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1. 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)

   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 thebis-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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2. Synthesis and photophysical properties of 1,3,5,7-tetraphenyl-aza-BODIPYs substituted at the p-phenyl positions with electron-withdrawing or donating groups

   https://doi.org/10.1016/j.dyepig.2025.113144  

   Dhingra, Simran; Olajuwon, Mistura O; Al_Horani, Masa; Al_Horani, Seleen; Bobadova-Parvanova, Petia; LaMaster, Daniel J; Fronczek, Frank R; Vicente, Maria_da_Graça H (January 2026, Dyes and Pigments)

   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. 

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3. 1,2- cis -Selective glucosylation enabled by halogenated benzyl protecting groups

   https://doi.org/10.1039/d0ob00373e  

   Njeri, Dancan K.; Pertuit, Claude J.; Ragains, Justin R. (April 2020, Organic & Biomolecular Chemistry)

   We report on our initial results from a systematic effort to implement electron-withdrawing protecting groups and Lewis basic solvents/additives as an approach to 1,2- cis (α)-selective O -glucosylation. 1,2- cis -Selective O -glucosylations are reported with thioglucosides and glucosyl trichloroacetimidates and a range of acceptors. A correlation between electron-withdrawing effects and 1,2- cis selectivity has been established. This phenomenon may prove to be broadly applicable in the area of chemical O -glycosylation. 

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4. 8(meso)-Pyridyl-BODIPYs: Effects of 2,6-Substitution with Electron-Withdrawing Nitro, Chloro, and Methoxycarbonyl Groups

   https://doi.org/10.3390/molecules28124581  

   Ndung’U, Caroline; Bobadova-Parvanova, Petia; LaMaster, Daniel J.; Goliber, Dylan; Fronczek, Frank R.; Vicente, Maria da (June 2023, Molecules)

   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. 

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5. Illuminating the Performance of Electron Withdrawing Groups in Halogen Bonding

   https://doi.org/10.1002/cphc.202400607  

   Devore, Daniel_P; Ellington, Thomas_L; Shuford, Kevin_L (November 2024, ChemPhysChem)

   Abstract Throughout the halogen bonding literature, electron withdrawing groups are relied upon heavily for tuning the interaction strength between the halogen bond donor and acceptor; however, the interplay of electronic effects associated with various substituents is less of a focus. This work utilizes computational techniques to study the degree ofσ‐ andπ‐electron donating/accepting character of electron withdrawing groups in a prescribed set of halo‐alkyne, halo‐benzene, and halo‐ethynyl benzene halogen bond donors. We examine how these factors affect theσ‐hole magnitude of the donors as well as the binding strength of the corresponding complexes with an ammonia acceptor. Statistical analyses aid the interpretation of how these substituents influence the properties of the halogen bond donors and complexes, and show that the electron withdrawing groups that are bothσ‐ andπ‐electron accepting form the strongest halogen bond complexes. 

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