Multipolar triphenylamines: Effect of spectator donor-acceptor pair on intramolecular charge transfer interactions. (January 2020)

• Record Type: Journal Article
• Authors: Thamaraiselvi, Pichandi; Varathan, Elumalai; Subramanian, Venkatesan; Easwaramoorthi, Shanmugam
• Is Part Of: Dyes and pigments. Volume 172(2020)
• Publication Date: 2020-01
• Subjects: Triphenylamine -- Charge transfer -- Donor-acceptor system -- Solvatochromism -- Symmetry broken dipolar CT; Dyes and dyeing -- Periodicals; Pigments -- Periodicals; 667.2
• DOI: 10.1016/j.dyepig.2019.107838
• Languages: English
• ISSNs: 0143-7208

Abstract

Abstract: Donor (D) - Acceptor (A) compounds based on triphenylamine (TPA) substituted with cyano, nitro, and formyl functional groups were synthesized in dipolar (DA), quadrupolar (DA2 ), and octupolar (DA3 ) configurations and characterized using different spectral techniques. Bond-length alternation (BLA) values of the phenyl ring were found to be in the range between 0.012 and 0.022 Å, suggest the charge transfer occurs in the ground state itself, which in fact differs distinctly with respect to number of acceptor groups in the TPA core. Steady-state and time-resolved fluorescence studies indicates the existence of dipolar charge transfer interactions in all the molecules by the virtue of reducing their molecular symmetry. Interestingly, for dipolar molecule, the efficiency of ICT interactions is elucidated by the slope of the Lippert-Mataga plot which exhibits the linear relationship with the Hammett (σ) constant. Controlling the rotation of N–C bond of amino and phenylene moiety by lowering the surrounding temperature drastically affect the fluorescence and reveals that the structural changes at the excited state plays a crucial role in ICT processes. Notably, the mono-nitro substituted triphenylamine exhibits specific solvent-solute interactions exclusively with the chlorinated solvents at the excited state with the emission in NIR region and is tailing over 800 nm. Graphical abstract: Image 1 Highlights: 1. Donor-Acceptor chromophores in dipolar, quadrupolar, and octupolar configuration without changing the core structure have been developed using triphenylamine and cyano, formyl, and nitro groups. 2. Excited state symmetry breaking occurs in quadrupolar and octupolar molecules and forms dipolar charge transfer states. 3. The strength of the intramolecular charge transfer interactions might be correlated with the Hammett (σ) constant. 4. Nitro substituted triphenylamine derivatives exhibit specific solvent-solute interactions with the chlorinated solvents.