Efficient Complexation of Pyrrole‐Bridged Dizinc(II) Bisporphyrin with Fluorescent Probe Pyrene: Synthesis, Structure, and Photoinduced Singlet–Singlet Energy Transfer

Abstract

A diethylpyrrole-bridged dizinc(II) bisporphyrin (Zn(2)DEP) is reported that encapsulates fluorescent probe pyrene molecules through strong π-π interactions, which can relay information about the chemical environment in the interior of the host-guest supramolecular assembly. X-ray structures of both Zn(2)DEP and the encapsulated pyrene complex are reported, which provides a rare opportunity to investigate the structural changes upon guest binding. A comparative structural analysis demonstrated the exceptional ability of this bisporphyrin platform to open its binding pocket for pyrene encapsulation by a vertical displacement of more than 2.45 Å, although both Zn(2)DEP and the pyrene complex have nearly parallel porphyrin ring orientations. The (1)H NMR spectrum of the encapsulated pyrene complex in solution shows the upfield shifts of the pyrene protons due to a strong ring current effect, which demonstrates the retention of the solid-state structure in solution. To further assess the extent to which pyrene guests remain encapsulated in solution, a known fluorescence quencher, dimethylaniline, was added to the host-guest assembly, which shows no exciplex formation for days in nonpolar solvents. Thus, the assembly also retained the structural integrity in solution for a long time. The association constant (K(asso)) for such a complexation process in solution was observed to be 1.78×10(5) M(-2) for 1:2 binding. Steady-state fluorescence and lifetime studies indicate significant photoinduced singlet-singlet energy transformation from the excited state of pyrene to zinc bisporphyrin.

Study of Intermolecular Interactions in the Corrole Matrix by Solid‐State NMR under 100 kHz MAS and Theoretical Calculations

“…Most likely, the toluene molecule is encapsulated through p-p interactions in the host matrix [14] and the large upfield shifts result from a strong ring current effect that is due to the delocalized pelectrons on the corrole macrocycle. A similar HG system has been previously observed in a bis(porphyrin)-pyrene system, [15] in which the pyrene was sandwiched between porphyrin rings through p-p interactions and the pyrene protons were shifted to the upfield region by the ring current effect. Other corroles containing more electron-rich substituents may form similar aggregates, possibly with larger aromatic guests.…”

“…The indirectly detected 1 H{ 15 N} CP-HETCOR spectrum of 15 N-enriched 1 is shown in Figure 1 B, with the assignments based on the theoretically predicted 15 N chemical shifts (À233, À147, À264, and À259 ppm for N A , N B , N C , and N D , respectively, see Scheme 1 and Supporting Information for details). The well resolved 1 H-15 N cross-peaks demonstrate that no exchange among H N protons (tautomerization) occurs in this system, at least at rates exceeding 1 kHz.…”

Efficient Host‐Guest Complexation of a Bisporphyrin Host with Electron Deficient Guests: Synthesis, Structure, and Photoinduced Electron Transfer

“…The isotopic distribution patterns of the experimental and theoretical mass are exactly matching for these complexes. X‐ray structures of H 4 DEP and Zn 2 DEP were reported earlier9c,d by us; however, all the host‐guest complexes (H 4 DEP⋅NAN, H 4 DEP⋅9‐DCF, Zn 2 DEP⋅ANQ, and Zn 2 DEP⋅NBD‐Cl) reported here are new and also enable us to have direct comparison upon guest binding. Detailed synthetic procedures and their spectral characterizations are given in the experimental section.…”

“…Free‐base diethylpyrrole‐bridged bisporphyrin (H 4 DEP) and its dizinc(II) derivative (Zn 2 DEP) were synthesized following procedures reported earlier 9c,d. Upon addition of excess guest (NAN/9‐DCF/ANQ/NBD‐Cl) to a chloroform solution of host (H 4 DEP/Zn 2 DEP), the subsequent solvent diffusion by acetonitrile in air at room temperature yielded dark‐colored crystalline solids, due to the formation of respective host‐guest sandwich complexes, H 4 DEP⋅NAN, H 4 DEP⋅9‐DCF, Zn 2 DEP⋅ANQ, and Zn 2 DEP⋅NBD‐Cl.…”

“…Recently, Shionoya and coworkers have reported host‐guest intercalation between porphyrin dimers and various aromatic molecules. [17] Previously, our group has also reported such efficient host‐guest complexation, where guests like pyrene, TCNQ, acridinium ion, and TNF were encapsulated in a bisporphyrin host 9a,c,d. However, crystallographic evidence of such host‐guest interactions are still scarce and detailed understanding of the solid and solution phase interactions would offer substantial insight towards rational control over guest selectivity and properties therein.…”