Pentagon-embedded N-doped coumarinacenes: tandem synthesis and tunable photophysical attributes for biomolecular probing.

We have synthesized a novel series of nitrogen-doped pentagon-embedded coumarinacenes, namely carbazole-coumarins, a tandem 1,4-elimination Diels-Alder aromatization reaction. These planar, -substituted carbazole-coumarins exhibit excellent functionalizability, enhanced photostability and solvent polarity-tunable absorption and blue-to-red emission with notably high fluorescence quantum yields, attesting to their remarkable photophysical properties. These attributes highlight the carbazole-coumarins' potential as robust and efficient fluorescent materials for diverse applications in various fields, including as probes for studying biomolecular systems and dynamics.

From Serendipity to Precision: Decoding the Enigma of Rearrangement in Scholl-Type Reactions for Programmable Cyclization.

Rearrangements in the Scholl reaction have traditionally been serendipitous, lacking a systematic approach for synthesizing rearranged and cyclized products. This paper introduces a strategic pathway to achieve rearranged-cyclized thienotetrahelicene derivatives over direct-cyclized chrysenothiophene derivatives by finely modifying the reaction conditions and tuning the electronic properties in Scholl-type reaction precursors, tetraarylthiophenes. Through careful design principles, we demonstrate the programmable synthesis of these distinct products.

Effects of donor and acceptor substituents on the photophysics of 4-ethynyl-2,1,3-benzothiadiazole derivatives.

The present work explores the photophysical, electrochemical, and fluorescence polarization properties of a group of π-conjugated phenylethynyl-2,1,3-benzothiadiazole derivatives (BTDs) bearing different electron-donating (ED) or electron-withdrawing (EW) substituents at the position of the phenylethynyl moiety. The BTDs were synthesized through the Sonogashira cross-coupling reaction between 4-bromo-2,1,3-benzothiadiazole and the respective -substituted phenylethynyl derivatives. The BTDs with the EW-substituents show relatively weak solvatochromic behavior, while the BTDs with the strong ED-substituents like methoxy and ,-dimethylamino-based substituents (BTDPhOMe and BTDPhNMe2) exhibit a pronounced solvatochromic behavior.

Chasing Turns and Twists: Unraveling the One-Step Synthesis, Intricate Pathways, and Structural Revelations of N-Aryl Aza-quasi[8]circulenes.

An efficient one-step synthesis of N-Aryl aza-quasi[8]circulenes is reported starting from bis(biaryl)carbazoles. The intermediacy of N-aryl aza[7]helicene is investigated, and the Scholl oxidative cyclization route is invoked here to overcome the large strain during the formation of N-aryl aza-quasi[8]circulenes from N-aryl aza[7]helicene. Notably, this transformation occurs without the need for directing groups and proceeds from a more helical to a less helical pathway.

Leveraging Torsional and Steric Strains: A Pre-macrocyclization Strategy Enables Conformation-Specific Fullerene Binding in m-Cyclophanes.

Though the chemistry of resorcinarenes is half a century old, the conformationally-locked resorcinarene crowns are generally constructed using hydrogen bonds or covalent tethers. Often, covalent tethering involves extra post-macrocyclization steps involving upper-rim functionalities. We have leveraged the torsional and steric strains through α-substituents of the lower-rim C-alkyl chains and accomplished conformationally-rigid fluorescent m-cyclophane deep-crowns in a predetermined way.

Phenylethynylanthracene based push-pull molecular systems: tuning the photophysics through -substituents on the phenyl ring.

Organic push-pull molecules contain donor and acceptor moieties connected π-linkages through which intramolecular electron charge transfer (ICT) can occur in the ground and excited states; giving these molecules interesting photophysical properties. The molecules chosen in this work are some basic phenylethynylanthracene derivatives to show that with just a change of substituents this class of small molecules can show dramatic changes in their photophysical properties. The emission properties and ICT abilities of these molecules are compared with regards to various electron donating and withdrawing substituents.

Rearrangements in Scholl Reaction.

Rearrangements in Scholl reaction are mostly serendipitous. The design of molecular precursors is what seems to guide the course of rearrangement. This review consolidates different classes of precursors used in Scholl reaction and their accompanying rearrangements that include aryl migration, migration followed by cyclization and skeletal rearrangements involving ring expansion, ring contraction and both, under the reaction conditions.

