Spectral Characteristics of Highly Fluorescent 2-(<i>N,N</i>-dimethylamino)tryptanthrin

Abstract

We previously reported that 2-aminotryptanthrin (T2NH2) possesses excellent photophysical properties such as wide-wavelength absorption and emission in the visible region and a high fluorescence quantum yield. It also exhibits large positive fluorescent solvatochromism. In this study, we synthesized 2-(N,N-dimethylamino)tryptanthrin (T2NMe2), from which we expected a substantial bathochromic shift of the emission band to the near-infrared (NIR) region by acceleration of intramolecular charge transfer. As such, the emission maxima (f, max) of T2NMe2 in some solvents were observed in the NIR region.

Fluorescence Emission Mechanism of Three <i>N,N</i>-dimethylaminotryptanthrins by Density Functional Theory Calculations

“…It also exhibited strong positive fluorescence solvatochromism and is more strongly polarized in the excited state than the ground state. Thus, fluorescence from T2NMe2, with a strongly electron-donating dimethylamino group, was observed in the near-infrared (NIR) region (650-900 nm), which is referred to as the "optical window" of cells and tissues [11], due to ICT acceleration [10]. We can therefore conclude that T2NMe2 is potentially suitable as a fluorescent dye in the NIR region.…”

“…Tryptanthrin is a weakly basic alkaloid present in several plant species [7] and shows antimicrobial activity against diverse pathogenic bacteria and fungi [8]. When an amino group or other electron-donating substituent is introduced at the 2-position of tryptanthrin, intramolecular charge transfer (ICT) occurs between the electron-withdrawing carbonyl group at its 6-position and the amino group, resulting in strong fluorescence and positive fluorescence solvatochromism [9,10]. The fluorescence wavelengths of the fluorescent solvatochromic dyes vary according to the surrounding environment (polarity difference); thus, a variety of life phenomena can be observed via the fluorescent color change.…”

Aggregation-induced Emission Properties of 2-(<i>N,N</i>-diphenylamino)tryptanthrin

“…1a) [6] and 2-(N,N-dimethylamino)tryptanthrin (T2NMe2, Fig. 1b) [7], previously reported by us, exhibit excellent fluorescence properties; however, fluorescence quenching occurs at high concentrations owing to the presence of π-π stacking interactions favored by the planar structure of the molecules. Therefore, we envisaged that this quenching could be overcome by replacing the two hydrogens of the amino group of T2NH2 with phenyl groups.…”

“…Absorption maxima were used as excitation wavelengths of the fluorescence spectra. The fluorescence quantum yields (f) were determined at room temperature relative to that of T2NMe2 in DCM (f = 0.89) [7] using solutions with matched absorbance (0.1) at the excitation wavelength. AIE measurements were performed using THF/water mixed solutions with different THF/water ratios.…”

2-Hydroxytryptanthrin and 1-Formyl-2-hydroxytryptanthrin as Fluorescent Metal-ion Sensors and Near-infrared Fluorescent Labeling Reagents

“…The synthesis and application of fluorescent tryptanthrin derivatives are generating widespread interest in current literature [1,2,3,4,5]. These compounds absorb and emit radiations at long wavelengths and are used across diverse fields and for a variety of functions, such as in labeling reagents, chemosensors, laser dyes, photosensitizers, and fluorescent organic devices.…”