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[Display omitted] • The sensing properties of the 7-hydroxyflavone in different solvent:H 2 O mixtures were estimated. • Anion formation is the primary mechanism for the fluorescence turn-on response. • Quantum chemical calculations support the changes in spectral properties of 7HF in different environments. • Mobile phone is used to detect the water content in various food and commercial products. Fluorescence properties of 7-hydroxyflavone (7HF) have been explored in different solvents and water mixtures with steady-state and time-resolved techniques. 7HF display weak fluorescence in protic and aprotic solvents. Successive addition of H 2 O fractions induces fluorescence turn-on response accompanied by the emergence of a new green wavelength band (∼527 nm) due to the formation of anionic species and suppression of normal and hydrogen-bonded species. Jobs and ratiometric plots demonstrated the nature of complexation and fluorescence enhancement of 7HF with H 2 O in different solvents. Lower limits of detection depict the superiority of 7HF over other H 2 O sensitive systems. Time-resolved experiments help in understanding the governing parameters involved in the 7HF:H 2 O complexation. Theoretical calculations have been performed to decipher the molecular geometry of 7HF in different environments, which supports the experimental interpretations to a large extent. Hence, the present study can potentially detect a wide range of water content in organic solvents. Additionally, a practical application using a mobile phone make the system quite useful in detecting H 2 O in real and commercial samples. [ABSTRACT FROM AUTHOR]

• The ground and the excited state dipole moments of the 6-methoxyflavone were estimated from several methods. • Charge transfer mechanism is found to be the cause of larger excited state dipole moment. • Solvent dependent spectral shifts in absorption/fluorescence spectra were analyzed by multiple linear regression analysis. • This work is characterized by detailed quantum chemical studies on the nature and extent of solvent–solute interactions. The present work emphasizes on the experimental and computational analysis of the solvatochromic behavior of 6-methoxyflavone (6MF). The steady-state absorption and fluorescence spectra were observed in certain polar protic, polar aprotic and non-polar/weakly polar solvents to examine their solvatochromism and determine the electrical dipole moment. Bathochromic shift in fluorescence spectra with solvent polarity was ascribed to intramolecular charge transfer (ICT) interaction. Calculations based on various solvent correlation techniques denote that the excited singlet-state dipole moment value is higher than the ground-state counterpart, hence indicates substantial redistribution of π-electron density in the excited state. Quantum chemical investigations were performed using density functional theory (DFT) and time-dependent density functional theory (TD-DFT), respectively, in vacuum and solvents. The vertical transitions, along with the bright singlet states and HOMO-LUMO, were obtained from the DFT/TD-DFT calculations. The experimentally calculated ground and excited state dipole moments and different photophysical parameters adequately reflect the values obtained from computational methods. Multiple linear regression (MLR) method based on Kamlet-Taft and Catalan solvent parameters demonstrate that the photophysical behavior of 6MF is attributed to both specific and non-specific solute-solvent interactions. Thus, the study helps to demonstrate the sensing ability of 6MF towards organic solvents and the charge transfer/hydrogen donor/acceptor properties of complex systems. [ABSTRACT FROM AUTHOR]

• Dual fluorescence bands are observed for 5AQ in aqueous solution. • Fluorescence of 5AQ is enhanced in the presence of Ag+ ions in a purely aqueous environment. • FL enhancement of 5AQ occurs due to the dominance of the CT, inhibition of non-radiative pathways and hydrogen bonding. • 5AQ displays good selectivity for Ag+ ion over other metal ions. • 5AQ can perform as an INHIBIT logic gate. The effect of silver ions (A g +) on the photophysical behavior of 5-aminoquinoline (5AQ) has been studied in an aqueous environment using steady-state and time-resolved spectroscopic techniques. 5-AQ exhibits two weak fluorescence (FL) bands in an aqueous medium. The successive addition of A g + ions to the aqueous solution of 5AQ amplify the FL intensity of the large Stokes shifted band upto 21 folds accompanied by a red-shift as a result of the acceleration of charge transfer (CT) process and restriction of hydrogen bonding in the excited state. 5AQ exhibits good selectivity for A g + ion over other metal ions (Li+, K+, Pb2+, Zn2+, Fe2+, Mn2+, Mg2+, Cu2+, Cd2+, Co2+, Cr3+, Ni2+). The Benesi-Hildebrand and Hills equations together with DFT calculations demonstrated the formation of 1:1 complex between 5AQ and A g +. Furthermore, 5AQ can perform as an INHIBIT logic gate triggered by A g + and H + ions. Hence, the proposed study appears to be interesting in the detection of Ag+ ions in aqueous media to a certain extent, indicating that 5AQ would have potential applications in the environmental and biological monitoring of A g + ions. Additionally, practical application carried out indicates that 5AQ can be used for the recognition of Ag+ ions in drinking water samples. [ABSTRACT FROM AUTHOR]