A Porphyrin-Based Molecular Tweezer: Guest-Induced Switching of Forward and Backward Photoinduced Energy Transfer

Abstract

A bisindole-bridged-porphyrin tweezer (1), a pair of zinc porphyrins (PZn's) connected to bisindole bridge (BB) via the Cu(I)-mediated alkyne-azide click chemistry, exhibited unique switching in forward and backward photoinduced energy transfer by specific guest bindings. The addition of Cu(2+) caused a change in electronic absorption and fluorescence quenching of 1. MALDI-TOF-MS and FT-IR analyses indicated the formation of stable coordination complex between 1 and Cu(2+) (1-Cu(II)). Without Cu(2+) coordination, the excitation energy flows from BB to PZn's with significantly high energy transfer efficiency. In contrast, the direction of energy flow in 1 was completely reversed by the coordination of Cu(2+). The difference in fluorescence quantum yield between 1 and 1-Cu(II) indicates that more than 95% of excitation energy of PZn flows into Cu(II)-coordinated BB. The energy transfer efficiency was further controlled by bidentate ligand coordination onto 1-Cu(II). When pyrophosphate ion was added to 1-Cu(II), the recovery of fluorescence emission from PZn was observed. The quantum mechanical calculations indicated that the Cu(II)-coordinated BB has square planar geometry, which can be distorted to form octahedral geometry due to the coordination of bidentate ligands.

Plasmon‐Enhanced Fluorescence‐Based Core–Shell Gold Nanorods as a Near‐IR Fluorescent Turn‐On Sensor for the Highly Sensitive Detection of Pyrophosphate in Aqueous Solution

“…The quenching effect should be related to Cu 2+ binding with the carboxyl groups on the surface of AuNR@SiO 2 @TCPP, and formation of AuNRs@SiO 2 @TCPP‐Cu 2+ complexes. Owing to the stronger coordination of PPi with Cu 2+ than carboxyl group, when PPi was added, the fluorescence intensity of the system could be recovered partially, and effectively withdraw the Cu 2+ from the complexes of AuNR@SiO 2 @TCPP‐Cu 2+ . In fact, using strong affinity between PPi and Cu 2+ complexes for detecting PPi was explicitly described in the previous reports .…”

“…Cu 2+ is a well‐known highly efficient fluorescent quencher due to its paramagnetic properties via electron or energy transfer, and as a result the copper porphyrin (TCPP‐Cu 2+ ) has a weak fluorescence . Upon the introduction of PPi, the strong affinity between Cu 2+ and PPi can promote the disassembly of the turn‐off state of TCPP‐Cu 2+ complexes, and the process can be observed by monitoring the fluorescence recovery of TCPP (Scheme B). In addition, no obvious change in fluorescence intensity would be expected for other interferences from analogues of PPi as well as others, because the formed complex of Cu 2+ and PPi through coordination could be more stable than others .…”

Stimuli-Responsive Metal–Ligand Assemblies

“…77 representation of guest induced switching of excitation energy transfer. 79 Reprinted with permission from ref 79 . Copyright 2014 American Chemical Society.…”

Elucidating the Ultrafast Dynamics of Photoinduced Charge Separation in Metalloporphyrin-Fullerene Dyads Across the Electromagnetic Spectrum

“…[14][15][16][17][18][19] When containing a central metal ion with unpaired d electrons, such as Cu II , MPs have been associated with the occurrence of energy and charge migration mediated by enhanced electromagnetic coupling. [20][21][22][23][24][25][26] Although this specific interaction presents definite potential, its practical utilization in photodriven molecular devices remains largely under-developed. This can be traced back to the fact that the photoinduced dynamics are complicated by the participation of (d,), (,d) or (d,d) charge-transfer (CT) states that have been postulated at the origin of the prompt deactivation undergone by the photoactive state.…”