1,10-Fused ring phenothiazines were found to be a new kind of fluorescent dyes that strongly fluorescence in protic solvents than in aprotic solvents, with higher fluorescence quantum yields (Φ) and longer emission wavelength than the previously reported dyes that with similar solventsensitivity profile. For example, compound 5 shows a Φ-value of 0.075 in diethyl ether and 0.517 in methanol. Interestingly, a transition from C Cdouble bond (5) to C single bond (4) in the fused ring switch the photophysical properties completely, i.e. the analogue compound 4 demonstrates the opposite sensitivity, for which Φ= 0.099 in diethyl ether but the fluorescence is quenched completely in methanol. Further derivatization of 5 is convenient, demonstrated by the preparation of compound 6, for which the unique solvent sensitivity is reserved and higherΦin protic solvents was observed (Φ= 0.739 in methanol). The solvatochromism of the compounds were analysed with Lippert–Mataga correlation, ENT (30) values and multilinear regressions with Catalán and Kamlet–Taft solvents scales. The aprotic and protic solvents appeared as two isolated domains in the Lippert–Mataga plots, whereas fitting with ENT (30) scales gives a linear regression comprising both aprotic and protic solvents. Kamlet–Taft scales are more appropriate than the Catalán solvent scales for describing the solvatofluorochromism of the compounds. An intermolecular hydrogen bonding mechanism is proposed for the observed switching of the fluorescence with protic solvents.

Fluorescent DNA probes with 1,6-hexanediyl as the linker between two pyrenes, phenylpyrenes or phenylethynyl pyrene fluorophores were synthesized (Py-1, Py-2 and Py-3) and their interactions with DNA were studied by UV–vis absorption spectra, fluorescence spectra and viscosity measurements. The probes show red-shifted emission compared with pyrene (up to 20nm). We found the interaction of these probes with DNA can be either intercalation or groove binding. Ratiometric fluorometry (ratio of the monomer and excimer emission intensity versus concentration of DNA) was achieved with these probes for DNA quantification (with limit of detection, LOD, up to 0.1g/mL). We also found that the undesired oxygen sensitivity of the emission intensity of pyrene fluorophore can be greatly suppressed by extending the π-conjugation framework of pyrene (the IAr/Iair value is decreased from 8.10 for pyrene to less than 2.20 for the DNA probes described herein).

The X-ray diffraction (XRD) studies of a coumarin based hydrazone (receptor 1) have revealed self assembled pseudo double helix architecture involving closed shell O-O interactions besides other supramolecular interactions. The receptor (1) an intramolecular charge transfer (ICT) probe detected acetate, benzoate and dihydrogenphosphate through naked-eye in DMSO. The 1:1 stoichiometry was confirmed for all the anions. The 1H NMR studies indicated classical and non-classical hydrogen bonding through- NH and Ar-H protons of the receptor, respectively, during recognition process of the acetate through receptor (1). The theoretical studies through density functional theory (DFT) using B3LYP exchange functional with the basis set 6-311G** supported the UV-vis and 1H NMR studies. The time dependent density functional theory (TDDFT) computations of UV-vis excitations for the receptor (1) and receptor-acetate complex agreed well with our experimental findings. The cyclic voltammetric studies also supported formation of receptor–acetate complex.