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We present a new class of blue circularly polarized luminescent emitters based on tetraarylaminoborane (TAAB) with considerable dissymmetry factor in the solid state. The chiral pendant 1-phenylethylamine in BN- RR and BN- SS imparts chirality to the core chromophore, resulting in circularly polarized luminescence signals ( g lum = 0.8 × 10 -3 ) with a quantum yield of 33% in the crystalline state. This novel set of compounds also showcases intriguing thermally reversible piezochromism.

Herein, we report the synthesis, molecular structure, and optical features of tetrarylaminoboranes 1 (Mes 2 B-N(Ph)(C 10 H 7 )) and 2 (Mes 2 B-N(Ph)(C 14 H 9 )). In the solution state, 1 shows aggregation-induced emission enhancement and color switching, while 2 displays emission color switching and aggregation-caused quenching. At 77 K, frozen solutions of 1 show delayed fluorescence (DF) and phosphorescence, whereas 2 display only DF. Pristine solids of 1 and 2 showed delayed fluorescence under ambient conditions; however, crystals of both compounds show no phosphorescence under similar conditions. Polymethyl methacrylate thin films of 1 (1 wt % doping concentration) exhibit persistent room-temperature phosphorescence (pRTP) lasting for ∼0.5 s. In contrast, 2 does not show phosphorescence under similar conditions. Systematic photophysical studies and theoretical (DFT and TD-DFT) calculations are performed on these molecules to rationalize their intriguing optical characteristics.

Herein, we report the design and synthesis of far-red emissive boryl-thiophene-BODIPY triads 1-3 . The π-conjugation length and electronic communication between borane and BODIPY moieties are tuned by judiciously varying the size of the oligothiophene spacer in these triads ( 1 , terthiophene; 2 , quarterthiophene; and 3 , pentathiophene). Conjugates 1-3 showed intriguing triple emissions in the blue to far-red regions. Detailed optical, time-resolved decay kinetics, time-resolved area-normalized emission spectra (TRANES), fluoride binding, and computational studies suggest that the multiple emissions in these triads are due to an inefficient transfer of energy from the boryl-oligothiophene to the BODIPY unit. In addition, all of the conjugates showed a ratiometric fluorescence response to fluoride ions.

We studied the dual emission characteristics of a series of boryl-BODIPYs ( 1 - 6 ) comprised of triarylborane (TAB) as an energy donor and BODIPY as an energy acceptor. The molecular conformations of dyads 1 - 6 were systematically tuned by judiciously changing the spacer that bridged the boryl and BODIPY moieties. Frontier molecular orbitals (FMOs) are localized in 3 , 4 , and 6 with a twisted molecular conformation. In contrast, FMOs are significantly delocalized in 1 , 2 , and 5 with the least-twisted molecular conformation. Dyads 1 - 6 showed dual emission features when they were excited at the TAB-dominated absorption band. However, the ratio between the two emission bands in 1 - 6 significantly varied depending on the molecular conformations. Systematic photoluminescence (PL) studies (both steady-state and time-resolved PL) together with computational, crystal structure, and anion binding studies established that the frustrated excited-state energy transfer from borane to BODIPY is the cause of the dual emission features in these molecular dyads. These studies also revealed that the energy transfer from borane to BODIPY can be elegantly tuned by modulating the dihedral angle between these two moieties.

Three new triads [bis(mesityl)boryl (Mes 2 B)-vinylbithiophene-BODIPY] bearing zero ( 1 ), two ( 2 ), and four ( 3 ) methyl groups on the BODIPY core are synthesized, and their optical properties are reported. The vinyl linker between the thiophene rings in the spacer moiety improved the electronic communication between the boryl and BODIPY units. It displayed a bathochromic shift in the absorption and emission spectra compared to the Mes 2 B-bithiophene-BODIPY triad reported elsewhere. These compounds exhibit intriguing multiple-emission features due to an incomplete energy transfer from donor borane to the acceptor BODIPY unit. These compounds' photoluminescence color can be conveniently fine-tuned by fluoride binding at the coordinatively unsaturated tricoordinate boron center. Triad 3 , with a rigid molecular structure, showed a sharp emission band, whereas triads 1 and 2 , with flexible molecular structures, displayed broad emission bands with a robust bathochromic shift, ascribed to their excited state structural reorganizations. These triads selectively bind fluoride ions and show colorimetric responses, which can be seen with an unaided eye. DFT computational studies were performed to rationalize the optical signatures of these compounds.

