A Computational Approach to Nontraditional Intrinsic Luminescence: Vibrationally Resolved Absorption and Fluorescence Spectra of DABCO

Recently, so-called "nontraditional intrinsic luminescence" has been reported in several macromolecular systems. Although DABCO (1,4-diazabicyclo[2.2.2]octane) is the first system in which the effect was observed, a thorough analysis of the optical properties of the molecule, which would reveal the origin of this mysterious effect, is still pending. We perform an advanced post-Hartree-Fock treatment of the low-lying electronic states of this molecule, which need to be described with care because of their pronounced Rydberg character. We take a deeper look into the low-lying electronic transitions of DABCO targeting the explanation of the complex vibronic structures of its absorption and fluorescence spectra. Two electronic states, the ¹E'(n₊3p_xy) and ¹A₂^″(n₊3p_z) states, contribute to the absorption spectrum in the 39000-46000 cm^-1 spectral range. We also reveal the spectroscopic signature of the ¹A₂^″(n₊3p_z) state. The analyses of the contributions of individual vibrational normal modes allowed the identification of those giving rise to the complex vibronic structures of the spectra. Fluorescence emission arises from the vibronic coupling of the one-photon forbidden transition between the ¹A₁^'(n₊3s) state and the electronic ground state. The spectrum, which can be interpreted in terms of populating a few vibrational normal modes, is shifted toward visible wavelengths mostly due to the forced interaction of the lone pair electrons of the two nitrogen atoms. Our work on DABCO may help to rationalize the luminescence of more complex systems containing tertiary amine groups.

Intrinsic Blue Fluorescence of 2.0G PAMAM-DCM Polymer Dots and Its Applications for Fe3+ Sensing

A typical and environment-friendly fluorescent polyamine-amine (PAMAM) features good compatibility and unique surface modification, while it is restricted by a low fluorescence property performance and an unclear fluorescence mechanism. In this work, we prepared blue fluorescent PAMAM polymer dots (PDs) via a simple hydrothermal method based on dichloromethane (DCM) and 2.0G PAMAM. The quantum yield achieved was 32.1%, which was 25 times stronger than that of 2.0G PAMAM due to the lone-pair electron leap of the amine groups, the aggregation of carbonyl groups, as well as the crosslinking induced by DCM inside the PAMAM. In addition, the fluorescent 2.0G PAMAM-DCM PDs show a great Fe3+ sensing property with the detection limit of 56.6 nM, which is much lower than the safety limits (5.36 μM) in drinking water, indicating its great potential for Fe3+ detection in aqueous media.

Development of Spirulina sea-weed raw extract/polyamidoamine hydrogel system as novel platform in photodynamic therapy: Photostability and photoactivity of chlorophyll a

The aim of this paper is to present and characterize Polyamidoamine-based hydrogels (PAA) as scaffolds to host photoactive Chlorophyll a (Chl a) from Spirulina (Arthrospira platensis) sea-weed Extract (SE), for potential applications in Photodynamic Therapy (PDT). The pigment extracted from SE was blended inside PAA without further purification, according to Green Chemistry principles. A comprehensive investigation of this hybrid platform, PAA/SE-based, was thus performed in our laboratory and, by means of Visible absorption and emission spectroscopies, the Chl a features, stability and photoactivity were studied. The obtained results evidenced the presence of two main Chl a forms, monomeric and dimeric, interacting with hydrogel polyamidoamines network. To better understand the nature of this interaction, the spectroscopic investigation of this system was performed both before and after the solidification of the hydrogel, that occurred at least in 24 h. Then, focusing the attention on solid scaffold, the ¹Chl a^⁎ fluorescence lifetime and FTIR-ATR analyses of PAA/SE were carried out, confirming the findings. The swelling and Point Zero Charge (PZC) measurements of solid PAA and PAA/SE were additionally performed to investigate the hydrogel behavior in water. Chl a molecules blended in PAA were (photo) stable and photoactive, and this latter feature was demonstrated showing that the pigment induced, when swelled in water and under irradiation, the formation of singlet oxygen (¹O₂), measured by direct and indirect methods.

