Concentration dependence of steady-state fluorescence behavior of a liquid crystal molecule E7 in ethanol

The fluorescence excitation and emission spectra of a liquid crystal E7 in ethanol have been explored at a variety of concentrations from very dilute solutions (<1.0×10−7 mol/L) to concentrated solutions (>1.0×10−2 mol/L) and also for neat E7. The result showed a strong dependence of the steady-state fluorescence behavior on E7 concentration in ethanol. The photophysical behavior has been interpreted in terms of short-range and long-range intermolecular interactions and ground-state molecular association as well as spectral changes of the fluorescence excitation and emission. The short-range intermolecular interaction characterized by the fluorescence emission band with the maximum between 376 and 385 nm gradually increases with increasing E7 concentration. On the other hand, the long-range intermolecular interaction characterized by the emission band with the maximum between 347 and 362 nm gradually decreases with increasing E7 concentration. Consequently, with increasing E7 concentration in ethanol the long-range interaction effect is reduced, whereas the short-range effect is enhanced and the monomer emission completely disappears at concentrations greater than 2.83×10−5 mol/L.