highly coplanar polymer backbone plays an important role in boosting the carrier mobility of organic field effect transistors (OFETs) devices. In this study, based on noncovalent conformational locks strategy, we synthesized the electron-acceptor (A) monomer via introducing 3-dodecylthiophene on strong electron-deficient planar benzodipyrrolidone and the electron-donor (D) monomers containing different numbers (0–2) of fluorine atoms at different positon. A series of novel D-A copolymers, namely PBDP-F0, PBDP-F1 and PBDP-F2 with different backbone conformational locks through F⋯S and F⋯H–C noncovalent interactions, were obtained via Stille polycondensation. For the application in an organic field-effect transistor, all the polymers exhibited p-type charge transport characteristics and good performance with the highest hole mobilities as 0.24 cm2 V−1 s−1 for PBDP-F0, 0.87 cm2 V−1 s−1 for PBDP-F1 and 1.93 cm2 V−1 s−1 for PBDP-F2, respectively. AFM and GIXRD investigations indicated that all polymers take predominantly edge-on orientation packing mode because of the rigid and coplanar backbone conformation and the annealing films exhibited small π-π stacking distances of 3.73, 3.71 and 3.69 Å for PBDP-F0, PBDP-F1 and PBDP-F2 respectively. This work demonstrates that modified BDP-based D-A copolymers with conformational locks has a potential application in the high-performance semiconductor materials.

J-Aggregate Promoting NIR-II Emission for Fluorescence/Photoacoustic Imaging-Guided Phototherapy.

J-aggregate is a promising strategy to enhance second near-infrared window (NIR-II) emission, while the controlled synthesis of J-aggregated NIR-II dyes is a huge challenge because of the lack of molecular design principle. Herein, bulk spiro[fluorene-9,9'-xanthene] functionalized benzobisthiadiazole-based NIR-II dyes (named BSFX-BBT and OSFX-BBT) are synthesized with different alkyl chains. The weak repulsion interaction between the donor and acceptor units and the S…N secondary interactions make the dyes to adopt a co-planar molecular conformation and display a peak absorption >880nm in solution. Importantly, BSFX-BBT can form a desiring J-aggregate in the condensed state, and femtosecond transient absorption spectra reveal that the excited states of J-aggregate are the radiative states, and J-aggregate can facilitate stimulated emission. Consequently, the J-aggregated nanoparticles (NPs) display a peak emission at 1124nm with a high relative quantum yield of 0.81%. The efficient NIR-II emission, good photothermal effect, and biocompatibility make the J-aggregated NPs demonstrate efficient antitumor efficacy via fluorescence/photoacoustic imaging-guided phototherapy. The paradigm illustrates that tuning the aggregate states of NIR-II dye via spiro-functionalized strategy is an effective approach to enhance photo-theranostic performance.

Manipulating electron linking units and side chains for high-performance all-polymer photodetectors with stability over 5000 h

All-polymer photovoltaic devices have attracted extensive attention for their promising applications in various flexible devices. Although abundant polymer donors with superior properties are developed, new polymer acceptors are urgently required to optimize or update the performances of the devices. Herein, three novel polymer acceptors, namely PY-DTT, PY-DTP-C, and PY-DTP-Ph, based on dithienothiophene (DTT) and dithienopyrrole (DTP) with alkyl and aryl side chains as the linking units respectively are synthesized and employed in the all-polymer photodetectors (all-PPDs). The PY-DTP-Ph shows broader absorption, stronger intermolecular interaction, and more coplanar molecular conformation compared with the other two acceptors. Blending with donor PM6, the PY-DTP-Ph based all-PPDs exhibit maximum responsivity of 292.1 mA W−1 and specific detectivity of 5.4 × 1013 cm Hz1/2 W−1 at a bias of −0.1 V. Furthermore, the device achieves fast response speed (τr/τf = 1.2/21.8 μs) and a large linear dynamic range of 105.0 dB. Intriguingly, the photodetectors present extraordinary air stability for 5000 h, attributing to the ideal miscibility and morphology of the blend films. These results demonstrate close relationships between the electron linking units, side chains and the basic properties of polymer acceptors, which in turn affects the performances of the photodetector devices.

Chiral Diketopyrrolopyrrole-Based Conjugated Polymers with Intramolecular Rotation-Isomeric Conformation Asymmetry for Near-Infrared Circularly Polarized Light-Sensing Organic Phototransistors.

