Synthesis of novel viscosity sensitive pyrrolo-quinaldine based styryl dyes: Photophysical properties, electrochemical and DFT study

We have synthesized two novel styryl dyes namely (E) 2-(2-(9 butyl 9H carbazol-3-yevinyl)-3,3,8-trimethyl-3H-pyrrolo[3,2-h]quinoline (PQC) and (E) 10 butyl 3 (2 (3,3,8-trimethyl-3H-pyrrolo[3,2-h]quinolin-2-yl)vinyl)-10H-phenothiazine (PQPT). These dyes were characterized by FT-IR, HR-MS, H-1 and C-13 NMR spectroscopy techniques. Both dyes displayed absorption wavelength within the range of 399 - 427 nm. Ranging from non-polar solvents towards polar solvents, these dyes exhibited emission wavelength and Stokes shift from 487 - 605 nm and 85 -180 nm respectively. The photophysical study of these dyes in seven solvents suggested that these dyes show positive emission solvatochromism which was investigated from Reichardt's E-T(30) plot, Lippert-Mattaga graph and MacRae solvent polarity scale plots. In addition, these dyes show evidence of intramolecular charge transfer properties which were explained with the assist of Wellers, Rettig plots and ground-excited states dipole moment difference. The electrochemical properties of these dyes were investigated with the help of cyclic voltammetry and differential pulse voltammetry. Viscosity sensitivity studies were also performed on the synthesised dyes in the methanol and polyethylene glycol 400 system with varying viscosity of the solvent system. The thermal properties of these dyes were investigated using TGA and DSC analysis, which shows that dyes were thermally stable up to 200 degrees C. The theoretical photophysical properties of these dye molecules was explored by density functional theory (DFT) along with the time dependent density functional theory (TD-DFT).