Non-traditional intrinsic luminescence of amphiphilic-based ionic liquids from oxazolidines: Interaction studies in phosphatidylcholine-composed liposomes and BSA optical sensing in solution

Clickable Polymerization-Induced Emission Luminogens Toward Color-Tunable Modification of Non-Traditional Intrinsic Luminescent Polymers

Non-traditional intrinsic luminescent (NTIL) polymer is an emerging field, and its color-tunable modification is highly desirable but still rarely investigated. Here, a click chemistry approach for the color-tunable modifications of NTIL polymers by introducing clickable polymerization-induced emission luminogen (PIEgen), is demonstrated. Through Cu-catalyzed azide-alkyne cycloaddition click chemistry, a series of PIEgens is successful prepared, which is further polymerized via reversible addition-fragmentation chain transfer (RAFT) polymerization. Interestingly, after clickable modification, these monomers are nonemissive in both solution and aggregation states; while, the corresponding polymers exhibit intriguing aggregation-induced emission (AIE) characteristics, confirming their PIEgen characteristics. By varying alkynyl substitutions, color-tunable NTIL polymers are achieved with emission wavelength varying from 448 to 498 nm, revealing a series of PIEgens and verifying the importance of modification of NTIL polymers. Further luminescence energy transfer application is carried out as well. This work therefore designs a series of clickable PIEgens and opens a new avenue for the modification of NTIL polymers via click chemistry, which may cause inspirations to the research fields including luminescent polymer, NTIL, click chemistry, AIE and modification.

Ratiometric pH Sensing, Photophysics, and Cell Imaging of Nonaromatic Light-Emitting Polymers

Here, four nontraditional fluorescent polymers (NTFPs) of varying N,N-dimethyl-2-propenamide (DMPA) and butyl prop-2-enoate (BPE) mole ratios, i.e., 2:1 (NTFP1), 4:1 (NTFP2), 8:1 (NTFP3), and 16:1 (NTFP4), are prepared via random polymerization in water. The maximum fluorescence enhancement of NTFP3 makes it suitable for ratiometric pH sensing, Cu(II) sensing, and pH-dependent cell imaging of Madin-Darby canine kidney (MDCK) cells. The oxygen donor functionalities of NTFP3 involved in binding and sensing with Cu(II) ions are studied by absorption, emission, electron paramagnetic resonance, Fourier transform infrared (FTIR), and O1s/Cu2p X-ray photoelectron spectroscopies (XPS). The spectral responses of the ratiometric pH sensor within 1.5-11.5 confirm 22 and 44 nm red shifts in absorption and ratiometric emission, respectively. The striking color changes from blue (436 nm) to green (480 nm) via an increase in pH are thought to be the stabilization of the charged canonical form of tertiary amide, i.e., -C(O^-)═N⁺(CH₃)₂, realized from the changes in the absorption/fluorescence spectra and XPS/FTIR analyses. The through-space n-π* interactions in the NTFP3 aggregate, N-branching-associated rigidity, and nonconventional intramolecular hydrogen bondings of adjacent NTFP3 moieties in the NTFP3 aggregate contribute to aggregation-enhanced emissions (AEEs). Here, structures of NTFP3, NTFP3 aggregate, and Cu(II)-NTFP3; absorption; n-π* interactions; hydrogen bondings; AEEs; and binding with Cu(II) are ascertained by density functional theory, time-dependent density functional theory, and reduced density gradient calculations. The excellent limits of detection and Stern-Volmer constants of NTFP3 are 2.24 nM/0.14234 ppb and 4.26 × 10³ M^-1 at pH = 6.5 and 0.95 nM/0.06037 ppb and 4.90 × 10³ M^-1 at pH = 8.0, respectively. Additionally, the Stokes shift and binding energy of NTFP3 are 13,636 cm^-1/1.69 eV and -4.64 eV, respectively. The pH-dependent MDCK cell imaging ability of noncytotoxic NTFP3 is supported via fluorescence imaging and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay.

Interaction Study between ESIPT Fluorescent Lipophile-Based Benzazoles and BSA

In this study, the interactions of ESIPT fluorescent lipophile-based benzazoles with bovine serum albumin (BSA) were studied and their binding affinity was evaluated. In phosphate-buffered saline (PBS) solution these compounds produce absorption maxima in the UV region and a main fluorescence emission with a large Stokes shift in the blue–green regions due to a proton transfer process in the excited state. The interactions of the benzazoles with BSA were studied using UV-Vis absorption and steady-state fluorescence spectroscopy. The observed spectral quenching of BSA indicates that these compounds could bind to BSA through a strong binding affinity afforded by a static quenching mechanism (K_q~10¹² L·mol⁻¹·s⁻¹). The docking simulations indicate that compounds 13 and 16 bind closely to Trp134 in domain I, adopting similar binding poses and interactions. On the other hand, compounds 12, 14, 15, and 17 were bound between domains I and III and did not directly interact with Trp134.