Recent advances in chiral nanomaterials interacting with circularly polarized (CP) light open new expectations for optoelectronics in various research fields such as quantum- and biology-related technology. To fully utilize the great potential of chiral optoelectronic devices, the development of chiral optoelectronic devices that function in the near-infrared (NIR) region is required. Herein, we demonstrate a NIR-absorbing, chiroptical, low-band-gap polymer semiconductor for high-performance NIR CP light phototransistors. A newly synthesized diketopyrrolopyrrole-based donor-acceptor-type chiral π-conjugated polymer with an asymmetric alkyl side chain exhibits strong chiroptical activity in a wavelength range of 700-1000 nm. We found that the attachment of an enantiomerically pure stereogenic alkyl substituent to the π-conjugated chromophore backbone led to strong chiroptical activity through symmetry breaking of the π-conjugation of the backbone in a molecular rotational motion while maintaining the coplanar backbone conformation for efficient charge transport. The NIR CP light-sensing phototransistors based on a chiral π-conjugated polymer photoactive single channel layer exhibit a high photoresponsivity of 26 A W-1 under NIR CP light irradiation at 920 nm, leading to excellent NIR CP light distinguishability. This study will provide a rationale and strategy for designing chiral π-conjugated polymers for high-performance NIR chiral optoelectronics.

Benzotriazole-based copolymers with an interlocked conformation for mitigating the correlation of thermoelectric parameters

As for thermoelectric materials, a strong trade-off relationship between the electrical conductivity (σ) and the Seebeck coefficient (S) is a huge obstacle to maximization of their thermoelectric (TE) performances, especially for polymeric semiconductors with a single component. Recently, some of intensive efforts were made to explore effective methods for decoupling TE parameters of organic semiconductors. In this work, a novel type of D–A non-fused-ring copolymers were designed and synthesized from the Stille coupling polymerization of cyclopentadithiophene and benzotriazole units (fluorinated or non-fluorinated). The incorporation of fluorine atoms into the polymer backbone constructed skillfully a fully interlocked coplanar conformation via the dual assistance of the F···S and N···H noncovalent interactions, significantly enhancing the ordered degree of molecular stacking and thus the σ and S values. More importantly, the two polymers achieved a simultaneous increase in both the σ and S within a certain doping time, probably due to that the bimodal orientation of polymers played a crucial role in decoupling the correlation between σ and S. Consequently, FeCl3-doped P(CPD-BTA-2F) harvested an optimal power factor of 7.77 ± 0.77 μW m−1 K−2, which is one order of magnitude higher than that of P(CPD-BTA). This work, albeit only a modest power factor (PF) was attained, offered a valuable insight into the molecular engineering for breaking through the trade-off relationship between σ and S, and shed some light on the development of promising polymeric TE materials.

Coplanar Conformational Structure of π-Conjugated Polymers for Optoelectronic Applications.

Hierarchical structure of conjugated polymers is critical to dominating their optoelectronic properties and applications. Compared to nonplanar conformational segments, coplanar conformational segments of conjugated polymers (CPs) demonstrate favorable properties for applications as a semiconductor. Herein, recent developments in the coplanar conformational structure of CPs for optoelectronic devices are summarized. First, this review comprehensively summarizes the unique properties of planar conformational structures. Second, the characteristics of the coplanar conformation in terms of optoelectrical properties and other polymer physics characteristics are emphasized. Five primary characterization methods for investigating the complanate backbone structures are illustrated, providing a systematical toolbox for studying this specific conformation. Third, internal and external conditions for inducing the coplanar conformational structure are presented, offering guidelines for designing this conformation. Fourth, the optoelectronic applications of this segment, such as light-emitting diodes, solar cells, and field-effect transistors, are briefly summarized. Finally, a conclusion and outlook for the coplanar conformational segment regarding molecular design and applications are provided.

A Rising Star: Luminescent Carbene-Metal-Amide Complexes.

