A Combined Experimental and Theoretical Approach toward the Development of Optimized Luminescent Carbostyrils

Abstract

The synthesis and photophysical data of new carbostyrils (quinoline-2(1H)-ones) with the longest hitherto observed absorption-and emission wavelengths are described. Introduction of 6-amino, 7-MeO, and 4-(CF 3 ) substituents enabled us to rise the absorption and fluorescence maxima up to 414 and 557 nm, respectively. Supported by semi-empirical and ab initio calculations, the 6,7-(1,4-diazine)-fused carbostyril 23b displayed absorption maxima at up to 440 nm, with quantum yields of up to 0.9 and large Stokes shifts (> 100 nm), comparable to the best coumarin chromophores known. The new fluorophore is neither pH-sensitive between pH 6 and 10 nor susceptible to O 2 quenching. At pH 3, the emitted light appears greenish-white, which arises from three different stages of protonation.Introduction. ± In contrast to the coumarins ubiquitously used as fluorescent dyes [1], less attention has been paid to the aza-analogues quinolin-2(1H)-ones (carbostyrils), probably because of their lower extinction coefficients, hypsochromic absorption maxima, and more-cumbersome tuning of photophysical properties. However, carbostyrils are, in most cases, more resistant against pH changes (ring opening) and bleaching caused by chemical or thermal tackles. Nonetheless, 7-acetamido derivatives of Carbostyril-124, which absorb at ca. 335 nm and emit near 370 nm, have found applications in fluorescence analysis, as well as in −antenna-sensitized× europium luminescence [2]. The preference of a 7-amino group as auxochrome has its origin in the corresponding highly esteemed coumarin analogues.In earlier work [3], we have investigated substituent effects in all positions of the carbostyril system, which has provided fundamental data regarding their photophysical properties. Introduction of electron-donating and electron-accepting groups at certain positions does improve their spectral and luminescent characteristics. This converged to a so-called −push-pull× model with two electron-donating substituents in positions 6 and 7, and a CF 3 group as the acceptor at C(4). As a result of these systematic investigations, we developed 6,7-dimethoxy-4-(trifluoromethyl)quinolin-2(1H)one (1), which has an absorption maximum at 370 nm, a quantum yield of ca. 0.5, and a Stokes shift of ca. 70 nm). Inspired by this promising result, we sought further improvements [4], especially to break through the visible barrier for the absorption wavelength of carbostyrils, thus opening the field for new applications, because adequately priced light-emitting diodes (LEDs) as new excitation sources at 370, 405, and 430 nm have become available [5].Apart from the desired photophysical properties, our new fluorophores should also be readily accessible by simple chemical transformations. We envisaged to synthesize

Intense White Molecular Fluorescence from Naphthoxazole‐Quinoline Derivatives

“…Thus, the development of new materials capable of emitting white light is an area of current research interest due to their potential application in lighting and displays. The materials developed so far are based in the combination of different compounds, either organic, inorganic, or hybrid, whose combined emissions cover the visible spectrum . Although a number of such materials have been described, they are invariably complex.…”

Bisquinolones as chiral fluorophores – A combined experimental and computational study of absorption and emission characteristics

“…The TDDFT procedure has proven as a reliable tool for the electronic features including absorption and emission characteristics of structurally related coumarin dyes [24]. In simple carbostyril derivatives, TDDFT calculations using AM1 geometries had given quite good agreement between computed and experimental excitation energies [3][4][5]. The situation is less satisfactory for biscarbostyrils.…”

“…Today, mainly ''carbostyril 124" (7-amino-4-methylquinolin-2(1H)-one) is known as fluorescent dye, whereas for enzymatic assays N-acylated versions of ''carbostyril 124" are used routinely. Recently, we have shown in a systematic study that suitable functionalisation of carbostyrils leads to derivatives with absorption and emission characteristics comparable to those of coumarins [3][4][5]. For example, 4-trifluoromethyl analogue 3b (Table 1) has an absorption maximum of 370 nm, an emission maximum of 440 nm, and a quantum yield of ca.…”

Synthesis, Photophysical Properties, and Antimicrobial Activity of Novel Styryl Colorants Derived from 7‐Methoxy‐1,4‐diphenethyl‐1,2,3,4‐tetrahydroquinoxaline‐6‐carbaldehyde

“…Some quinoxaline derivatives have also been explored as antidiabetic and antiallergic agents [10–12]. Pyrazolo‐[3,4‐b]quinoxaline derivatives have been reported as photoinitiators [13, 14]. Our research group has been working in synthesis of various heterocyclic fluorescent colorants.…”