Small Iminocoumarin Derivatives as Red Emitters: From Biological Imaging to Highly Photoluminescent Non‐doped Micro‐ and Nanofibres

Abstract

The fluorescence properties of four derivatives of 3-thienyl-2-(N-dicyanovinyl)iminocoumarin, bearing a diethylamino group in the 7-position or a methoxy group in the 6, 7 and 8 positions, were compared in solution and in the solid state. The 7-diethylamino derivative was strongly fluorescent in various solvents, with marked solvatochromism. Its fluorescence was quenched by aggregation. In contrast, the methoxy derivatives were only moderately or weakly fluorescent in solution, but two of them were strongly photoluminescent in the crystalline state, owing to favourable molecular packing. The 6-methoxy derivative even exhibited spectacular crystallization-enhanced emission, examples of which are particularly rare for this type of dyes. Dyes were tested for biological use. The 7-diethylamino derivative led to particularly strong fluorescence staining of the cytoplasm of HCT-116 colon cancer cells. No fading was observed over prolonged illumination by the microscope light beam, but a phototoxic effect was detected. The use of the dyes as red-emitting materials was also investigated. Using easy-to-implement preparation methods, the compounds self- assembled to give one-dimensional nano- and microsized particles, including millimeter-long microfibres that exhibited clear wave-guiding properties. This study shows the value of these low molecular-weight molecules for the preparation of new orange and red-emitting fluorescent materials based on totally pure dye.

Green and Red Fluorescent Dyes for Translational Applications in Imaging and Sensing Analytes: A Dual‐Color Flag

“…Different strategies can be employed to ensure that coumarin derivatives have enough charge transfer in the coumarin molecule to push the absorption and emission in the red region: 1) introducing an electron donor in the 5‐ and 7‐positions; 2) introducing an electron‐withdrawing group at the 3‐ and 4‐positions; 3) increasing the rigidity of the donor and acceptor groups; and 4) extending the conjugation. Khemakhem and co‐workers show the value of using substituents with low molecular weights to prepare new orange‐ and red‐emitting fluorescent materials based on coumarin. In their work, the researchers explore the fluorescence properties of four derivatives of 3‐thienyl‐2‐( N ‐dicyanovinyl)iminocoumarin, that is, 106 – 109 , bearing a diethylamino group in the 7‐position (as in 106 ) or a methoxy group in the 6‐, 7‐, and 8‐positions (as in 107–109 ); studies have been performed both in solution, using a range of organic solvents as well as water, and in the solid state (see Figure ).…”

Detection of fluorescent organic nanoparticles by confocal laser endomicroscopy in a rat model of Barrett’s esophageal adenocarcinoma

“…The procedure used for the measurement of photoluminescence quantum yields was identical to that described elsewhere. 31 …”

Individual control of singlet lifetime and triplet yield in halogen-substituted coumarin derivatives

“…20,21 In other approaches the comparably small coumarin moiety was used to study the attached functional groups. [22][23][24] In our case the 3-substituted diethylphosphono and phosphono groups are commonly known for their enzyme inhibiting abilities. 25,26 The electron withdrawing effect of the diethylphosphono group on the conjugated aromatic coumarin structure reduces the electron density stronger on 7 with respect to 6-position.…”