Coinage metal (gold, silver, and copper) complexes are attractive candidates to substitute the widely studied noble metal complexes, such as, iridium(III) and platinum(II), as luminescent materials in organic light-emitting diodes (OLEDs). However, the development of coinage metal complexes exhibiting high emission quantum yields and short exciton lifetimes is still a formidable challenge. In the past few years, coinage metal complexes featuring a carbene-metal-amide (CMA) motif have emerged as a new class of luminescent materials in OLEDs. Thanks to the coinage metal-bridged linear geometry, coplanar conformation, and the formation of excited states with dominant ligand-to-ligand charge transfer character and reduced metal d-orbital participation, most CMA complexes have high radiative rates via thermally activated delayed fluorescence. Currently, the family of CMA complexes have rapidly evolved and remarkable progresses in CMA-based OLEDs have been made. Here, a Concept article on CMA complexes is presented, with a focus on molecular design principles, the correlation between molecular structure/conformation and optoelectronic properties, as well as OLED performance. The future prospects of CMA complexes are also discussed.

The design, synthesis, and inhibition of Clostridioides difficile spore germination by acyclic and bicyclic tertiary amide analogs of cholate

Clostridioides difficile infection (CDI) is a major identifiable cause of antibiotic-associated diarrhea. In our previous study (J. Med. Chem., 2018, 61, 6759–6778), we have identified N-phenyl-cholan-24-amide as a potent inhibitor of spore germination. The most potent compounds in our previous work are N-arylamides. We were interested in the role that the conformation of the amide plays in activity. Previous research has shown that secondary N-arylamides exist exclusively in the coplanar trans conformation while tertiary N-methyl-N-arylamides exist in a non-planar, cis conformation. The N-methyl-N-phenyl-cholan-24-amide was 17-fold less active compared to the parent compounds suggesting the importance of the orientation of the phenyl ring. To lock the phenyl ring into a trans conformation, cyclic tertiary amides were prepared. Indoline and quinoline cholan-24-amides were both inhibitors of spore germination; however, the indoline analogs were most potent. Isoindoline and isoquinoline amides were inactive. We found that the simple indoline derivative gave an IC50 value of 1 μM, while the 5′-fluoro-substituted compound (5d) possessed an IC50 of 400 nM. To our knowledge, 5d is the most potent known spore germination inhibitor described to date. Taken together, our results indicate that the trans, coplanar conformation of the phenyl ring is required for potent inhibition.

Binary all-polymer solar cells with efficiency over 17% by fine-tuning halogenated thiophene linkers of polymer acceptors

All-polymer solar cells (APSCs) have achieved significant advances because of the rising of polymerized small molecular acceptors (PSMAs). While, the effect of halogen atoms on PSMAs in linkers has not been systematically studied. Herein, three PSMAs of PZC1, PZC2, and PZC3 are designed and synthesized by introducing fluorine and chlorine atom on the linkers to fine-tune their optoelectronic and molecular packing properties. Both halogenated polymer acceptors exhibit a slightly blue-shifted absorption range as well as deeper-lying frontier energy levels. When compared with non-halogenated PZC1, the fluorinated polymer acceptor (PZC2) presents better co-planar and rigid molecular conformation. The 3,4-dichlorothiophene-based polymer acceptor (PZC3) displays a distinctly twisted molecular chain between terminal groups and 3,4-dichlorothiophene owing to the steric hindrance between chlorine (Cl) and hydrogen (H) atoms. Due to the optimal morphologies in PM6:PZC2 film, the corresponding devices exhibit an excellent PCE of 17.30%, superior to those of PM6:PZC1 (13.83%) and PM6:PZC3 (15.75%) based devices. The mechanical robustness of three blend films is further investigated. PZC2-based films exhibit outstanding mechanical flexibility. Afterwards, the PM6:PZC2-based flexible devices achieve a PCE of 14.24%. Our results demonstrate that the usage of halogenated thiophene offers a practical way to fine-tune the performance of APSCs.

Stable Deep‐Blue Electroluminescence from Hierarchical Crystalline Structure Based on Planar Conformational Terfluorenes: Benefits of Preventing Defect Structures Formation

AbstractLiner‐type organic conjugated molecules with 1D π‐electron delocalization present conformation‐dependent intramolecular optoelectronic behavior. Significantly different from non‐planar ones, the coplanar conformational backbone of π‐conjugated molecules can enhance intramolecular π‐electron delocalization and dominate intermolecular π‐electron coupling, which are the fundamental parameters for improving their optoelectronic properties. Herein, the effect of the formation of coplanar conformation on intermolecular packing and optoelectrical properties of liner‐type steric terfluorene (DSFX‐SFSO) toward solution‐processed deep‐blue organic light‐emitting diodes (OLEDs) is systematically demonstrated. Firstly, uniform and continuous crystalline films based on the planar conformational DSFX‐SFSO molecules are achieved via thermal annealing at 160 °C, which can avoid microscale crystallization processing. Contrary to amorphous ones, these hierarchical crystalline films present robust deep‐blue emission with an efficiency of > 60%, due to the suppression of defect structures. More interestingly, this hierarchical crystalline film has a stable and efficient deep‐blue electroluminescence (CIE: 0.15, 0.09) without the obvious defective green‐band emission, even at 500 mA cm−2, also further confirming the excellent and perfect molecular landscape to obtain single‐chromophore excitonic behavior from single planar‐terfluorene segments. Therefore, obtaining a uniform hierarchical structure based on planar conformational molecules is an effective strategy to optimize the optoelectrical properties for optoelectronic applications.

