Linear Optical and Third-Order Nonlinear Optical Properties of Some Fluorenyl- and Triarylamine-Containing Tetracyanobutadiene Derivatives

The synthesis and characterization of four new tetracyanobutadiene (TCBD) derivatives (1–3 and 2′) incorporating 2- or 2,7-fluorenyl and diphenylamino moieties are reported. The electroactivity of 1–3 and 2′ was studied by cyclic voltammetry (CV), while the linear optical and (third-order) nonlinear optical (NLO) properties were investigated by electronic spectroscopy and Z-scan studies, respectively. All experimental investigations were rationalized by DFT computations, providing an insight into the electronic structure of these derivatives and on their application potential. We show that these derivatives are nonluminescent in solution at ambient temperatures, but become fluorescent in solvent glasses. This finding constitutes an unprecedented observation for TCBD derivatives. Also, we show by Z-scan studies that these derivatives behave as two-photon absorbers in the near-IR range (800–1050 nm). These third-order NLO properties are discussed and compared with those of their alkynyl precursors (4–6), which have been investigated by two-photon excited fluorescence (TPEF).