A nine-ring fused terrylene diimide exhibits switching between red TADF and near-IR room temperature phosphorescence.

Herein, we report the first example of a terrylene diimide derivative that switches emission between thermally activated delayed fluorescence (TADF) and room temperature phosphorescence (RTP) in the red region. By design, the molecule TDI-cDBT boasts a symmetrical, consecutively fused nine-ring motif with a kite-like structure. The rigid core formed by the annulated dibenzothiophene moiety favoured efficient intersystem crossing and yielded a narrow-band emission with a full-width half maxima (FWHM) of 0.09 eV, along with high colour purity. A small ΔE S1-T1 of 0.04 eV facilitated thermally activated delayed fluorescence, enhancing the quantum yield to 88% in the red region. Additionally, it also prefers a direct triplet emission from the aggregated state. The room temperature phosphorescence observed from the aggregates has a longer emission lifetime of 1.8 ms, which is further prolonged to 8 ms at 77 K in the NIR region. Thus, the current strategy is successful in not only reducing ΔE S1-T1 to favour TADF but also serves as a novel platform that can switch emission from TADF to RTP depending upon the concentration.

A Bis-Porphyrin Cavitand Breathing-In to Constrict Bucky Balls.

Bis-porphyrin cages have long been exploited to bind fullerenes selectively for various applications. The major consideration for an effective binding here had been the cavity size. Herein, we structurally demonstrate that a bis-Ni-porphyrin cavitand having even a smaller cavity can host a larger fullerene by a breathing and ruffling mechanism. It has also been shown that both the electronic and steric influence at the meso- positions of the porphyrin in fact dictate the binding character. The smaller cavity of 2NiD exhibits preferential binding for C70 over C60; however, surprisingly, the larger cavities in 2HD and 2NiTD display stronger affinities for C60 over the larger fullerene. We show here that the structural elasticity infused both by the metalloporphyrins and the connecting bridges play a major role in directing the binding. These conclusions have adequately been supported by structural and spectroscopic investigations. Additionally, the suitability of one of the conjugates for photoinduced charge-separation has been investigated using ultrafast transient absorption measurements. 2NiD⊃C60 has a charge separation timescale of ~0.8 ps, while charge recombination occurs at a longer timescale of ~920 ps.

The deeper it goes, the brighter it glows: NIR emissive nitro-terrylene diimides with deep LUMOs.

Herein, we present the first examples of air-stable, deep-lowest unoccupied molecular orbital (LUMO) polycyclic aromatic molecules with emission in the near-infrared (NIR) region, using nitration as a strategy. Despite the fact that nitroaromatics are non-emissive, the choice of a comparatively electron-rich terrylene core proved to be beneficial for achieving fluorescence in these molecules. The extent of nitration proportionately stabilized the LUMOs. Tetra-nitrated terrylene diimide exhibited a deep-LUMO (≤-4.5 eV) of -5.0 eV vs. Fc/Fc+, the lowest for any larger RDIs. These are also the only examples of emissive nitro-RDIs, with larger quantum yields.

Bridging the Bays, Both Ways: A Janus Butterfly-Shaped Intense NIR-Emitting Terrylene Diimide.

Molecules with intense near-IR (NIR) emission are beneficial for modern applications such as night vision, bio-imaging etc. However, elaborate synthetic manipulations make them demanding to accomplish. Herein, we present a simple yet exciting strategy to obtain novel Janus butterfly-shaped terrylene diimide derivatives with carbazole wings having absorption and intense emission in the NIR. Especially, unsymmetrically substituted terrylene diimides (TDIs) have been observed to have impressive emission quantum yields (up to 93 %), highest for this class of compounds. Minimal structural distortion as evidenced from structural characterization has been shown to correlate with these observations. Also, a novel two-tiered TDI-carbazole having an intense emission at 897 nm is also reported. Our strategy demonstrates that efficient near-IR luminophores can be achieved via precise functionalization.

Isolation and Structural Characterization of Regioisomers of Dibrominated Terrylene Diimides.