Theoretical studies on thermally activated delayed fluorescence of "carbene-metal-amide" Cu and Au complexes: geometric structures, excitation characters, and mechanisms.

"Carbene-metal(I)-amide" (CMA) complexes have garnered significant attention due to their remarkable properties and potential TADF applications in organic electronics. However, the atomistic working mechanism is still elusive. Herein, we chose two CMA complexes, i.e., cyclic (alkyl)(amino) carbene-copper[gold](I)-carbazole (CAAC-Cu[Au]-Cz), and employed both DFT and TD-DFT methods, in combination with radiative and nonradiative rate calculations, to investigate geometric and electronic structures of these two complexes in the ground and excited states, including orbital compositions, electronic transitions, absorption and emission spectra, and the luminescence mechanism. It is found that the coplanar or perpendicular conformations are coexistent in the ground state (S0), the lowest excited singlet state (S1), and the triplet state (T1). Both the coplanar and perpendicular S1 and T1 states have similar ligand-to-ligand charge transfer (LLCT) character between CAAC and Cz, and some charge-transfer character between metal atoms and ligands, which is beneficial to minimize the singlet-triplet energy gaps (ΔEST) and increase the spin-orbit coupling (SOC). An interesting three-state (S0, S1, T1) model involving two regions (coplanar and perpendicular) is proposed to rationalize the experimental TADF phenomena in the CMA complexes. In addition to the coplanar ones, the perpendicular S1 and T1 states also play a role in promoting the repopulation of the coplanar S1 exciton, which is a primary source for the delayed fluorescence.

Methoxy substituent facilitated wide solvatofluorochromism, white light emission, polymorphism and stimuli-responsive fluorescence switching in donor-π-acceptor

Introducing methoxy substituent into triphenylamine-acetophenone based donor-π-acceptor fluorophore, 3-(4-(diphenylamino)phenyl)-1-phenylprop-2-en-1-one (1), produced strong solvatofluorochromism including white light emission, fluorescent polymorphs and mechano-responsive fluorescence switching. The unsubstituted and methoxy substituted compounds displayed strong solvent polarity mediated tunable emission in the solution. Interestingly, 3-(4-(diphenylamino)phenyl)-1-(4-methoxyphenyl)prop-2-en-1-one (2) and 3-(4-(diphenylamino)-2-methoxyphenyl)-1-(4-methoxyphenyl)prop-2-en-1-one (3) showed single molecule white light emission in DMSO and ethanol, respectively. 1-3 exhibited strong green/yellow fluorescence in the solid-state (Quantum yield (Φf) = 10 to 23%). 2 produced fluorescent polymorphs (green (2-G) and yellow (2-Y). Single crystal structural analysis revealed that donor and acceptor phenyl units adopted coplanar conformation in 2-G and 3 whereas twisted molecular conformation in 1 and 2-Y. Further, 2-G exhibited π…π interactions facilitated isolated dimers whereas 2-Y showed well separated molecules in the crystal lattice. Aggregation induced emission (AIE) studies showed morphological transformation induced fluorescence tuning for 2. The intramolecular charge transfer (ICT) from TPA to acetophenone was confirmed by computational studies. Mechanofluorochromic (MFC) studies of 1 showed only slight reduction of intensity without modulating fluorescence wavelength significantly but 2 and 3 exhibited visible emissive colour change from yellow to green and vice versa by crushing and heating. Both 2 and 3 also exhibited self-reversible fluorescence switching that was confirmed by PXRD pattern. Thus, methoxy group introduction resulted in obtaining white light emitting fluorescence molecules in the solution state and self-reversible fluorescence switching materials.

