Switchable sol-gel transition controlled by ultrasound and body temperature

<p>Herein, we reported a new kind of naphthalimide-based derivative (<b>N1</b>), which could undergo direct sol–gel transition accelerated by ultrasound in 2-methoxyethanol. The gels are very sensitive to the body temperature in the range from 35 to 42 °C, which is the scope range of clinical thermometer. The gel-to-sol transition temperatures enhanced with the increased concentrations of the gels. The reversible gel-sol transition, together with emission intensity and morphological changes, controlled by body temperature and ultrasound could be repeated by many circles without fatigue. Therefore, the gel could be developed to an ideal sensor for detecting human body temperature.</p

Visual Recognition of Aliphatic and Aromatic Amines Using a Fluorescent Gel: Application of a Sonication-Triggered Organogel

A naphthalimide-based fluorescent gelator (<b>N1</b>) containing an alkenyl group has been designed and characterized. This material is able to gelate alcohols via a precipitate-to-gel transformation when triggered with ultrasound for less than 2 min (S-gel). The gelation process in <i>n</i>-propanol was studied by means of absorption, fluorescence, and IR spectra, scanning electron microscopy (SEM) images, and X-ray diffraction patterns. The fluorescence intensity of <b>N1</b> decreased during the gelation process in a linear relationship with the sonication time. The S-gel of <b>N1</b> could be used to sense aliphatic and aromatic amines by measuring the change in the signal output. For example, the addition of propylamine to the S-gel of <b>N1</b> resulted in a dramatic enhancement of the fluorescence intensity, accompanied by a gel-to-sol transition. On the contrary, when the S-gel of <b>N1</b> was treated with aromatic amines such as aniline, fluorescence was quenched and there was no gel collapse. The sensing mechanisms were studied by ¹H NMR, small-angle X-ray scattering, SEM and spectroscopic experiments. It is proposed that isomerization of the alkenyl group of <b>N1</b> from the trans to cis form occurs when the S-gel is treated with propylamine, resulting in a gel–sol transition. However, the aromatic aniline molecules prefer to insert into the gel networks of <b>N1</b> via hydrogen-bonding and charge-transfer interactions, maintaining the gel state. As potential applications, testing strips of <b>N1</b> were prepared to detect aniline