Coumarin and its derivatives have potential applications in sensing, laser dyes, fluorescent probes, and dye sensitized solar cells due to their unique photophysical properties. However, synthesis and studies of linear pyridine-fused-π-extended coumarins remained unexplored. Here, we synthesised two π-expanded coumarin derivatives (PC1, PC2) in which molecular backbone is linearly extended with pyridyl ring where 5,7-positions are substituted with aryl groups. Single crystal X-ray structure analysis confirmed the molecular geometry. We found in spectroscopic studies that both coumarins in solutions show fluorescence via predominant radiative decay of charge transfer (CT) state due to rotational motion associated with the molecules. In addition, detailed spectroscopic analysis of both coumarins in presence of acid and base revealed the acidochromic property in solutions. Based on the acid-base sensing property of PC1, we could show its use as solid-state acid-base vapor sensor and anti-counterfeiting agent. © 2020

Debdas Ray

Chemistry

(SoNS) School of Natural Sciences

Karmakar S.

<p>Shiv Nadar University is a comprehensive, multidisciplinary, research-focused, and student-centric University offering a full range of academic programs at the undergraduate, postgraduate and doctoral level. With state-of-the-art infrastructure, the University comprises of academic wings, sophisticated labs, international standard sports facilities, amphitheaters, auditorium, conference rooms and smart classrooms. The University&rsquo;s goal is to become internationally recognized for the quality of its research and creative endeavors and their applicability to improving quality of life, generating new insights and expanding the boundaries of human knowledge creativity. Committed to excellence in teaching, research and service, the University aims to serve the higher education needs of India and the world beyond.</p>

Shiv Nadar University

Journal of Luminescence

The influences of naphthyl and/or phenyl rings at the 2,4-positions of the quinolinyl fragments in carbazole-quinoline conjugates are studied. The centric phase of one of the conjugates (β-CQNN) revealed both thermally activated delayed fluorescence (TADF) and room-temperature phosphorescence (RTP), while prompt fluorescence and RTP were observed in the non-centric phase (α-CQNN) that can regenerate the emission features of β-CQNNvia mechanical grinding. This unique observation is explained by the modulation of the higher-lying triplet (T2) energy level caused by conformational change. © The Royal Society of Chemistry.

Fulltext

Chemical Communications

Thermally activated delayed fluorescence and room-temperature phosphorescence in naphthyl appended carbazole-quinoline conjugates, and their mechanical regulation

Achieving red phosphorescence from purely organic system is a challenging feat due to the predominant thermal nonradiative decay pathways of the excited electrons. Here, we design single-component charge-transfer (CT) complexes based on phenoxazine-quinoline conjugates (PQ1-PQ3), in which the phenoxazine ring is covalently attached to the quinolinyl fragment via a C-N bond. These conjugates in concentration-dependent absorption studies show a new low-energy CT absorption band along with the parent Ï€-Ï€∗ band with binding constants of up to 102 M-1 due to self-association via intermolecular CT (I2CT). Steady-state emission and phosphorescence decay transient measurements of all of the conjugates in solutions, thin films, and crystals reveal the signature of I2CT that leads to orange-red phosphorescence (ORP) at ambient conditions. Theoretical calculations show the existence of dimer with stronger I2CT characteristics and reduced energy gap between the lowest singlet (S1) and triplet (T1) states (Î"EST = 0.05-0.14 eV), which is in line with emission measurements. These conjugates are used for solid-state dichloromethane vapor sensors, and PQ3 can be transformed into oxygen sensor. These studies give an insight into the ORP properties and provide a rational strategy for the design of single-component self-CT complexes with ORP feature at ambient conditions. © 2018 American Chemical Society.

Journal of Physical Chemistry C

Roomerature Orange-Red Phosphorescence by Way of Intermolecular Charge Transfer in Single-Component Phenoxazine-Quinoline Conjugates and Chemical Sensing

Methoxyethoxy-substituted coumarin-benzimidazole: Substituent group positions adjusted the self-assembly, optical properties and ions sensor

We report the synthesis and photophysical properties of a coumarin based probe (1E)-1-(1-(7-(diethylamino)-2-oxo-2H-chromen-3-yl) ethylidene) thiosemicarbazide (DIDOT). DIDOT shows a polarity dependent change in the emission maxima in the solution phase. This is explained by the increased dipole moment in the excited state by an intramolecular charge transfer (ICT) process. DIDOT can successfully detect Zn(ii) in aqueous methanol by a shift in the charge transfer emission maxima from approximately 506 to approximately 535 nm. This shift led to a change in the color of the emission from green to yellow under UV-light. The mechanism of Zn(ii) detection has been delineated using electrospray ionization-mass spectrometry (ESI-MS), Fourier-transform infrared spectroscopy (FTIR) and fluorescence time resolved studies coupled with theoretical calculations. The increment in the charge transfer in the Zn(ii) complex of DIDOT over the bare receptor as a consequence of conformational locking was determined to be the underlying cause of the cation detection phenomenon. The limit of detection and binding constant values of DIDOT towards Zn(ii) were approximately 3 × 10-8 M and 2.35 × 105 M-1 respectively. Finally, the practical utility of DIDOT has been demonstrated by successful detection and quantification of Zn(ii) in spiked water samples. © 2019 The Royal Society of Chemistry and Owner Societies.

Photochemical and Photobiological Sciences

Evaluating the merit of a diethylamino coumarin-derived thiosemicarbazone as an intramolecular charge transfer probe: Efficient Zn(II) mediated emission swing from green to yellow