Coronene-embedded 'super' coumarins.

A non-planar π-enlarged coronene-embedded coumarin achieved pyranone annulation and its cyanated derivative possess bright orange to red emission in both solution and solid states, with scope for bioimaging applications. The multiple redox states, frontier molecular orbital energy levels and strong cofacial π-stacking ability point towards applications in organic optoelectronics.

Steering Scholl Oxidative Heterocoupling by Tuning Topology and Electronics for Building Thiananographenes and Their Functional N-/C-Congeners.

While intramolecular Scholl oxidative coupling between two arenes is common, successful C-C heterocoupling between thiophene and arene is scarce. The latter is due to the notorious reactivity of thiophene towards polymerization under oxidative conditions. This report systematically demonstrates how topological variation of electronics and reactivity in thiophene substrates can lead to efficient oxidative heterocoupling.

Accessing []-Face π-Expanded Fluorescent Coumarins by Scholl Cyclization.

[]-Face π-expanded coumarins are synthesized by employing the Scholl cyclization method. These new arene-annulated dipolar coumarins display interesting absorption and fluorescent properties. The large Stokes shifts, tuneable fluorescent quantum yields, and high photostability reveal promise in bioimaging application.

Oxidative Coupling of Carbazoles: A Substituent-Governed Regioselectivity Profile.

Oxidative C-C coupling of carbazoles possessing various substituents is demonstrated in the presence of organic (metal-free) recyclable oxidants, such as DDQ or CA/H, for accessing bicarbazole regioisomers. Differently substituted carbazoles are examined to showcase regioselective discrimination (3,3'- versus 1,3'-bicarbazoles) and preferences based on sterics and electronics in oxidative coupling. Finally, a mechanism that involves the carbazole radical cation has been traced (evidenced) and proposed on the basis of the UV-vis-NIR absorption and EPR spectroscopy results.

Coumarin[4]arene: A Fluorescent Macrocycle.

The pyranone functionalization of the upper rim of resorcinarene to provide the coumarin macrocycle called "coumarin[4]arene", possessing visible fluorescence and conformationally flexible behavior suitable for molecular recognition, has been successfully synthesized and characterized.

Linear and Nonlinear Optical Properties of Tricyanopropylidene-Based Merocyanine Dyes: Synergistic Experimental and Theoretical Investigations.

New merocyanines dyes with tricyanopropylidene-based acceptor units connected to dihexylaminophenyl or dihexylaminothiophenyl donor moieties through polyenic bridges of different lengths have been designed. All derivatives exhibited a strong dipolar character and showed a typical intramolecular charge transfer (ICT) transition. NMR spectroscopy experiments combined with DFT calculations demonstrated that both the nature of the donor-acceptor pair and the length of the conjugated linker strongly impact the electronic structure of the dyes and induce alteration in the bond-length alternation (BLA) and marked shifts in the ICT absorption bands.

Metal-Free Oxidative C-C Coupling of Arylamines Using a Quinone-Based Organic Oxidant.

A variety of arylamines are shown to undergo oxidative C-C bond formation using quinone-based chloranil/H reagent as the recyclable organic (metal-free) oxidant system to afford benzidines/naphthidines. Arylamines (3°/2°) designed with various substituents were employed to understand the steric as well as electronic preferences of oxidative dimerization, and a mechanism involving amine radical cation has been proposed. The tetraphenylbenzidine derivative obtained via oxidative C-C coupling has been further converted to blue-emissive hole-transporting material via a simple chemical transformation.

Bigger and Brighter Fluorenes: Facile π-Expansion, Brilliant Emission and Sensing of Nitroaromatics.

π-Expanded butterfly-like 2D fluorenes and 3D spirobifluorenes 1-5 were synthesized via a DDQ-mediated oxidative cyclization strategy with a high regioselectivity. Through structural modification via π-expansion, it was possible to achieve near-ultraviolet absorption, bright-blue emission, very high near-unity fluorescence quantum yields in solution as well as in film states, and deep-lying HOMO energy levels with excellent thermal stabilities. Furthermore, these electron-rich compounds displayed a notable behavior towards sensing of nitroaromatic explosives, such as picric acid, up to a detection limit of 0.

