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A series of 1,3,5,7-tetraphenyl-aza-BODIPY dyes functionalized with electron-donating or withdrawing groups at the para-positions of the phenyl rings on either the 1,7- or 3,5-positions were synthesized and characterized. The electron-donating group selected was –NH2, while the electron-withdrawing groups spanned a range of strengths, from strong (-NO2) to moderate (-NH3+) and mild (-Ndouble bondCdouble bondS). The structural modifications were strategically implemented to investigate their impact on the dyes photophysical properties. Spectroscopic studies revealed that these dyes exhibit intense absorption and emission in the near-infrared (NIR) region (678–855 nm). The photophysical properties, including molar absorptivity, fluorescence quantum yield, and Stokes shift were found to depend significantly on both the electronic nature (donating/withdrawing) and positioning (1,7- vs. 3,5-) of the substituents. Complementary computational studies provided insights into the electronic structures and excited-state dynamics, corroborating experimental observations. Time-dependent density functional theory (TD-DFT) calculations revealed that the electron density distribution and the frontier orbitals’ energies and shapes were significantly influenced by the electronic effects of the substituent groups. This study underscores the tunability of aza-BODIPY dyes through rational molecular design, enabling precise control over their optical properties for tailored NIR applications. 

In the title compound, C₈H₈ClNO₂, the acetamide substituent is twisted out of the phenyl plane, forming a dihedral angle of 58.61 (7)°. In the extended structure, each molecule donates two hydrogen bonds [N—H...O(carbonyl) and O—H...O(carbonyl)] and thus also accepts two such hydrogen bonds. The chlorine atom is not involved in the hydrogen bonding. 

In the title compound, C10H12N2O4, the four substituents lie out of the phenyl plane by varying degrees. The methyl C atom lies 0.019 (3) A ˚ out of plane, while the methoxy O and C atoms lie 0.067 (2) and 0.042 (3) A ˚ out of plane, respectively, with the C—C—O—C torsion angle being 3.3 (2). The plane of the nitro group is twisted out of the phenyl plane, forming a dihedral angle of 12.03 (9) with it. The acetamide substituent is twisted considerably more out of the phenyl plane, forming a dihedral angle of 47.24 (6) with it. In the extended structure, the acetamide NH group donates a hydrogen bond to an acetamide carbonyl O atom, thereby forming chains propagating in the [010] direction. 

In the title compound, C16H16N2O3, the phenyl groups are twisted away from coplanarity with the ether linkage, forming a dihedral angle of 59.49 (4) with each other. The ether oxygen atom lies somewhat out of both phenyl planes, by 0.066 (2) and 0.097 (2) A ˚ . The acetamide substituents have quite different conformations with respect to the phenyl groups on either side of the molecule. On one side, the C—C—N—C torsion angle is 21.0 (2), while on the other side it is 76.4 (2). In the crystal, the acetamide N—H groups form intermolecular N—H O hydrogen bonds to acetamide O atom, with both NH groups donating to the same molecule. Thus, ladder-like chains exist in the [101] direction. One of the methyl groups has its H atoms disordered into two orientations, and the crystal chosen for data collection was found to be twinned. 

A method has been developed to prepare previously inaccessible substituted 1,3-benzotellurazoles following an efficient two-step process, consisting of the tellurination of electron rich phenyl ureas with tellurium tetrachloride and subsequent ring closure of the resulting aryl tellurium trichlorides. Tellurination occurs regiospecifically ortho to the urea moiety due to intramolecular Te–O coordination, producing highly crystalline solids that are readily isolated in yields up to 83%. Subsequent ring closure, accomplished by heating with phosphorus trichloride and subsequent reduction with hydrazine hydrate, provides access to 1,3-benzotellurazole derivatives. Selected products were characterized by X-ray crystallography. 

