Intramolecular charge transfer for optical applications

摘要

Tuning of intramolecular charge transfer (ICT) in a molecule could be used to modulate its linear and nonlinear optical (NLO) response properties. Over the years, the ICT process in the so-called "push-pull " molecules in which electron donor (D) and acceptor (A) groups are connected either directly or through a pi-electron bridge has been used for emission color tuning, modulating absorption maxima, optimizing first or higher order hyperpolarizabilities, and two-photon absorption (TPA), among others. As ICT is the functional basis of many optoelectronic and semiconductor devices, optimizing the parameters involved in this process as well as modeling the effect of the environment and intermolecular interaction are crucial for these applications. NLO processes such as second harmonic generation, sum-frequency generation, and TPA have been used extensively for numerous technological applications, such as optical switching, optical limiting, bioimaging, and biophotonics. Recently, through-bond and through-space ICT have been employed to tune the reverse intersystem crossing that facilitates thermally activated delayed fluorescence for fabricating next-generation organic light-emitting diodes. Aggregation-induced emission of ICT molecules either alone or in combination with the other phenomenon, such as TPA, could be useful in many optical applications. In this perspective, the state-of-the-art and challenges in designing ICT-based molecules and materials for optical applications will be discussed. The underlying theories used to quantify the magnitude of ICT and NLO response are mentioned, followed by a discussion on the latest development and scope of using these molecules and materials for optical applications.