We study the effect of molecular conformation on the electronic coupling between the donor amines and acceptor 1,8-naphthalimide (NPI) in a series of D-A systems 1 - 4 (A = NPI; D = phenothiazine, phenoxazine, carbazole, diphenylamine, respectively, for 1 , 2 , 3 , and 4 ). Weakly coupled systems show dual emission in the solution state, while strongly coupled systems show single emission bands. The energy of transitions and photoluminescence (PL) quantum yield are sensitive to the molecular conformation and donor strength. These compounds show delayed emission in the solutions and aggregated state and phosphorescence in the solid state. Compounds 3 and 4 with weak donors exhibit intermolecular slipped π···π interactions in the solid state and consequently exhibit dual (intra- and inter-) phosphorescence at low temperature. Steady state and time-resolved PL studies at variable temperature together with computational and crystal structure analysis were used to rationalize the optical properties of these compounds. The delayed emission of these compounds is sensitive to molecular oxygen; accordingly, these molecules are utilized for differential imaging of normoxia and hypoxia cancer cells.

A donor-π-acceptor strategy is being well exploited in several fields in view of their robust optical properties. However, the impact of branching in quadrupolar [A-(π-D) 2 ] and octupolar [A-(π-D) 3 ] molecules in comparison to parent dipolar (A-π-D) molecules on the delayed fluorescence and phosphorescence properties is seldom explored. We have presented herein the distinct and contrasting optical properties of a tridurylborane core bearing -NH 2 ( 1 - 3 ) and -NMe 2 ( 4 - 6 ) donor moieties, wherein the number of donors is increased systematically. Because of propeller molecular architecture, the donor and acceptor are weakly coupled, and the frontier molecular orbitals are spatially localized. All of the compounds show delayed fluorescence under ambient conditions and persistent phosphorescence at low temperature. Solvent-dependent studies and temperature-dependent luminescence measurements established that quadrupolar ( 2 and 5 ) and octupolar ( 3 and 6 ) compounds underwent symmetry breaking in the excited state. Curiously, delayed fluorescence and phosphorescence spectra are found to be blue-shifted and follow the same trend as the fluorescence upon an increase in the branches. The highest quantum yield was observed for dipolar compounds. Besides, the phosphorescence lifetime decreases with an increase in the number of branches. These interesting experimental observations are further supported by quantum-mechanical calculations.

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 1 and 2 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 1 and 2 were explored for detecting thiophenol in the intracellular environment by discriminating biothiols. DFT and TD-DFT calculations were performed to support the sensing mechanism.

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 1 and 2), 2-thiophenylpyridine (for 3 and 4), 2-thianapthenylpyridine (for 5 and 6)]. The luminescence originates from mixed 3 MLCT/ 3 IL [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 2, 4, and 6 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.

Design and synthesis of a novel tetraphenylethene-2-pyrone (TPEP) 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 TPEP. TPEP is poorly emissive in the solution state. In contrast, upon aggregation (THF/water mixtures), TPEP exhibits aggregation-induced emission enhancement. Upon aggregation, dyad TPEP 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 TPEP were selectively sensing the picric acid over the other NACs. Efficiency of the quenching process was further evaluated by the Stern-Volmer equation. TPEP-based low-cost fluorescent test strips were developed for the selective detection of picric acid.

