Research Projects

In recent years different conceptual and theoretical developments have been reported to explain the mechanism of AIE (aggregation induced emission) and/or AEE (aggregation enhanced emission) phenomena. These are restriction of intra-molecular rotation (RIR), twisted intra-molecular charge transfer (TICT), cis-trans isomerization, excited state intra-molecular proton transfer (ESIPT), restricted access to conical intersection (RACI), restriction of access to dark state (RADS) etc. Among the abovementioned mechanisms RACI seems to be the most fundamental cause of AIE (or AEE). In the RACI model, the energetically accessible conical intersection is responsible for the radiationless decay of AIEgens in solution and thus explains the lack of fluorescence in solution, but in the aggregate phase the non-radiative decay pathways are blocked due to which energy of the conical intersection increases. Thus the purpose of the proposed research proposal is to carry on in-depth study of the correlation between different types proposed mechanism of AIE (or AEE) (e.g., RIR, RIV, Anti-Kasha rule, RADS) with RACI. Also, very limited number of studies on RACI are reported using wave-function based approach (e.g., CASSCF and CASPT2), which are very much computational resource demanding as the AIE (or AEE) systems are generally large in size and excited state optimization as well as relaxed scans of potential energy surfaces (PES) are needed to verify existence of RACI. So, in the proposed project photophysical properties will be computed by TDDFT methods (along with some wave-function based approach for comparison) after non-empirically optimal tuning of range separated hybrid (RSH) functionals. For theoretical calculations of aggregates (or crystals) QM/MM approach (e.g., ONIOM model) will be adopted. Thus, the project aims at formal and conceptual development on the mechanism of AIE and AEE phenomena and the areas where the project outputs have potential applications are chemical industry, sensors and optoelectronics, bio-industry [e.g., in photodynamic therapy, (PDT, bio-imaging etc.)].