Effectively regulation of the ESIPT process via ring-annelation modification for schiff base derivatives: A theoretical study

Precise regulation of the excited state intramolecular proton transfer (ESIPT) process using different new approaches remains a challenging task. Herein, based on an experimentally synthesized novel Schiff base (sp) which can be used as a Cr3+ ion sensor, the ESIPT mechanism and photophysical properties of six different Schiff base derivatives (b, 1n, 2n, 1a, 2a and sp) are theoretically analyzed by using the molecular ring-annelation modification to study the mechanism of their regulation for the ESIPT process. We find that the difference of the aromatic substituent at the hydrogen bond acceptor terminals will regularly enhance the excited-state intramolecular hydrogen bonds (IHBs) and weaken the intramolecular charge transfer (ICT) process. That is, the ring-annelation modification results in the expansive irradiative channels and restricted ICT process for Schiff base derivatives, thereby effectively reducing molecular ESIPT barrier. The above conclusions are confirmed by the qualitative and quantitative analyses of related hydrogen bonds and electron-hole. Our work provides a robust strategy for creating high-performance fluorescent chromophores via ESIPT manipulation.