Combination of Cyanine Behaviour and Giant Hyperpolarisability in Novel Merocyanine Dyes: Beyond the Bond Length Alternation (BLA) Paradigm.

Merocyanine dyes that exhibit antithetic cyanine-like behaviour and giant first-order hyperpolarisability (β) values have been designed. These cyanine-type dyes open up an intriguing route towards molecular-based electro-optic materials as well as new second-harmonic generation dyes for imaging.

Combined transparency and optical nonlinearity enhancement in flexible covalent multimers by operating through-space interactions between dipolar chromophores.

Subtle manipulation of mutual repulsion and polarisation effects between polar and polarisable chromophores forced in closed proximity allows achieving major (100%) enhancement of the first hyperpolarisability together with increased transparency, breaking the well-known nonlinearity-transparency trade-off paradigm.

Dipolar versus octupolar triphenylamine-based fluorescent organic nanoparticles as brilliant one- and two-photon emitters for (bio)imaging.

Two related triphenylamine-based dipolar and octupolar fluorophores are used to prepare aqueous suspensions of fluorescent organic nanoparticles (FONs) via the reprecipitation method. The obtained spherical nanoparticles (30-40 nm in diameter) are fluorescent in aqueous solution (up to 15% fluorescence quantum yield) and exhibit extremely high one- and two-photon brightness, superior to those obtained for quantum dots. Despite the two chromophores showing similar fluorescence in solution, the fluorescence of FONs made from the octupolar derivative is significantly red-shifted compared to that generated by the dipolar FONs.

The effectiveness of essential-state models in the description of optical properties of branched push-pull chromophores.

In this paper we present the synthesis, spectroscopic characterization and theoretical modelling of two pairs of correlated dipolar and octupolar donor-acceptor conjugated chromophores, based on the triphenylamine branching centre. The two pairs of chromophores differ for the electron withdrawing end-groups. Linear absorption, fluorescence and two-photon absorption of all the compounds in different solvents can be well described by the use of charge-resonance theoretical models based on essential-state descriptions of the electronic structure, and taking into account the coupling to effective molecular vibrations and to polar solvation degrees of freedom.

Nondoped pure-blue OLEDs based on amorphous phenylenevinylene-functionalized twisted bimesitylenes.

The twisted bimesitylene scaffold hinders crystallization and imparts amorphous nature to the oligophenylenevinylenes (OPVs) generated by 2- and/or 4-fold functionalization. The resultant phenylenevinylenes 1-5 with unique molecular topology exhibit excellent thermal and solid-state luminescence properties. The amorphous nature permits their application as pure-blue emissive materials in OLEDs.

De novo design for functional amorphous materials: synthesis and thermal and light-emitting properties of twisted anthracene-functionalized bimesitylenes.

The unique structural attributes inherent to D(2d)-symmetric rigid tetraarylbimesityls render their close packing in the solid state difficult. We have exploited the indisposed tendency of such modules based on the bimesityl scaffold toward crystallization to design a novel class of amorphous functional materials with high glass transition temperatures and thermal stability (T(d) > 400 degrees C). It is shown that a variety of 2- and 4-fold anthracene-functionalized bimesityls, 1-7, that exhibit excellent amorphous properties (T(g) = ca.

Blue light-emitting and hole-transporting amorphous molecular materials based on diarylaminobiphenyl-functionalized bimesitylenes.

The diarylaminobiphenyl-functionalized bimesityls and exhibit amorphous nature, high thermal stability and excellent blue emission in the solid state. They serve as both hole-transporting and emissive materials in OLEDs for blue emission with high external quantum efficiencies.

Steric inhibition of pi-stacking: 1,3,6,8-tetraarylpyrenes as efficient blue emitters in organic light emitting diodes (OLEDs).

The sterically congested tetraarylpyrenes 1-3, which can be readily accessed by Suzuki coupling, exhibit no-aggregation (pi-stacking) behavior in both solution and solid states. The indisposed tendency of 1-3 toward crystallization and their moderate molecular dimensions permit exploitation as blue light emitting materials in OLEDs with respectable device performances.

Novel photochromism of differently-linked bis-benzopyrans.

The unique photochromic bis-chromene 5 incorporates the structural attributes of both 3 and 4 . UV-vis irradiation of 5 leads to a dark brown colour, which is formed by mixing the purple and red colours observed for the photolysates of 3 and 4 , respectively.