Synthesis, Internalization and Visualization of N-(4-Carbomethoxy) Pyrrolidone Terminated PAMAM [G5:G3-TREN] Tecto(dendrimers) in Mammalian Cells

Tecto(dendrimers) are well-defined, dendrimer cluster type covalent structures. In this article, we present the synthesis of such a PAMAM [G5:G3-(TREN)]-N-(4-carbomethoxy) pyrrolidone terminated tecto(dendrimer). This tecto(dendrimer) exhibits nontraditional intrinsic luminescence (NTIL; excitation 376 nm; emission 455 nm) that has been attributed to three fluorescent components characterized by different fluorescence lifetimes. Furthermore, it has been shown that this PAMAM [G5:G3-(TREN)]-N-(4-carbomethoxy) pyrrolidone terminated tecto(dendrimer) is able to form a polyplex with double stranded DNA, and is nontoxic for HeLa and HMEC-1 cells up to a concentration of 10 mg/mL, even though it accumulates in endosomal compartments as demonstrated by its unique NTIL emission properties. Many of the above features would portend the proposed use of this tecto(dendrimer) as an efficient transfection agent. Quite surprisingly, transfection activity could not be demonstrated in HeLa cells, and the possible reasons are discussed in the article.

Study of the Intrinsic Fluorescence of a Highly Branched Cationic Dendrimer, Poly(Ethyleneimine) (PEI)

Poly(ethyleneimine) (PEI) is a weakly basic, synthetic, polycationic polymer, due to the presence of primary, secondary, and tertiary amino groups. The amino groups are responsible for the variety of applications of PEI (e.g., transfection, bioimaging, solar cell, etc.). Our study presents some new and reproducible methods for the quantification of molecular or mass concentration of highly branched PEI of different molecular weights (800–2000–25,000–750,000 MW PEI). In the course of the direct method, spectrophotometry and fluorometry were applied to determine the absorption and fluorescence of PEI dilution series. An increase in the MW at the same concentration produces a higher count number because of the higher number of amino groups in PEI molecules. The character of increment in fluorescence intensity is essentially different in the case of mass concentrations and molar concentrations. The increment of the fluorescence intensity related to the molar concentration is non-linear. In the case of mass concentration, the slope is linear. Moreover, their fluorescence is enhanced with the decrease in pH values. The spectrophotometry is a reliable method for measuring the quantity of PEI molecules in solution. Our data help in recognizing the detailed properties of PEI in dendrimer research.

Intrinsic Fluorescence of PAMAM Dendrimers-Quenching Studies

Intrinsic, non-traditional fluorescence of polyamidoamine (PAMAM) dendrimers that do not possess classical fluorophores has been attracting considerable interest for the last decade. Many hypotheses regarding the source of the fluorescence have appeared, but some of them are still disputable. In order to shed new light on the nature of the phenomenon, we applied quenchers that are normally used to study intrinsic fluorescence of proteins (i.e., KI, CsCl, and acrylamide). KI and acrylamide efficiently quenched steady state fluorescence of PAMAM G2, PAMAM G3, and PAMAM G4 dendrimers. Stern-Volmer plots exhibited a downward curvature that has been elucidated by heterogenous emission. We assume that there are two distinct fluorescent moieties in the dendrimer structure that are characterized by different accessibility to the quenchers.

Fluorescent Dendritic Micro-Hydrogels: Synthesis, Analysis and Use in Single-Cell Detection

Hydrogels are of keen interest for a wide range of medical and biotechnological applications including as 3D substrate structures for the detection of proteins, nucleic acids, and cells. Hydrogel parameters such as polymer wt % and crosslink density are typically altered for a specific application; now, fluorescence can be incorporated into such criteria by specific macromonomer selection. Intrinsic fluorescence was observed at λmax 445 nm from hydrogels polymerized from lysine and aldehyde- terminated poly(ethylene glycol) macromonomers upon excitation with visible light. The hydrogel’s photochemical properties are consistent with formation of a nitrone functionality. Printed hydrogels of 150 μm were used to detect individual cell adherence via a decreased in fluorescence. The use of such intrinsically fluorescent hydrogels as a platform for cell sorting and detection expands the current repertoire of tools available.

Facile one-pot synthesis of novel water-soluble fluorescent hyperbranched poly(amino esters)

Two kinds of water-soluble fluorescent hyperbranched poly(amino esters) were first synthesized by a convenient one-pot approach via the A₂ + B₃ Michael addition reaction of trimethylolpropane triacrylate and aliphatic diamines.