Design and Synthesis of D--A form of p-Nitrophenylacrylonitrile Substituted Triphenylamine Chromophores; Photophysical, Electrochemical Properties, DFT and Thermal Studies

This paper reports a novel Donor-pi-Acceptor type of pi-conjugated triphenylamine (TPA) dyes bearing a 4-nitrophenyl acrylonitrile units (abbreviated as TPA-4(a-e) which were synthesized by Knoevenagel condensation followed by palladium catalyzed Suzuki-Miyaura cross coupling reaction with good yield. These dyes contain TPA as electron donor (D) and 4-nitrophenyl acrylonitrile as electron acceptor (A) and probes were confirmed by standard spectroscopic techniques viz.,H-1, C-13 NMR, FT-IR, GC-MS and ESI-MS. Herein, for the D-pi-A push-pull structure, TPA and 4-nitrophenyl acrylonitrile are connected by vinylene bond as the pi-bridge. Optical/Solvatochromic properties were studied in detail by UV-Vis absorption and fluorescence spectroscopy. The intramolecular charge transfer properties were studied using DFT model with the CAM-B3LYP function and solvatochromism by experimental method. The synthesized materials have shown moderate quantum yields. Optical bandgap values range from 2.33 to 2.39 eV and these derivatives exhibit well judged thermal stability and their 5 % weight loss temperature are in the range 178-220 degrees C. Cyclic voltametery study of the title compounds indicated that Eoxonset values ranging from 1.05-1.25 eV. Quantum yields (phi) of the probes are experimentally measured in the 1, 4-dioxane and the Stokes shifts are observed to be in the range of 4882-5545 cm(-1). The results displayed that these novel (D-A-D) chromophores could play an important role in the organic optoelectronics.