Dinuclear Rhenium Complexes with a Bridging Helicene-bis-bipyridine Ligand: Synthesis, Structure, and Photophysical and Chiroptical Properties.

Nidal Saleh,Nicolas Vanthuyne,Gilles Muller,Jeanne Crassous,Jochen Autschbach,Katarzyna Matczyszyn,Joanna Olesiak‐Banska,Victoria Y Chang,Monika Srebro‐Hooper,J A Gareth Williams,Anna Pniakowska,Debsouri Kundu

doi:10.1002/cplu.202000559

Abstract

By attaching pyridine groups to a diaza[6]helicene, a helical, bis-ditopic, bis-N N-coordinating ligand can be accessed. Dinuclear rhenium complexes featuring this bridging ligand, of the form [{Re(CO)3 Cl}2 (N N-N N)], have been prepared and resolved to give enantiopure complexes. These complexes are phosphorescent in solution at room temperature under one- and two-photon excitation. Their experimental chiroptical properties (optical rotation, electronic circular dichroism and circularly polarized emission) have been measured. They show, for instance, emission dissymmetry factors of c.a. ±3x10-3 . Quantum-chemical calculations indicate the importance of stereochemistry on the optical activity, pointing towards further design improvements in such types of complexes.

Highlights

N^N-Bidentate ligands incorporating 2,2'-bipyridine units are widely used in coordination chemistry and provide a great variety of transition-metal complexes.[1]
The two appended 2pyridyl groups are almost coplanar with the helicenic core and the nitrogen atoms within each 2,2’-bipy unit are mutually trans to one another
The analysis revealed that the main positive intensity observed in the electronic circular dichroism (ECD) spectra of Re-1 originates from excitations no. 5, 6, and 7 calculated at between 345 and 330 nm

Summary

Introduction

N^N-Bidentate ligands incorporating 2,2'-bipyridine (bipy) units are widely used in coordination chemistry and provide a great variety of transition-metal complexes.[1]. Calculated (using TDDFT-BHLYP/SV(P) with a continuum solvent model for CH2Cl2) luminescence energies for the ligand 3 and the Re(I) complexes Re-1 and Re-2 agree well with the experimental emission data measured at low temperature (see Table S2.4 In particular, the computations correctly reproduce spectral positions of the fluorescence (3) and phosphorescence (3, Re-1,2) maxima with the similar values of T1→S0 transition energiesobtained for Re-1 and Re-2 and their moderate red-shift compared to the phosphorescence of 3.

Results

Conclusion