Enhanced Fluorescence of Loosely Packed Dye Aggregates

Abstract

The fluorescence of a hemicyanine dye was considerably enhanced by the formation of loosely packed aggregates, compared to tightly aggregated and molecularly dispersed hemicyanine dyes. Loose dye aggregates were realized by introducing a self-assembling unit to the dye molecules and by adjusting the mixture of good solvent and nonsolvent for the dye moiety.The aggregation morphology of organic dyes can greatly affect their fluorescence intensity, wavelength, and lifetime. For example, when arranged in a parallel orientation, the so-called H-aggregation generally causes a significant decrease in fluorescence intensity accompanied by a blue shift of the absorption band with respect to the monomer band.1 Conversely, in a slipped arrangement, the so-called J-aggregation exhibits a narrow red-shifted absorption band which often results in enhanced fluorescence with a very small Stokes shift.1 Therefore, how dye molecules are designed and the way in which their aggregation morphology is controlled are very important for applications of fluorogenic materials (for example, sensors, laser sources, sensitizers, and nonlinear optical materials).Fluorescent dyes are very useful materials and are usually used in solution at low concentration so that the dye molecules do not form aggregates and self-quench. In contrast, a number of dyes have recently been developed that exhibit strongly enhanced fluorescence by the formation of rigid aggregates in the solid (nanoparticles and thin films) 1a,2 or gel 3 states, through a process known as aggregation-induced emission (AIE). This finding has expanded the range of fluorogenic dye applications. Their enhanced fluorescence is caused by, for example, conformational planarization, J-aggregate formation, and physical constraint. The formation of tightly packed dye aggregates has been limited to the solid state or at sufficiently high solution concentrations at which gel formation can occur.In this paper, we demonstrate the fluorescence enhancement of a hemicyanine (stilbazolium) dye based on a new concept, that is, the formation of "loosely packed aggregates" in the sol state. In general, it is difficult to form such loose aggregates in the solution state because dyes can be molecularly dispersed in good solvents, whereas tightly packed dye aggregates are formed in poor-or nonsolvents. We have achieved the formation of loose dye aggregates by functionalizing the dye molecule with an

Synthesis and Characterization of Porphyrin-Based GUMBOS and NanoGUMBOS as Improved Photosensitizers

“…Fluorescence spectra of the TCPP compounds depicted two bands, which are consistent with literature studies for free base porphyrins (Figure B). , Both bands contained in the fluorescence spectra of TCPP nanoGUMBOS were red-shifted and displayed enhanced fluorescence intensity as compared to that of the parent dye. Fluorescence enhancement in nanoGUMBOS samples was attributed to formation of loosely packed dye aggregates which were produced by the presence of bulky and long alkyl chain phosphonium cations . Furthermore, fluorescence spectra of the nanoGUMBOS were better resolved as compared to the parent dye showing two distinct bands belonging to Q­(0,0) and Q­(0,1).…”

“…Fluorescence enhancement in nanoGUMBOS samples was attributed to formation of loosely packed dye aggregates which were produced by the presence of bulky and long alkyl chain phosphonium cations. 31 Furthermore, fluorescence spectra of the nanoGUMBOS were better resolved as compared to the parent dye showing two distinct bands belonging to Q(0,0) and Q(0,1). NanoGUMBOS formed by use of the ion association method at a molar ratio of 1:1 exhibited fluorescence spectral shapes that contained characteristics of both nanoparticles composed of loosely packed aggregates and the monomer.…”

Understanding a Thermoemissive ESIPT-Based Solid-State Off–On Switch as a Dual-Channel Chemosensor in Solid and Solution Phases: Detailed Experimental and Theoretical Study

“…Also, over the long past, Schiff bases are recognized as efficient tools for the application of molecular sensors, nonlinear optics, and molecular switches for optical detection. , Keto–enol tautomerism is very common in Schiff bases having an alcoholic −OH group in the close vicinity in solution, but it is rather scarce in the solid phase. − In the course of keto–enol tautomerism, intramolecular H-bonding plays a decisive role in exhibiting thermochromism and photochromism in the solution phase. − In general, intramolecularly H-bonded cis -enol forms are more stable than the cis -keto forms in the ground states, but the cis -keto form remains stabilized with the rapid proton transfer known as keto–enol tautomerism in the excited states, which is mainly governed by the electronic environment of the imine group and the donor atom adjacent to it. , Thus, in most of the cases reported to date, the cis -keto form was found to be more stable in the excited states at room temperatures in keto–enol tautomerism. , However, this stabilization is strongly dependent on the nature and polarity of the solvents used. Generally, the cis -enol form is more stable in nonpolar solvents and the corresponding keto form in polar solvents. − Moreover, J- or H-type aggregation becomes promising due to the cis-arrangement, which in turn makes the molecule rigid to rotational or vibrational motion. , This restriction of motion resulted in the radiative decay of energy and ultimately strong fluorescence in solid and solution or aggregate state. − …”

“…Although the excited-state intramolecular proton transfer (ESIPT) phenomenon is of wide interest due to its stimulating photochemical and photophysical applications, the thoughtful insight of the equilibrium between cis- enol and cis -keto and then to trans -keto form in the solid phase upon heating has not been available thus far with in-depth interpretation both theoretically and experimentally. − Yet again, dual-channel sensing of cations of biological importance like Al 3+ and Zn 2+ is important, and a considerable amount of work has been done in this respect in the solution/aqueous phase. Simultaneous detection of multiple analytes is important for the selective and sensitive probe as these save time, cost, and effort.…”

Multi-chiro-informative System Created by a Porphyrin-functionalized Chiral Molecular Assembly

“…5,7 We prepared G-Por by coupling synthesized N 2 ,N 3didodecyl-L-glutamide (G) with 5-(4-carboxyphenyl)-10,15,20triphenyl-21H,23H-porphine and subsequent insertion of zinc according to previously reported methods. 6,7 Confocal microscopy showed that a solution of G-Por in cyclohexane contains globular images, as revealed through the fluorescence of the porphyrin moiety (Figure 1b). The globular aggregation morphology is unusual given that G-derivatives often produce fibrils.…”