Amphiphilic benzothiadiazole–triphenylamine-based aggregates that emit red light in water

Abstract

In this study, we report a preparation and an aggregate emission behavior of an amphiphilic donor-acceptor dye, which is composed of a triphenylamine-benzothiadiazole donor-acceptor chromophore and two water-soluble hexa(ethylene glycol) chains. The dye is strongly fluorescent in nonpolar solutions such as cyclohexane and toluene, whereas the emission intensity is reduced in aprotic polar solutions such as DMF and acetonitrile. This fluorescence reduction correlates with the increase in polarity, by which the transition from a local excited state to a highly polarized excited state is facilitated, leading to an increased nonradiative deactivation rate. Furthermore, significant fluorescence quenching is observed in protic polar solutions such as ethanol and methanol. Hydrogen-bonding interactions between the dye and the protic solvent molecules further accelerate the deactivation rate. In contrast, in a water solution, red light emission is achieved distinctly at 622 nm with a relatively large fluorescence quantum yield of 0.20. This red emission is related to the aggregation of the dye molecules grown in water. The kinetic analysis from the fluorescence rate constant and nonradiative rate constant indicates that the nonradiative deactivation channel is restricted in water. The formed aggregate, which was indicated by transmittance electron microscopy as a spherical aggregate morphology with a diameter of 3-4 nm, provides a less polar hydrophobic space inside the aggregate structure, by which hydrogen-bonding and the subsequent quenching are restricted, leading to the reduction of the nonradiative deactivation rate.

pH‐Responsive Fluorescence Change Based on Dynamic Exchange between Emitting Aggregates and Quenching Monomers in Donor–Acceptor Dyes Bearing Carboxylic Acid Groups

“…Thus, the pH‐responsive fluorescence change is attributed mainly to the changing radiative path. The lifetime decreasing and radiative path facilitation behaviors found in the aggregation of 6 molecules do not coincide with the previous finding for the triphenylamine‐benzothiadiazole dye, which indicates lifetime increasing and nonradiative path restriction upon the aggregate formation . Probably, the anionic carboxylate moiety formed in the monomer state affects the mechanism for the aggregate emission and monomer quenching.…”

“…One plausible explanation is a change of the aggregate morphology from loose packing at higher pH to tight packing at lower pH. In the tight packing, an intermolecular interaction between parent chromophore and carboxylic acid moieties is favored to facilitate the fluorescence quenching . Actually, the aggregate sizes were different at low and high pH (Figure ), suggesting the change of aggregate morphology.…”

“…Gel permeation chromatography (GPC) was performed using a Japan Analytical Industry Co., Ltd LC‐918 with a combination of JAIGEL‐1H and JAIGEL‐2H (20 × 600 mm) columns eluting with chloroform at a rate of 3.0 mL min –1 . Compounds 1 and 4 were prepared according to the methods reported previously …”

Triphenylamino α‐Cyanovinyl‐ and Cyanoaryl‐Based Fluorophores: Solvatochromism, Aggregation‐Induced Emission and Electrochemical Properties

“…The same trend was also observed for compounds 11 a and 12 . Generally, the AIE of donor–acceptor dyes is attributed to the restriction of excited‐state polarization, in addition to the restriction of intramolecular rotation . These results indicate that the combination of electron donors and acceptors is a promising approach to generate AIE‐ICT luminogens with efficient solid‐state emissions and tunable emission colors for organic light‐emitting diode (OLED) applications.…”

Synthesis, DNA Interaction and Genotoxic Evaluation of a Photoactive Benzothiadiazole with Potential Application in Photovoltaic Paint

“…19,20 In this sense, different polymers, small molecules, oligomers and hybrid compounds have been investigated for optoelectronic applications. 21 In this context, compounds that contain the electron acceptor 2,1,3-benzothiadiazole as the central unit bound to electron donors [22][23][24][25][26][27][28][29] are of great interest for the development of photovoltaic devices because of their potential use in the production of flexible polymeric films 30 that can be processed on a large scale. In addition, these π-conjugated compounds exhibit good intramolecular charge transfer, thereby reducing the band gap, 3,18,31 which is a requirement for the application of these derivatives as pigments in photovoltaic paints.…”