Size dependent hydrogen-bonded methanol wires regulating the fluorescence On-Off of 1-H-pyrrolo[3,2-h]quinoline•(MeOH)n=1,2 complexes with ESMPT

Studies of excited state multiple proton transfer (ESMPT) are paramount importance for both biological systems and chemical reactions while its mechanism in a controllable manner has been long sought. For this purpose, we conducted a theoretical study on the ESMPT mechanisms of 1-H-pyirolo[3,2-h]guinoline (PQ) connecting different number methanol (MeOH) molecules ( PQ-(MeOH)(n=)(1,2)). The results show that the ESMPT process can occur for PQ-(MeOH)(n=1,2) complexes and Me0H molecules can effectively regulate the proton transfer barriers. The non-fluorescence of PQ-MeOH was explained by the combination of rapid ESMPT and following intersystem crossing (ISC) processes. The observed fluorescence of PQ-(MeOH)(2) was owing to the contribution of increased excited-state barriers to emission is greater than the consumption of ISC process. These exciting findings revealed the cooperation mechanism between ESMPT and ISC processes for PQ-(MeOH), whereas the competitive mechanism for PQ-(MeOH)(2). Our work firstly implemented the bidirectional regulation of the ESMPT mechanism, which will open new avenues for improving the luminescence properties and characterizing the cluster structure. (C) 2020 Elsevier B.V. All rights reserved.