Uncovering photo-excited intramolecular charge transfer and ESIPT mechanism for 5,5′-(9,9-dioctyl-9H-fluorene-2,7-diyl) bis(2-benzo[d]thiazol-2-yl) phenol compound

In view of their facile synthetic routes and remarkable photo-induced stabilities, excited state intramolecular proton-transfer (ESIPT)-vibrant luminous materials have drawn more and more attention. In this work, we mainly focus on the photo-induced excitation behaviours, including excited state hydrogen bonding interactions and ESIPT reaction of a new 5,5 '-(9,9-dioctyl-9H-fluorene-2,7-diyl)-bis(2-benzo[d]thiazol-2-yl) phenol molecule theoretically. To be consistent with the previous experiment, we name this molecule as IIa. Using molecular electrostatic potential (MEP), we explored the dual intramolecular hydrogen bonding interactions in IIa form. Then on the level of chemical geometries and infrared (IR) spectra, we confirmed that the double hydrogen bonds should be enhanced upon photoexcitation. Probing into charge reorganisation, we found that hydrogen proton does prefer to be attracted by enhanced electronic densities around N3 and N6. Combining potential energy surfaces (PESs) and electronic spectra, the excited state intramolecular single proton-transfer (ESISPT) behaviour could be verified for IIa although it owns two hydrogen bonds.