Controlled polymerization for the synthesis of structurally precise conjugated polymers remains a challenging problem in polymer chemistry. Catalyst-transfer polymerization (CTP) based on Pd-catalyzed Suzuki-Miyaura cross-coupling is one of the promising approaches toward solving this challenge. Recent introduction of N-methyliminodiacetic acid (MIDA) boronates as monomers for Suzuki-Miyaura CTP has extended this approach towards a broader variety of monomer structures and led to improved control over the polymerization, particularly for heteroaromatic systems (such as thiophenes). Previously, we found that MIDA-boronate monomers polymerization could be facilitated by Ag+-mediated reaction conditions due to shifting the Pd catalytic cycle toward a more efficient oxo-Pd transmetalation pathway where MIDA-boronates could participate in transmetalation directly, without prior hydrolysis to boronic acid. In this work, we continued studying this novel process, and investigated the dual role of the MIDA-boronate functional group in the case of less reactive fluorenyl (and potentially other all-carbon aromatic systems) monomers. With such monomers, MIDA-boronate group enables the controlled polymerization but also produces a hydrolysis byproduct hindering the polymerization. We also investigated the role of Ag+ acting to counteract this hindering effect. Steric bulkiness of the MIDA-boronate functional group may also slow down the Suzuki-Miyaura CTP process. These complications could reduce the synthetic value of MIDA-boronate monomers in Suzuki-Miyaura CTP, although better understanding of these implications and a proper choice of polymerization conditions and catalytic initiators could to some extent mitigate such problems. As part of this work, we also uncovered a "critical length" phenomenon which results in a dual molecular weight distribution of the resulting conjugated polymer, both with MIDA-boronate and boronic acid monomers. This phenomenon could account for the experimentally observed loss of polymerization control beyond formation of the polymer chains of a certain "critical length", even despite the formally "living" nature of the polymer chains. The generality of this phenomenon and whether it is restricted to using Pd catalytic systems based on Buchwald-type phosphine ligands remains to be studied. Overall, these new findings paint a sophisticated picture of the Suzuki-Miyaura CTP process with MIDA-boronate monomers where the mere presence of a Pd center on the polymer chain is not sufficient to sustain the polymerization (even if a chain could be considered "living" in a sense of possessing a Pd center), and the choice of phosphine ligand on the Pd center is an effective tool to overcome the "critical length" restriction. 

Controlled preparation of structurally precise complex conjugated polymer systems remains to be a major synthetic challenge still to be addressed, and this push is stimulated by the improved device performance as well as unique fundamental characteristics that the well-defined conjugated polymer materials possess. Catalyst-transfer polymerization (CTP) based on Pd-catalyzed Suzuki-Miyaura cross-coupling reaction is currently one of the most promising methods towards achieving such a goal, especially with the recent implementation of N-methyliminodiacetic acid (MIDA) boronates as monomers in CTP. Further expansion and development of practical applications of CTP methods will hinge on a clear mechanistic understanding of both the entire process and the particular steps involved in the catalytic cycle. In this work, we introduced Ag⁺-mediated Suzuki-Miyaura CTP and demonstrated that presence of Ag⁺ shifted a key transmetalation step toward the oxo-Pd pathway, leading to direct participation of MIDA-boronates in the transmetalation step and hence in the polymerization process, and resulting in the overall more efficient polymerization. In addition, we found that, under Ag⁺-mediated conditions, MIDA-boronates can also directly participate in small-molecule cross-coupling reactions. The direct participation of MIDA-boronates in Suzuki-Miyaura cross-coupling has not been envisaged previously and could enable new interesting possibilities to control this reaction both for small-molecule and macromolecular syntheses. In contrast to MIDA-boronates, boronic acid monomers likely undergo transmetalation through an alternative boronate pathway, although they may also be directed to react via the oxo-Pd transmetalation pathway in Ag⁺-mediated conditions. The interplay between the two transmetalation pathways which are both involved in the catalyst-transfer polymerization, and the opportunity to selectively enhance one of them not only improves mechanistic understanding of Suzuki-Miyaura CTP process but also provides a previously unexplored possibility to gain more effective control over the polymerization to obtain structurally better-defined conjugated polymers. 

The introduction of electron-withdrawing groups on 8(meso)-pyridyl-BODIPYs tends to increase the fluorescence quantum yields of this type of compound due to the decrease in electronic charge density on the BODIPY core. A new series of 8(meso)-pyridyl-BODIPYs bearing a 2-, 3-, or 4-pyridyl group was synthesized and functionalized with nitro and chlorine groups at the 2,6-positions. The 2,6-methoxycarbonyl-8-pyridyl-BODIPYs analogs were also synthesized by condensation of 2,4-dimethyl-3-methoxycarbonyl-pyrrole with 2-, 3-, or 4-formylpyridine followed by oxidation and boron complexation. The structures and spectroscopic properties of the new series of 8(meso)-pyridyl-BODIPYs were investigated both experimentally and computationally. The BODIPYs bearing 2,6-methoxycarbonyl groups showed enhanced relative fluorescence quantum yields in polar organic solvents due to their electron-withdrawing effect. However, the introduction of a single nitro group significantly quenched the fluorescence of the BODIPYs and caused hypsochromic shifts in the absorption and emission bands. The introduction of a chloro substituent partially restored the fluorescence of the mono-nitro-BODIPYs and induced significant bathochromic shifts.