Quantitative Design of Bright Fluorophores and AIEgens by the Accurate Prediction of Twisted Intramolecular Charge Transfer (TICT)

Abstract

Inhibition of TICT can significantly increase the brightness of fluorescent materials. Accurate prediction of TICT is thus critical for the quantitative design of high‐performance fluorophores and AIEgens. Herein, we computationally modeled TICT of 14 types of popular organic fluorophores with time‐dependent density functional theory (TD‐DFT). Based on a comprehensive comparison of various representative exchange‐correlation functionals and solvent formalisms, we established a reliable and generalizable computational approach for modeling TICT formations. To validate our approach, we revisit and conclude a two‐decade‐long mechanistic debate on the TICT formation in 6‐propionyl‐2‐(dimethylamino)naphthalene (PRODAN) with unambiguous experimental proofs, and quantitatively design PRODAN derivatives with doubled brightness, enhanced photostability and excellent bioimaging utilities by inhibiting TICT formations. To further demonstrate the prediction power of our approach, we quantitatively designed a boron dipyrromethene (BODIPY)‐based AIEgen which exhibits (almost) barrierless TICT rotations in monomers. Subsequent experiments validated our molecular design and showed that the aggregation of this compound turns on bright emissions with ~27 times of fluorescence enhancement, as TICT formation is inhibited in molecular aggregates. We believe that our approach will significantly aid the development of TICT‐based functional materials and facilitate the evolution of dye chemistry from trial‐and‐error to design‐based molecular engineering.