Diverse applications of rylenediimides are attributed to the accessibility of simple methodologies to obtain versatile halogenated precursors. Terrylene diimides are important molecular platforms to achieve materials with NIR absorption and emission. In this work, we present a simple synthesis for the hitherto unknown di- and tribromo-TDIs. Regioisomerically pure dibromo TDIs, including an elusive 1,14-derivative, could be successfully isolated and structurally characterized along with tribromo-TDI. The utility of these bromo derivatives has also been demonstrated with a redox anchoring.

A tris-(manganese(iii))corrole-porphyrin-corrole triad: synthesis, characterization and catalytic epoxidation.

A homotrimetallic manganese(iii) corrole-porphyrin-corrole triad has been synthesized and structurally characterized. Corrole and porphyrin rings in the free base corrole-porphyrin-corrole triad are found to be roughly perpendicular to each other having a dihedral angle of 83° in the solid state. A dihedral angle of nearly 67° was found between Mn(iii)-corroles and Mn(iii)-porphyrin rings in the manganese triad complex, 1-Mn. The absorption spectrum of the manganese triad was observed to be the sum of the absorptions from manganese corrole and manganese porphyrin. The catalytic activity of the manganese triad complex was investigated for the epoxidation of styrene using iodobenzene diacetate as an oxygen source. Preliminary results obtained showed the superior activity of the manganese triad as an oxidation catalyst as compared to the respective monomer catalysts. Moreover, product yield in the oxidation of styrene catalyzed by the manganese triad was found to be higher than that of the combined activity of both monomers taken in same equivalence. The reason behind this higher yield may be attributed to an increased local concentration of the catalytic centers at the reaction site.

A cell-permeant small molecule for the super-resolution imaging of the endoplasmic reticulum in live cells.

The endoplasmic reticulum (ER) constitutes about half of the total membrane of a eukaryotic cell, and defects in the ER have been shown to be linked with a variety of diseases. To investigate these underlying mechanisms in detail, the specific labelling of the ER for high-resolution long-term live-imaging can serve as an important tool. Here, we report the identification of a stimulated emission depletion (STED) microscopy-compatible BODIPY derivative (NH2-BODIPY) to selectively image the ER. In contrast to the conventional ER-Tracker™ dye, NH2-BODIPY selectively labels the ER at a much lower concentration with no detectable cytotoxicity. Conventional imaging agents are often unstable under the intense light field used for STED microscopy, but NH2-BODIPY is stable due to its robust structure and therefore it has the potential to be widely exploited for ER imaging.

Corrole-BODIPY Dyad as Small-Molecule Donor for Bulk Heterojunction Solar Cells.

Dyes based on charge-transfer (CT) characteristics are attractive candidates for organic photovoltaics due to their intense and broad absorption window. In these molecular frameworks, electron-rich donors and electron-deficient acceptors are covalently linked to achieve an effective CT process. Corrole, a tetrapyrrolic congener of porphyrin, is an excellent example of an electron-rich molecule with a large molar extinction coefficient. BODIPY, on the other hand, is a well-known electron-deficient bypyrrolic boron difluoride complex with intense absorption complementary to the corrole. A combination of these two structural motifs should result in a dyad having a wide absorption window, which will be suitable for organic photovoltaics. Herein, a corrole derivative has been envisaged as an efficient donor for solution-processed bulk heterojunction solar cells with PC71BM as an acceptor for the first time. The current molecule exhibits broad absorption in the visible range in solution as well as in thin films, with a high molar extinction coefficient and a low band gap of 1.79 eV. Frontier molecular orbital energy levels were found to be complementary to those of the well-known acceptor PC71BM. The optimized devices based on Cor-BODIPY:PC71BM showed a high power conversion efficiency (PCE) of 6.6% with Jsc = 11.46 mA/cm2, Voc = 0.90 V, and FF = 0.61. A remarkable value of incident photon-to-current conversion efficiency (IPCE) of 61% has also been observed.

Metal-free Annulation at the Ortho- and Bay-Positions of Perylene Bisimide Leading to Lateral π-Extension with Strong NIR Absorption.

