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1. Intramolecular Stabilization of Naphtho[2,1- b :3,4- b ′]dithiophenes: Synthesis and Analysis of Imine-Based Chromophores

   https://doi.org/10.1021/acs.joc.5c02486  

   Adusei, Emmanuel_B A; Ibrahim, Sarah; Jenneker, Kara; Goldsmith, Calvin D; Dragoi, Danielle; Zeller, Matthias; Kinney, Zacharias J (December 2025, The Journal of Organic Chemistry)

   The role of noncovalent interactions in stabilizing and organizing complex structures throughout nature is indisputable. Of the various classes of noncovalent interactions, those that involve secondary bonding – attractive interactions between σ-hole and nucleophile – are of interest in the design of materials due to their strength and programmability. This report takes the approach of placing nucleophilic imines in close proximity to fused thiophene moieties within naphtho[2,1-b:3,4-b′]dithiophene (α NDT) cores, where an intramolecular N···S interaction is poised to yield rigid chromophores. These types of intramolecular N···S interactions have been observed in the solid-state for several decades, but their solution-state analysis remains rare. Here we detail how crystallography, 1H/13C NMR spectroscopy, and molecular modeling work synergistically to describe the strength and impact of intramolecular N···S interactions on α NDT chromophores α(1)2. The remote substituents on the aryl amines (1) employed as condensation partners have minimal structural impact on the α(1)2 series, but the photophysical properties of strongly electron-deficient (1d and 1dd) or polarizing (1c and 1cc) end-caps are enhanced in comparison to their neutral (1a) and weak (1b and 1bb) counterparts. This design strategy to incorporate intramolecular N···S interactions highlights how NDTs can be incorporated into complex architectures in a programmable manner. 

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2. Designing Thiadiazoloquinoxaline-Based Conjugated Polymers for Efficient Organic Photovoltaics: A DFT/TDDFT Study

   https://doi.org/10.3390/molecules29071580  

   Dorlus, Taylor A; Roy, Juganta K; Leszczynski, Jerzy (April 2024, Molecules)

   Clean and renewable energy development is becoming frontier research for future energy resources, as renewable energy offers sustainable and environmentally friendly alternatives to non-renewable sources such as fossil fuels. Among various renewable energy sources, tremendous progress has been made in converting solar energy to electric energy by developing efficient organic photovoltaics. Organic photovoltaic materials comprising conjugated polymers (CP) with narrow optical energy gaps are promising candidates for developing sustainable sources due to their potentially lower manufacturing costs. Organic semiconductor materials with a high electron affinity are required for many optoelectronic applications. We have designed a series of organic semiconductors comprised of cyclopentadithiophene as a donor and thiadiazoloquinoxaline (TQ) as an acceptor, varying the π-conjugation and TQ-derivatives. We have employed density functional theory (DFT) and time-dependent DFT (TDDFT) to evaluate the designed CP’s optoelectronic properties, such as optical energy gap, dipole moment, and absorption spectra. Our DFT/TDDFT result shows that the energy gap of CPs is lowered and redshifted in the absorption spectra if there is no insertion of conjugation units such as thiophene and selenophene between donor and acceptor. In addition, selenophene shows relatively better redshift behavior compared to thiophene. Our work also provides rational insight into designing donor/acceptor-based CPs for organic solar cells. 

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3. Luminescent 1 H -1,3-benzazaphospholes

   https://doi.org/10.1039/d2ra07226b  

   Evariste, Sloane; Harrison, Alexandra M.; Sarkar, Sunandan; Rheingold, Arnold L.; Dunietz, Barry D.; Heinicke, Joachim W.; Delgado Rosario, Emalyn; Yoon, Sungwoon; Teets, Thomas S.; Protasiewicz, John D. (December 2022, RSC Advances)

   2-R-1 H -1,3-Benzazaphospholes (R-BAPs) are an interesting class of σ 2 P heterocycles containing PC bonds. While closely related 2-R-1,3-benzoxaphospholes (R-BOPs) have been shown to be highly photoluminescent materials depending on specific R substituents, photoluminescence of R-BAPs has been previously limited to an example having a fused carbazole ring system. Here we detail the synthesis and structural characterization of a new R-BAP (3c, R = 2,2′-dithiophene), and compare its photoluminescence against two previously reported R-BAPs (3a, R, R′ = Me and 3b, R = 2-thiophene). The significant fluorescence displayed by the thiophene derivatives 3b ( φ = 0.53) and 3c ( φ = 0.12) stands in contrast to the weakly emissive methyl substituted analogue 3a ( φ = 0.08). Comparative computational investigations of 3a–c offer insights into the interplay between structure–function relationships affecting excited state relaxation processes. 

