Bistable Polyaromatic Aminoboranes: Bright Solid State Emission and Mechanochromism

Reported herein are the synthesis, structure, and intriguing optical characteristics of four new polyaromatic aminoboranes (<b>1</b>–<b>4</b>) bearing dimesitylboron (Mes₂B) as electron-accepting unit(s) and diphenylamine (Ph₂N) as electron-donating unit(s). These compounds are strongly fluorescent in the solid state. Crystalline samples of <b>1</b> and triarylborane-decorated aminoboranes <b>3</b> and <b>4</b> were found to be blue emitters in the solid state. Compounds <b>1</b> and <b>2</b> showed aggregation-induced emission (AIE) and aggregation-induced emission color switching, respectively, while <b>3</b> and <b>4</b> exhibited aggregation-induced emission enhancement. Compounds <b>1</b> and <b>2</b> showed fascinating mechanofluorochromism upon grinding, and such fluorescence changes are due to a crystalline–amorphous phase transition, as confirmed by powder X-ray diffraction studies (PXRD). Interestingly, a ground sample of <b>2</b> was found to be stable and did not revert back upon removal of external stress even after the sample was kept over a long period of time under ambient conditions (more than 6 months). “IPC” was written on a substrate of <b>2</b>, and the part that was touched showed fluorescence different from the rest of the substrate, which could be erased by heating, demonstrating its capability for rewritable data storage devices. The effect of steric and electronic factors on the optical properties of molecules was corroborated by DFT computational studies

Tuning the Phosphorescence and Solid State Luminescence of Triarylborane-Functionalized Acetylacetonato Platinum Complexes

A new series of luminescent cyclometalated platinum complexes with triarylborane-functionalized acetylacetonate ligands is reported. The complexes exhibit solid state luminescence and phosphorescence under ambient conditions. The luminescence color can be tuned from green to red by varying the cyclometalating ligand [2-phenylpyridine (for <b>1</b> and <b>2</b>), 2-thiophenylpyridine (for <b>3</b> and <b>4</b>), 2-thianapthenylpyridine (for <b>5</b> and <b>6</b>)]. The luminescence originates from mixed ³MLCT/³IL [MLCT, metal to ligand charge transfer; IL, intraligand] states of square planar platinum and borane moieties. The π spacer (phenyl or duryl) which connects the boryl and platinum entities has a significant role in determining the photoluminescence efficiency. The bulky duryl spacer in <b>2</b>, <b>4</b>, and <b>6</b> significantly reduces π–π stacking of the square planar platinum moiety in the solid state and provides a rigid backbone, thereby increasing their quantum yield significantly. The role of Lewis-acidic borane on the photoluminescence features is evaluated by fluoride binding experiments

Triarylborane-Appended New Triad and Tetrad: Chromogenic and Fluorogenic Anion Recognition

Facile synthesis of triad <b>3</b> and tetrad <b>4</b> incorporating −B­(Mes)₂ (Mes = mesityl (2,4,6-trimethylphenyl)), boron dipyrromethene (BODIPY), and triphenylamine is reported. Introduction of two dissimilar acceptors (triarylborane and BODIPY) on a single donor resulted in two distinct intramolecular charge transfer processes (amine-to-borane and amine-to-BODIPY). The absorption and emission properties of the new triad and tetrad are highly dependent on individual building units. The nature of electronic communication among the individual fluorophore units has been comprehensively investigated and compared with building units. Compounds <b>3</b> and <b>4</b> showed chromogenic and fluorogenic responses for small anions such as fluoride and cyanide

Revisiting Borylanilines: Unique Solid-State Structures and Insight into Photophysical Properties

The structure and photophysical properties of two known borylanilines, 4-(dimesitylboryl)­aniline (<b>1</b>) and 4-(dimesitylboryl)-3,5-dimethylaniline (<b>2</b>), have been investigated. <b>1</b> and <b>2</b> have similar donor and acceptor centers but differ in their molecular conformations. Compounds <b>1</b> and <b>2</b> have been structurally characterized, and they exhibit a rare form of intermolecular N–H- - -π electrostatic interactions. The structure and photophysical properties of <b>1</b> and <b>2</b> are discussed in the context of computational results

Triarylboron Anchored Luminescent Probes: Selective Detection and Imaging of Thiophenols in the Intracellular Environment

The advances in boron incorporated organics have captured overwhelming interest on account of their outstanding properties and promising applications in various fields. Mostly, triarylborane compounds (TAB) are exploited as sensors of F^– and CN^– anions at the expense of the intrinsic Lewis acidic nature of boron. New molecular probes <b>1</b> and <b>2</b> for detection of toxic thiophenol were designed by conjugating highly fluorescent borylanilines with the luminescent quencher 2,4-dinitrobenzene based sulfonamides (DNBS), wherein the electrophilicity of the DNBS moiety has been modulated by fine-tuning the intrinsic Lewis acidity of boron. The interplay between PET (photoinduced electron transfer) and ICT have been employed for developing the TAB tethered turn-on fluorescent sensor for thiophenol with high selectivity for the first time. The newly developed probes showed very fast response toward thiophenol (within ∼5 min) with limits of detection (LOD) lying in the micromolar range, clearly pointing to their potential. Further, compounds <b>1</b> and <b>2</b> were explored for detecting thiophenol in the intracellular environment by discriminating biothiols. DFT and TD-DFT calculations were performed to support the sensing mechanism

Going beyond Red with a Tri- and Tetracoordinate Boron Conjugate: Intriguing Near-IR Optical Properties and Applications in Anion Sensing

The design and synthesis of a new tri- and tetracoordinate boron conjugate is reported. The conjugate shows broad near-IR emission (∼625–850 nm) and is found to be a selective colorimetric and ratiometric sensor for fluoride ions

