Combined experimental and computational studies on the photophysical properties of systematically substituted polypyridyl based ligands on a benzene core

Abstract

• Investigated dendritic systems show interesting solvent modulated photophysics; • Inter-chromophoric interaction is present in highly substituted systems; • Theoretical calculation results support the experimental observations; • Strongly modulated photochemistry of L1 and L2 in lower DMSO fraction; • Can lead to design new antenna systems with bipyridyl chromophores on benzene core. Photophysical behavior of ligands containing systematically substituted 2,2′-dipyridylamine (DPyA) chromophores on a benzene core was studied by steady-state and time resolved fluorescence experiments in combination with density functional theory (DFT) calculations. All the investigated derivatives show significant solvent modulated photophysical properties. The redshift along with the broadening in fluorescence spectra in polar protic environments could be explained by the formation of extensive solvent hydrogen bonding network with the investigated compounds. On the other hand, extremely low fluorescence yield in aqueous medium is mostly due to the significant drop in radiative deactivation pathway. In addition to the polarity outcome, the contribution of specific interactions like solvent hydrogen bond formation towards the spectral properties were examined by multi-parametric linear regression analysis using Kamlet-Taft (KT) and Catalán formalisms. While the mono and di-substituted systems ( L1 and L2 , respectively) show almost similar excited state deactivation parameters, additional interchromophoric interaction is predicted in the tri-substituted derivative ( L3 ). The experimental results were verified with TDDFT studies on isolated as well as micro-solvated ligand-water complexes.