Investigation of performance and efficiency of donor-π-bridge-acceptor based material solar cell

• Structural modification influence of triphenyleamine-based dyes. • Incorporation of an electro-withdrawing unit improve the intramolecular charge transfer. • Investigated TPA-III scaffolds are expected to show higher red shift. The novel groups of organic chromophores containing triphenylamine (TPA) (ATP-I to ATP-IV) have been constructed by structural modification of electron donors with substitution biphenyl and bipyridine rings inserting a π-linkage. Density functional theory (DFT) and time-dependent type of it (TD-DFT) have been operated to study results of donating ability of TPA and spacer on absorption, geometrical, photovoltaic, and energetic attributes of these sensitizers. Structural attributes have been revealed that incorporation of TPA, acceptor and π bridge include a perfect coplanar conformation in TPA-III. Based on frequency computations and ground-state optimization, bandgap (E g ) energy, E LUMO , E HOMO have been determined. For enlightening maximum absorbance wavelength (λ max ) and oscillator strength (f), TD-CAM-B3LYP computations have been employed. The absorption wavelength was shifted about ∼650 nm for TPA-III. Results indicate that among all dyes, TPA-III dye is considered the most promising candidates.

Beyond "Mega": Origin of the "Giga" Stokes Shift for Triazolopyridiniums.

Over the past decade, fluorophores that exhibit "mega" Stokes shifts, defined to be Stokes shifts of greater than 100 nm, have gained considerable attention due to their potential technological applications. A subset of these fluorophores have Stokes shifts of at least 10,000 cm-1, for whom we suggest the moniker "giga" Stokes shift. The majority of "giga" Stokes shifts reported in the literature arise from the twisted intramolecular charge transfer mechanism, but this mechanism does not fit empirical characterization of triazolopyridinium (TOP). This observation inspired a density functional theory (DFT) and time-dependent DFT study of TOP, and several related fluorophores, to elucidate the novel photophysical origin for the "giga" Stokes shift of TOP. The resulting computational models revealed that photoexcitation of TOP yields a zwitterionic excited state that undergoes significant structural relaxation prior to emission. Most notably, TOP has two orthogonal moieties in the ground state that adopt a coplanar geometry in the excited state. According to Hückel's rule, both the heterocycle and phenyl moieties of TOP should be aromatic in an orthogonal ground state. However, according to Baird's rule, these individual moieties should be anti-aromatic in the excited state. By relaxing to a coplanar conformation in the excited state, TOP likely forms a single aromatic system consisting of both the heterocycle and phenyl moieties.

Design new D-π-A materials for sensitizers for dye-sensitized solar cells: Quantum chemical study

Within this paper, we developed a new series of organic chromophores based on triphenyleamine (TPA) (AL1, AL-2, AL-11 and AL-22) by engineering the structure of the electron donor (D) unit via replacing a phenyle ring or inserting thiophene as a π-linkage. For the sake of scrutinizing the impact of the TPA donating ability and the spacer upon the photovoltaic, absorptional, energetic, and geometrical characteristic of these sensitizers, density functional theory (DFT) and time-dependent DFT (TD-DFT) have been utilized. According to structural characteristics, incorporating the acceptor, π-bridge and TPA does not result in a perfect coplanar conformation in AL-22. We computed EHOMO, ELUMO and bandgap (Eg) energies by performing frequency and ground-state calculations. Next, we performed TD-CAM-B3LYP calculations to compute oscillator strength (f) and the maximum adsorption wavelength (λmax). The absorption bands were extended up to ∼ 647 nm for AL-22. The findings demonstrated that AL-22 is the most promising dye among other dyes.

Synthesis, spectroscopic characterization, one and two-photon absorption properties of β-β linked BODIPY dimers

Five β-β linked BODIPY dimers (d1-d5) with different electron-donating/withdrawing groups at the meso-position were synthesized through improved synthetic methods. All compounds were characterized by 1H and 13C NMR and HRMS. The single crystal X-ray analyses indicate that d4 and d5 display a linear coplanar conformation with two linked BODIPY moiety. Their photophysical and electrochemical properties have been investigated by UV–vis absorption spectroscopy, steady-state and time-resolved fluorescence spectroscopy, two-photon excited spectroscopy and cyclic voltammetry. The β-β linked BODIPY dimers exhibit a prominent red shift from the visible region to the red/near-infrared region of their absorption and emission spectra, large Stokes shifts and moderate two-photon absorption cross section σ2 with different groups at the meso-position.