Fluorescence quenched and boosted by a-PET effect and host−guest complexation respectively in BODIPY-functionalized pillar[5]arene

Abstract

A BODIPY-functionalized ethoxypillar[5]arene (EtP5-BDP) and a guest compound G containing both of the cyano and triazole moieties were synthesized. The a-PET process between ethoxypillar[5]arene (EtP5) moiety and BODIPY moiety in EtP5-BDP was predicted by DFT/TDDFT calculations before experiment research. It was easier to occur for the a-PET process in polar solvents (e.g. acetone and CH3CN). The fluorescence of BODIPY moiety in EtP5-BDP was quenched to varying degrees in toluene, CHCl3, acetone and CH3CN. Due to the stronger interactions between EtP5 and G in toluene and CHCl3, when guest G was added, the fluorescence emissions of BODIPY moiety in EtP5-BDP in these two solvents were boosted but they still not recovered to the original emission level of BODIPY. Therefore, the electron transfer between EtP5 moiety and BODIPY moiety could be weakened but not inhibited completely by the host−guest complexation of EtP5-BDP and G. The ΔGCS was −0.01, −0.23, −0.40 and −0.42 eV for the PET process from EtP5 moiety to BODIPY moiety in toluene, CHCl3, acetone and CH3CN, respectively. The ECS of EtP5-BDP was lower than S1 energy state of BODIPY in various solvents. The charge transfer efficiencies (ΦCT) from EtP5 moiety to BODIPY moiety in toluene, CHCl3, acetone and CH3CN were 21%, 46%, 64% and 68%, respectively. All the results proved the a-PET process from EtP5 moiety to BODIPY moiety in EtP5-BDP.