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4. Regioselective Synthesis of Ambipolar B–N Lewis Pair Functionalized Pyrenes: Structural Dynamics, Emission Tuning, and Applications in Live Cell Imaging and as Electrochemiluminescent Materials

   https://doi.org/10.1021/jacs.5c22679  

   Vanga, Mukundam; Jahanghiri, Sara; Davis, Justin; Nandi, Rajendra Prasad; Sahoo, Ashutosh; Kucheryavy, Pavel; Lalancette, Roger A; Bonder, Edward M; Ding, Zhifeng; Jäkle, Frieder (March 2026, Journal of the American Chemical Society)

   Intramolecular B←N Lewis pair functionalization of polycyclic aromatic hydrocarbons (PAHs) is emerging as a powerful strategy for tailoring their optical and electronic properties to specific applications. Herein, we report the design and synthesis of four quadrupolar pyrene fluorophores containing triarylamine donor and pyridyl-borane acceptor substituents by N-directed electrophilic C-H borylation in the K-region. Introduction of rigid six-membered B-N heterocycles greatly decreased the lowest unoccupied molecular orbital (LUMO) energy levels and redshifted the absorption and emission maxima compared to the non-borylated precursors. These pyrenes exhibit absorptions spanning the entire visible region and intense deep red to near-infrared fluorescence, with impressive quantum yields as high as 82%. The simultaneous presence of pyridyl-borane acceptor and arylamine donor units also enables facile reversible multi-redox oxidation and reduction processes. The advantageous photophysical and electrochemical characteristics are highly attractive for optoelectronic devices and (bio)imaging applications. The pyrene derivative with the most redshifted emission, 5-Pf, was further evaluated in live cell imaging studies, showing effective staining of acidic compartments, including lysosomes. In addition, we demonstrate the outstanding performance of 5-Pf as a novel electrochemiluminescent (ECL) luminophore through annihilation and coreactant experiments in cyclic voltammetry and pulsing modes. Spooling ECL spectroscopy revealed a strong emission with a maximum at 646 nm, in good agreement with the photo-induced emission maximum at 660 nm. A superior absolute ECL efficiency (ФECL) of up to 0.9 ± 0.1 %, exceeding that of typically employed [Ru(bpy)3]2+, was achieved during CV scanning with benzoyl peroxide as a coreactant. 

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5. Deciphering the unusual fluorescence in weakly coupled bis-nitro-pyrrolo[3,2-b]pyrroles

   https://doi.org/10.1038/s42004-020-00434-6  

   Poronik, Yevgen M.; Baryshnikov, Glib V.; Deperasińska, Irena; Espinoza, Eli M.; Clark, John A.; Ågren, Hans; Gryko, Daniel T.; Vullev, Valentine I. (December 2020, Communications Chemistry)

   null (Ed.)

   Abstract Electron-deficient π-conjugated functional dyes lie at the heart of organic optoelectronics. Adding nitro groups to aromatic compounds usually quenches their fluorescence via inter-system crossing (ISC) or internal conversion (IC). While strong electronic coupling of the nitro groups with the dyes ensures the benefits from these electron-withdrawing substituents, it also leads to fluorescence quenching. Here, we demonstrate how such electronic coupling affects the photophysics of acceptor–donor–acceptor fluorescent dyes, with nitrophenyl acceptors and a pyrrolo[3,2- b ]pyrrole donor. The position of the nitro groups and the donor-acceptor distance strongly affect the fluorescence properties of the bis -nitrotetraphenylpyrrolopyrroles. Concurrently, increasing solvent polarity quenches the emission that recovers upon solidifying the media. Intramolecular charge transfer (CT) and molecular dynamics, therefore, govern the fluorescence of these nitro-aromatics. While balanced donor-acceptor coupling ensures fast radiative deactivation and slow ISC essential for large fluorescence quantum yields, vibronic borrowing accounts for medium dependent IC via back CT. These mechanistic paradigms set important design principles for molecular photonics and electronics. 

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