Multichannel-Emissive V‑Shaped Boryl-BODIPY Dyads: Synthesis, Structure, and Remarkably Diverse Response toward Fluoride

Three new V-shaped boryl-BODIPY dyads (<b>1–3</b>) were synthesized and structurally characterized. Compounds <b>1–3</b> are structurally close molecular siblings differing only in the number of methyl substituents on the BODIPY moiety that were found to play a major role in determining their photophysical behavior. The dyads show rare forms of multiple-channel emission characteristics arising from different extents of electronic energy transfer (EET) processes between the two covalently linked fluorescent chromophores (borane and BODIPY units). Insights into the origin and nature of their emission behavior were gained from comparison with closely related model molecular systems and related photophysical investigations. Because of the presence of the Lewis acidic triarylborane moiety, the dyads function as highly selective and sensitive fluoride sensors with vastly different response behaviors. When fluoride binds to the tricoordinate borane center, dyad <b>1</b> shows gradual quenching of its BODIPY-dominated emission due to the ceasing of the (borane to BODIPY) EET process. Dyad <b>2</b> shows a ratiometric fluorescence response for fluoride ions. Dyad <b>3</b> forms fluoride-induced nanoaggregates that result in fast and effective quenching of its fluorescence intensity just for ∼0.3 ppm of analyte (i.e., 0.1 equiv ≡ 0.26 ppm of fluoride). The small structural alterations in these three structurally close dyads (<b>1–3</b>) result in exceptionally versatile and unique photophysical behaviors and remarkably diverse responses toward a single analyte, i.e., fluoride ion

Multichannel-Emissive V‑Shaped Boryl-BODIPY Dyads: Synthesis, Structure, and Remarkably Diverse Response toward Fluoride

Three new V-shaped boryl-BODIPY dyads (<b>1–3</b>) were synthesized and structurally characterized. Compounds <b>1–3</b> are structurally close molecular siblings differing only in the number of methyl substituents on the BODIPY moiety that were found to play a major role in determining their photophysical behavior. The dyads show rare forms of multiple-channel emission characteristics arising from different extents of electronic energy transfer (EET) processes between the two covalently linked fluorescent chromophores (borane and BODIPY units). Insights into the origin and nature of their emission behavior were gained from comparison with closely related model molecular systems and related photophysical investigations. Because of the presence of the Lewis acidic triarylborane moiety, the dyads function as highly selective and sensitive fluoride sensors with vastly different response behaviors. When fluoride binds to the tricoordinate borane center, dyad <b>1</b> shows gradual quenching of its BODIPY-dominated emission due to the ceasing of the (borane to BODIPY) EET process. Dyad <b>2</b> shows a ratiometric fluorescence response for fluoride ions. Dyad <b>3</b> forms fluoride-induced nanoaggregates that result in fast and effective quenching of its fluorescence intensity just for ∼0.3 ppm of analyte (i.e., 0.1 equiv ≡ 0.26 ppm of fluoride). The small structural alterations in these three structurally close dyads (<b>1–3</b>) result in exceptionally versatile and unique photophysical behaviors and remarkably diverse responses toward a single analyte, i.e., fluoride ion

Dual Binding Site Assisted Chromogenic and Fluorogenic Recognition and Discrimination of Fluoride and Cyanide by a Peripherally Borylated Metalloporphyrin: Overcoming Anion Interference in Organoboron Based Sensors

Peripherally triarylborane decorated porphyrin (<b>2</b>) and its Zn­(II) complex (<b>3</b>) have been synthesized. Compound <b>3</b> contains of two different Lewis acidic binding sites (Zn­(II) and boron center). Unlike all previously known triarylborane based sensors, the optical responses of <b>3</b> toward fluoride and cyanide are distinctively different, thus enabling the discrimination of these two interfering anions. Metalloporphyrin <b>3</b> shows a multiple channel fluorogenic response toward fluoride and cyanide and also a selective visual colorimetric response toward cyanide. By comparison with model systems and from detailed photophysical studies on <b>2</b> and <b>3</b>, we conclude that the preferential binding of fluoride occurs at the peripheral borane moieties resulting in the cessation of the EET (electronic energy transfer) process from borane to porphyrin core and with negligible negetive cooperative effects. On the other hand, cyanide binding occurs at the Zn­(II) core leading to drastic changes in its absorption behavior which can be followed by the naked eye. Such changes are not observed when the boryl substituent is absent (e.g., Zn-TPP and TPP). Compounds <b>2</b> and <b>3</b> were also found to be capable of extracting fluoride from aqueous medium

Tetraphenylethene–2-Pyrone Conjugate: Aggregation-Induced Emission Study and Explosives Sensor

Design and synthesis of a novel tetraphenylethene–2-pyrone <b>(TPEP)</b> conjugate exhibiting donor–acceptor characteristics is reported. The localized frontier molecular orbitals (DFT studies) and the solvent polarity dependent photoluminescence characteristics directly corroborate the presence of intramolecular charge transfer character in <b>TPEP</b>. <b>TPEP</b> is poorly emissive in the solution state. In contrast, upon aggregation (THF/water mixtures), <b>TPEP</b> exhibits aggregation-induced emission enhancement. Upon aggregation, dyad <b>TPEP</b> forms a fluorescent nanoaggregate which was confirmed by transmission electron microscopy imaging studies. The luminescence nanoaggregates were elegantly exploited for selective detection of nitro aromatic compounds (NACs). It was found that nanoaggregates of <b>TPEP</b> were selectively sensing the picric acid over the other NACs. Efficiency of the quenching process was further evaluated by the Stern–Volmer equation. <b>TPEP</b>-based low-cost fluorescent test strips were developed for the selective detection of picric acid