Introduction

This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book focuses on the excited-state intramolecular charge-transfer (ICT) in stable organic molecules as well as in inorganic complexes. It describes the origin and drawbacks of twisted ICT (TICT) state, planar ICT (PICT), rehybridized ICT (RICT) and wagging ICT (WICT) models. The book discusses the charge-transfer studies in some other molecules, including rhodamine derivatives, coumarin, oxazine, flavin and Nile red. It also discusses some of the methods to find the rate of electron-transfer process. The book describes the effect of the medium polarity and hydrogen bonding ability on the ICT process on some molecules. It summarizes some of the unresolved issues concerning the ICT processes. The book illustrates the applications of ICT probes in aggregation-induced emission (AIE), dye-sensitized solar cells, and organic-light-emitting diodes (OLEDs).