A novel ortho/ bay annulation reaction of perylene bisimide (PBI) has been explored in a single step synthetic procedure using perylene bisimide 1 and 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) in the absence of any metal catalyst. The single crystal solid-state X-ray diffraction structure showed a distorted framework of DBU-fused PBI 2. Compound 2 exhibited intense near-infrared absorption up to 950 nm. Reversible protonation and deprotonation accompany drastic changes in the photophysical characteristics. Further, the reaction of perylene biscarboxyanhydride with DBU offered a caprolactam ring-substituted perylene bisimide 3.

Selective Imaging of Lipids in Adipocytes by Using an Imidazolyl Derivative of Perylene Bisimide.

A small molecule, perylene bisimide imidazolyl derivative (PBI-ID), has been identified and developed as a specific marker for labelling multifunctional fat bodies in various organisms, including Drosophila and mammalian adipocytes. Interestingly, PBI-ID neither labels the plasma membranes nor cell nuclei by trapping into it. A remarkable feature of unbound PBI-ID is diminished fluorescence, which reduces the background emission noise, while contrasting the bound state effectively.

The Curious Case of a Parasitic Twin of the Corroles.

An expanded porphyrinoid has been obtained by a simple ring expansion from a contracted porphyrinoid, namely corrole. Spectroscopic, structural, and computational investigations reveal peculiar π-conjugation and geometry. The effect of extended π-conjugation is evident from perturbed redox behavior and photophysical properties. Owing to the strong diatropic ring current of the corrole and cross-conjugation, the molecule exhibits a non-aromatic nature for the expanded π-circuit, as evident from NMR studies.

Evidence for a [17] π-Electronic Full-Fledged Non-innocent Gallium(III)-Corrole Radical.

One-electron oxidation of a GaIII -corrole with N(4-BrC6 H4 )3 SbCl6 resulted in an air-stable non-innocent GaIII -corrole radical. The single-crystal X-ray crystallography of the 2,17-bis-formyl-5,10,15-tris(pentafluorophenyl)corrolato gallium(III)(chloride) radical ([3-Cl]. ) revealed delocalization of the unpaired electron, which was further confirmed by electron spin resonance (ESR) spectroscopy and spin density distribution plot. In addition, the nucleus-independent chemical shift (NICS), anisotropy-induced current density (AICD) and harmonic oscillator model of aromaticity (HOMA) supported a [17] π-electron-conjugated (or antiaromatic) radical.

Zwitterionic BODIPYs with large stokes shift: small molecular biomarkers for live cells.

The two first examples of zwitterionic BODIPYs have been synthesized via a simple SN-Ar methodology. The molecules exhibit excellent optical behavior, such as a large Stokes shift in solution and therefore a very intense emission, and can thus avoid self-quenching. The zwitterionic nature of the molecules was unambiguously elucidated using single crystal XRD studies. The electronic conjugation was investigated by NMR, DFT (NICS (0)) and XRD analysis. Due to their inherent ionic nature, their enhanced solubility in aqueous conditions was exploited for their utility in bio-imaging and cell viability studies. These molecules demonstrate promising localization inside live yeast cells.

Novel structurally tuned DAMN receptor for "in situ" diagnosis of bicarbonate in environmental waters.

A new diaminomalenonitrile (DAMN) based charge transfer (CT) chromophore has been designed and synthesized. The receptor demonstrates highly specific and prompt bicarbonate anion (HCO3(-)) sensing in aqueous solution. Interaction with HCO3(-) triggers facile CT across the system, and enables the in situ recognition of water soluble carbonates. The recognition allows us to obtain qualitative as well as quantitative information from aqueous media. The inimitable potential of the receptor was further utilized for monitoring bicarbonate in a range of environmental waters.

Gallium(III)corrole-BODIPY hybrid: novel photophysical properties and first observation of B-F∙∙∙F interactions.

Anchoring a BODIPY onto Ga(III)corrole via a meso-ß linkage facilitated PeT in polar solvents, which quenched the fluorescence, and is further confirmed by electrochemical studies. The triad exhibits unprecedented crystal emission, which is not known for a corrole derivative, due to unique packing. Compound 4 hosts the first example of a novel B-F∙∙∙F interaction as well.

