Tuning excited-state charge/proton transfer coupled reaction via the dipolar functionality

Based on design and synthesis of I, II, and III, we demonstrate an ingenious approach to fine-tuning the excited-state intramolecular charge transfer (ESICT) coupled excited-state intramolecular proton transfer (ESIPT) reaction via the dipolar functionality of the molecular framework. Both I and 11 exhibit remarkable dual emission due to the different solvent-polarity environment between ESICT and ESIPT states, while the interplay of two charge-transfer entities in III leads to ESIPT decoupling from the solvent-polarity effect, resulting in a unique proton-transfer tautomer emission. The results make further rational design of the ESICT/ ESIPT coupled systems feasible simply by tuning the net dipolar effect. Accordingly, systematic investigation of the correlation in regards to the difference in dipolar vectors between ESICT and ESIPT versus solvent-polarity induced barriers becomes possible.