Regioisomeric acceptor‐donor (AD) molecular rotors (p‐AD, m‐AD and m‐ADA) were synthesized and characterized, wherein dyads p‐AD and m‐AD, and triad m‐ADA contained 4,4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BODIPY) and benzodithiophene (BDT) as electron‐acceptor and electron‐donor, respectively. In all the compounds, the donor and acceptor moieties are electronically decoupled by a phenyl spacer, either through a para coupling or through a meta coupling. The dyad counterparts p‐AD and m‐AD showed distinct photophysical characteristics in which dyad p‐AD showed TICT band at ca. 654 nm characterized by a Stokes shift of ca. 150 nm and prominent solvatochromism. However, meta regioisomeric triad m‐ADA showed well‐defined aggregation in solution. Notably, because of the temperature‐tunable and solvent‐viscosity‐dependent emission, efficient ratiometric temperature sensing with positive and negative temperature coefficients and viscosity sensing was observed for all compounds. Interestingly, the fluorescence of dyad m‐AD (in 10/90 v/v THF/water) revealed a near‐white light emission with CIE chromaticity coordinates (x, y) of (0.32, 0.29). Furthermore, the fluorescence emission of p‐AD in THF at 0 °C also showed a near‐white light emission with chromaticity coordinates (x, y) of (0.34, 0.27). Such multifunctional rotors with readily tunable emission in the red region and prominent temperature‐ and viscosity‐sensing abilities are promising for sensing and bioimaging applications.

Three non-fused AÀ DÀ A'À DÀ A π-conjugated metalfree small molecules BT-IT1, BT-IBT2 and BT2F-IBT3 have been synthesized and their absorption characteristics and redox properties, as well as charge carrier mobilities have been investigated. The resultant molecules exhibited broad absorption in the range of 325-600 nm in solutions and in thin films the absorption range is 350-700 nm. These new conjugated small molecules showed low-lying HOMO energy levels (À 5.49 to À 5.50 eV), deep LUMO energy levels (À 3.67 to À 3.69 eV) and narrow bandgaps of (E g CV ) ~0.79 eV. Appreciable electron mobilities for compounds BT-IBT2 and BT2F-IBT3 were 4.56 × 10 À 3 and 1.12 × 10 À 3 cm 2 V À 1 s À 1 , respectively, obtained by space-charge limited current (SCLC) measurements. Additionally, excellent photocatalytic performances of BT-2T (6), BT2F-2T (10), BT-IT1, BT-IBT2 and BT2F-IBT3 for highly selective oxidation of thioanisole to desired sulfoxides under visible light irradiation were observed.

Recently developed C10‐(H)‐arylated‐N‐(pyren‐1yl)‐picolinamide compounds have been investigated spectroscopically for their photophysical properties and metal ion sensing abilities. Two sets of regioisomers were selected based on their molar absorptivities and fluorescence quantum yields and classified into two series I methoxy group at meta‐ and para‐ position of phenyl ring, and series II methyl group at meta‐ and para‐ position of phenyl ring. Additionally, for better understanding on structure‐property relationship, a comparison study with C‐10 unsubstituted compound was also conducted. All compounds exhibited characteristic absorption and emission responses only towards Cu2+ and Fe3+ ions among all the screened metals. While the reference compound and those with methoxy substituent displayed a fluorescence turn‐off behaviour, compounds with methyl groups showed fluorescence turn‐on response through excimer formation at ∼550 nm in the presence of Cu2+ and Fe3+. Sensing studies were performed to elucidate structure‐property relationship and to obtain limits of detection, binding constants and fluorescence quenching constants. Temperature‐dependent fluorescence studies were performed to distinguish the type of excimers produced by two compounds in series II with the metal ions.