Dual-mode chemodosimetric response of dibromo-BODIPY with anions.

Aromatic nucleophilic substitution (Ar-SN) reaction of 3,5-dibromopentafluorophenyl-BODIPY has been explored as a remarkable basis for selective discrimination of anions. The efficient and characteristic ability of anions to modulate the absorption and emission properties of the dye provides an instantaneous distinction through dual-modes. For the first time, a novel platform to achieve dual-modal and promising recognition with discrimination of a series of anions differing in the nucleophilic atoms (F, O, C and N) has been taken into consideration. The behaviour of various anions with dibromo-BODIPY and vivid signal transduction has been fully established with absorption and emission spectroscopy. In addition to this, recognition events have been unambiguously characterized by (1)H, (19)F-NMR and single-crystal XRD.

First example of a modular porphyrinoid assembly capable of stabilizing different metal ions in a single molecular scaffold.

We report the synthesis and characterization of porphyrin-corrole-porphyrin (Por-Cor-Por) hybrids directly linked at the meso-meso positions for the first time. The stability and solubility of the trimer are carefully balanced by adding electron-withdrawing substituents to the corrole ring and sterically bulky groups on the porphyrins. The new hybrids are capable of stabilizing more than one metal ion in a single molecular scaffold. The versatility of the triad has been demonstrated by successfully stabilizing homo- (Ni) and heterotrinuclear (Ni-Cu-Ni) coordination motifs. The solid-state structure of the NiPor-CuCor-PorNi hybrid was revealed by single-crystal X-ray diffraction studies. The Ni(II) porphyrins are significantly ruffled and tilted by 83° from the plane of corrole. The robustness of the synthesized hybrids was reflected in the electrochemical investigations and the redox behaviour of the hybrids show that the oxidation processes are mostly corrole-centred. In particular it is worth noting that the Por-Cor-Por hybrid can further be manipulated due to the presence of substituent-free meso-positions on both the terminals.

Reusable and specific proton transfer signalling by inorganic cyanide in solution and solid phase.

A highly specific cyanide mediated proton transfer signalling (PTS) is exhibited by a simple diaminomalenonitrile (DAMN) derivative 1. By virtue of the functional groups on it, the chromophore offered a rigid anchoring on a silica surface via a simple dip method, while retaining the recognition behaviour. The PTS triggered a prompt dual-modal display i.e., chromogenic and fluorogenic. The signal readout can be visualized even in micromolar concentrations. It is noteworthy that PTS can be reversed in both solution and solid phases. The remarkable sensitivity of 1 to detect CN(-) from the solution and solid phase envisages a pivotal step towards field-usable sensing.

Corrole-BODIPY Dyads: Synthesis, Structure, and Electrochemical and Photophysical Properties.

A free-base and its Cu(III) derivative of bichromophoric meso-ß linked corrole-BODIPY dyad were synthesized and structurally characterized by single crystal X-ray diffraction (XRD). Both corrole and BODIPY fragments maintained respective ground state electronic isolation despite their connection through a single bond due to a tilted orientation as observed by XRD. This was further supported by UV-vis and cyclic voltammetric studies. The Cu(III)-metalated dyad exhibits temperature-dependent paramagnetic behavior as observed in the variable temperature (1)H NMR due to the presence of a Cu(II)-corrole-π-cation radical. Importantly, the free-base exhibits complete fluorescence quenching probably due to photoinduced electron transfer to a low lying charge separated state. Interestingly, emission was regained upon addition of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) due to the deprotonation of corrole. The "turn on" fluorescence behavior and the presence of acidic NH protons were further exploited toward basic anion sensing utility.

A selective fluoride sensor and a digital processor with "Write-Read-Erase-Read" behaviour.

An easy-to-synthesize Schiff base as a selective and colorimetric fluoride sensor via modulation of intramolecular charge transfer (ICT) has been demonstrated. A typical dual-ion binding property along with its distinct reversibility has been explored for YES, NOR and INH logic functions and a potential "Write-Read-Erase-Read" mimic.