Synthesis and characterization of novel BODIPYs and their antioxidant, antimicrobial, photodynamic antimicrobial, antibiofilm and DNA interaction activities

In the current study, we synthesized and characterized new BODIPY derivatives (1-4) having pyridine or thienyl-pyridine substituents at meso- position and 4-dibenzothienyl or benzo[b]thien-2-yl moieties at 2-,6- positions. We investigated fluorescence properties and the ability to form singlet oxygen. In addition, various biological activities of BODIPYs such as DPPH scavenging, DNA binding/cleavage ability, cell viability inhibition, antimicrobial activity, antimicrobial photodynamic therapy (aPDT) and biofilm inhibition properties were performed. BODIPY derivatives BDPY-3 (3) and BDPY-4 (4) have high fluorescence quantum yields as 0.50 and 0.61 and 1 O2 quantum yields were calculated as 0.83 for BDPY-1 (1), 0.12 for BDPY-2 (2), 0.11 for BDPY-3 and 0.23 for BDPY-4. BODIPY derivatives BDPY-2, BDPY-3 and BDPY-4 displayed 92.54 ± 5.41%, 94.20 ± 5.50%, and 95.03 ± 5.54% antioxidant ability, respectively. BODIPY compounds showed excellent DNA chemical nuclease activity. BDPY-2, BDPY-3 and BDPY-4 also exhibited 100% APDT activity against E. coli at all tested concentrations. In addition to these, they demonstrated a highly effective biofilm inhibition activity against Staphyloccous aureus and Pseudomans aeruginosa. BDPY-4 showed the most effective antioxidant and DNA cleavage activity, while BDPY-3 exhibited the most effective antimicrobial and antibiofilm activity.

Correlation of solid-state order to optoelectronic behavior in heterocyclic oligomers

Here we address a longstanding challenge in the field of optoelectronic materials by evaluating the molecular and solid-state arrangements of heterocyclic oligomers and correlating their crystal structures to their optical properties.

Effect of thiophene substitution on the intersystem crossing of arene photosensitizers

Thiophene substitution gives energy level-matched S₁/T₂ states and the ISC is enhanced, which was not observed with phenyl substitution.

Green-to-Red Electrochromic Fe(II) Metallo-Supramolecular Polyelectrolytes Self-Assembled from Fluorescent 2,6-Bis(2-pyridyl)pyrimidine Bithiophene

The structure and properties of metallo-supramolecular polyelectrolytes (MEPEs) self-assembled from rigid 2,6-bis(2-pyridyl)pyrimidine and the metal ions Fe^II and Co^II are presented. While FeL1-MEPE (L1 = 1,4-bis[2,6-bis(2-pyridyl)pyrimidin-4-yl]benzene) is deep blue, FeL2- and CoL2-MEPE (L2 = 5,5'-bis[2,6-bis(2-pyridyl)pyrimidin-4-yl]-2,2'-bithiophene) are intense green and red in color, respectively. These novel MEPEs display a high extinction coefficient and solvatochromism. Ligand L2 shows a high absolute fluorescence quantum yield (Φ_f = 82%). Viscosity and static light-scattering measurements reveal that the molar masses of these MEPEs are in the range of 1 × 10⁸ g/mol under the current experimental conditions. In water, FeL1-MEPE forms a viscous gel at 20 °C (c = 8 mM). Thin films of high optical quality are fabricated by dip coating on transparent conducting indium tin oxide (ITO) glass substrate. Optical, electrochemical, and electrochromic properties of the obtained MEPEs are presented. Green to red and blue to colorless electrochromism is observed for FeL2-MEPE and FeL1-MEPE, respectively. The results show that the electrochromic properties are affected by the ligand topology. The Fe-MEPEs show a reversible redox behavior of the Fe^II/Fe^III couple at 0.86 and 0.82 V versus Fc⁺/Fc and display an excellent redox cycle stability under switching conditions. FeL2-MEPE in its oxidized state exhibits a broad absorption band covering the near-IR region (ca. 1500 nm) due to the ligand-to-metal charge transfer transition originating due to charge delocalization in the bithiophene spacer.

Controlled Folding, Motional, and Constitutional Dynamic Processes of Polyheterocyclic Molecular Strands

General design principles have been developed for the control of the structural features of polyheterocyclic strands and their effector-modulated shape changes. Induced defined molecular motions permit designed enforcement of helical as well as linear molecular shapes. The ability of such molecular strands to bind metal cations allows the generation of coiling/uncoiling processes between helically folded and extended linear states. Large molecular motions are produced on coordination of metal ions, which may be made reversible by competition with an ancillary complexing agent and fueled by sequential acid/base neutralization energy. The introduction of hydrazone units into the strands confers upon them constitutional dynamics, whereby interconversion between different strand compositions is achieved through component exchange. These features have relevance for nanomechanical devices. We present a morphological and functional analysis of such systems developed in our laboratories.

Insights into the effect of ketylimine, aldimine, and vinylene group attachment and regiosubstitution on the fluorescence deactivation of fluorene

The spectroscopic and electrochemical properties of a 9-substituted fluorene ketylimine (3) were investigated and compared with those of its vinylene analogue (4) to determine the origins of the quenched fluorescence of these compounds. The predominate mode of singlet excited state deactivation of the heteroatomic fluorene was found to be internal conversion involving bond rotation. Meanwhile, its carbon counterpart was found to undergo deactivation preferentially by intersystem crossing to form its triplet, which was confirmed by laser flash photolysis. Both 3 and 4 quenched the fluorescence of fluorene with diffusion-controlled rate constants, implying that the singlet excited states of 3 and 4 are also quenched by intramolecular photoinduced electron transfer (PET). This deactivation mode was found to be exergonically favorable (–90 kJ/mol for 3 and –81 kJ/mol for 4) according to the Rehm–Weller equation. The position of the heteroatomic bond on the fluorene moiety was further found to influence the singlet excited state deactivation pathway. The 2-substituted regioisomer decayed predominately by intramolecular PET and its fluorescence can be restored by acid protonation. Conversely, the PET mechanism is a minor deactivation mode for the 9-substituted fluorene derivative and its fluorescence can be enhanced by suppressing bond rotational modes, possible at low temperature and potentially in thin films.