Coumarin and Hydroxyl Decorated Viscosity Sensitive Triphenylamine Derivatives: Synthesis, Photophysical Properties, Viscosity Sensitivity, TD‐DFT, and NLO Properties

Three novel hydroxyl substituted and triphenylamine sidearm coumarin decorated molecules were prepared to examine the effect of adjacent hydroxyl substituent as well as coumarin units on the photophysical linear and nonlinear optical properties. Both hydroxyl function adjacent to the phenyl ring and extra coumarin unit is attributed to the red shifted absorption (435‐487 nm) and emission (496‐578 nm) compared to the plain triphenylamine based coumarin derivatives. Positive solvatochromism around 70 nm was observed in solvents with different polarity polarities and it is reinforced by solvent polarity plots and multilinear regression study. Very high viscosity induced emission enhancement (5.7 – 8.2 fold) was observed for in ethanol/polyethylene glycol‐400 system, highlighting their capability to act as efficient fluorescent molecular rotors (FMRs). The nonlinear optical properties were investigated by solvatochromism as well as a computational method using B3LYP 6–311++G (d, p) basis set. All these compounds exhibited large magnitudes of first order (65‐208x10 −30e.s.u) and second order (560‐2120x10 −36e.s.u) hyperpolarizability. Coumarin decorated hydroxy derivatives with monoand dihydroxy monocoumarin and dicoumarin were synthesised which shows good solvatochromism, viscosity sensitivity with 8.2 fold increase in emission intensity, and high NLO properties. Charge transfer observed in all the compounds were well studied and supported by solvent polarity plots and charge transfer characteristics were elucidated by using MH analysis and HOMO‐LUMO energy band gap.