Pyrene containing Schiff base molecule, namely 4-[(pyren-1-ylmethylene)amino]phenol (KB-1), was successfully synthesized and well characterized by using (1)H, (13)C NMR, FT-IR, and EI-MS spectrometry. UV-visible absorption, steady-state fluorescence, time-resolved fluorescence, and transient absorption spectroscopic techniques have been employed to elucidate the photophysical processes of KB-1. It has been demonstrated that the absorption characteristics of KB-1 have been bathochromatically tuned to the visible region by extending the π-conjugation. The extended π-conjugation is evidently confirmed by DFT calculations and reveals that π→π* transition is the major factor responsible for electronic absorption of KB-1. The photophysical property of KB-1 was carefully examined in different organic solvents at different concentrations and the results show that the fluorescence of this molecule is completely quenched due to photoinduced electron transfer. Intriguingly, the fluorescence intensity of KB-1 increases enormously by the gradual addition of water up to 90% with concomitant increase in fluorescence lifetime. This clearly signifies that this molecule has aggregation-induced emission (AIE) property. The mechanism of AIE of this molecule is suppression of photoinduced electron transfer (PET) due to hydrogen bonding interaction of imine donor with water. A direct evidence of PET process has been presented by using nanosecond transient absorption measurements. Further, KB-1 was successfully used for antimicrobial and bioimaging studies. The antimicrobial studies were carried out through disc diffusion method. KB-1 is used against both Gram-positive (Rhodococcus rhodochrous and Staphylococcus aureus) and Gram-negative (Escherichia coli and Pseudomonas aeruginosa) bacterial species and also fungal species (Candida albicans). The result shows KB-1 can act as an excellent antimicrobial agent and as a photolabeling agent. S. aureus, P. aeruginosa, and C. albicans were found to be the most susceptible microorganisms at 1 mM concentration among the bacteria used in the present investigation.

Three new V-shaped boryl-BODIPY dyads (1-3) were synthesized and structurally characterized. Compounds 1-3 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 1 shows gradual quenching of its BODIPY-dominated emission due to the ceasing of the (borane to BODIPY) EET process. Dyad 2 shows a ratiometric fluorescence response for fluoride ions. Dyad 3 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 (1-3) result in exceptionally versatile and unique photophysical behaviors and remarkably diverse responses toward a single analyte, i.e., fluoride ion.

Peripherally triarylborane decorated porphyrin (2) and its Zn(II) complex (3) have been synthesized. Compound 3 contains of two different Lewis acidic binding sites (Zn(II) and boron center). Unlike all previously known triarylborane based sensors, the optical responses of 3 toward fluoride and cyanide are distinctively different, thus enabling the discrimination of these two interfering anions. Metalloporphyrin 3 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 2 and 3, 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 2 and 3 were also found to be capable of extracting fluoride from aqueous medium.

Facile synthesis of triad 3 and tetrad 4 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 3 and 4 showed chromogenic and fluorogenic responses for small anions such as fluoride and cyanide.

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.

Organooxotin cages, clusters, and coordination polymers containing [Sn 2(mu-O)], [Sn 2(mu-OH)], [Sn 2(mu-O) 2], [Sn 2(mu-OH) 2], and [Sn 3(mu 3-O)(mu-OR) 3] building blocks have been assembled by the reactions of organotin precursors with phosphonic, phosphinic, carboxylic, or sulfonic acids. Various synthetic methodologies including Sn-C bond cleavage reactions and solventless procedures have been utilized to generate several nanodimensional organostannoxane assemblies. The synthesis, structure, and structural interrelationship of these diverse organostannoxane compounds are discussed. The synthetic knowledge gained to prepare specific organostannoxane structural forms in high yields has been utilized for the construction of dendrimer-like molecules. These contain a central stannoxane core and a functional periphery. The functional periphery can be readily modulated to assemble photoactive, electroactive, or multisite coordinating molecules. The synthesis, structure, and potential uses of these compounds are discussed.

A hydroxyl-rich hexameric organooxotin prismane has been prepared by reaction of n-BuSn(O)OH with 9-hydroxy-9-fluorenecarboxylic acid. The supramolecular structure of this cage shows channels with hydrophobic and hydrophilic segments, which selectively entrap guest molecules.