Molecules are synthesized through multi-step organic synthesis followed by in-depth structural characterization (various NMR and mass spectrometry). Optical characterization are performed by UV/Vis absorption, steady state fluorescence, lifetimes and quantum yields, temperature-dependent fluorescence and redox characterization are performed by cyclic voltammetry and spectroelectrochemistry. Furthermore, the utility of these functional materials for sensing, bioimaging, optoelectronics and photocatalysis are being explored.
A. Light harvesting FRET Systems and Macrocycles for Multifunctional Sensing and Photocatalysis:
Multi-stimuli responsive red-green-blue (RGB) light harvesting antennae were designed and synthesized by azide alkyne cycloaddition reaction based on three different chromophores, that exhibited Förster resonance energy transfer (FRET). These antennae could ratiometrically sense temperature, pH and multiple metal ions and serve as electrochromic smart materials. We also explored covalent metal-free FRET macrocycles of [1+1] and [2+2] type consisting of PDI and aza-BODIPY chromophores that showed responsiveness towards redox potentials, temperature and metal ions. We are at present utilizing these and newer macrocycles for various NIR photocatalytic organic reactions which is an emerging research domain.
B. Molecular Rotors and Twisted D-A systems for Thermally Activated Delayed Fluorescence (TADF):
Molecular rotors where multichromophoric rotors based on BODIPY dyes as electron acceptors and benzodithiophene (BDT) as electron donors were synthesized. These rotors exhibited intriguing twisted intramolecular charge transfer (TICT) behavior resulting in large Stokes shift of up to ~ 220 nm. Furthermore, based on the regioisomers of related compounds, important structure-property correlations were deduced. Such molecules were utilized for ratiometric temperature sensing and viscosity sensing and utilized for live imaging of Cancer cell line A549 and fibroblast cell L929. Our recent research has been directed to the development of twisted D-A conjugates based on diindolocarbazole donor for TADF and their utilization for energy transfer mediated photocatalysis (photoisomerization of stilbene) and electron transfer mediated photocatalysis (arylation of heteroarenes) with broad substrate scope.
C. Utilization of D-A Compounds for Photocatalytic Organic Transformations and Photocatalytic Hydrogen Evolution:
Overview of Research Activities
Conjugated A-D-A molecules for appreciable charge carrier mobilities (~ up to 10*-3 cm2/Vs) and visible light metal-free photocatalysis (oxidative condensation cyclization to synthesize benzimidazoles) have also been developed. We are also exploring some of these compounds and new molecules as well as their composites with graphitic carbon nitride and TiO2 for efficient photocatalytic hydrogen evolution.