Long-Lived Charge Transfer Excited States in HBC-Polypyridyl Complex Hybrids

Abstract

The synthesis of two bipyridine-hexa-peri-hexabenzocoronene (bpy-HBC) ligands functionalized with either (t)Bu or C12H25 and their Re(I) tricarbonyl chloride complexes are reported and their electronic properties investigated using spectroscopic and computational methods. The metal complexes show unusual properties, and we observed the formation of a long-lived excited state using time-resolved infrared spectroscopy. Depending on the solvent, this appears to be of the form Rebpy(•-)HBC(•+) or a bpy-centered π,π* state. TD-DFT calculations support the donor-acceptor charge transfer character of these systems, in which HBC is the donor and bpy is the acceptor. The ground state optical properties are dominated by the HBC chromophore with additional distinct transitions of the complexes, one associated with MLCT 450 nm (ε > 17 000 L mol(-1) cm(-1)) and another with a HBC/metal to bpy charge transfer, termed the MLLCT band (373 nm, ε = 66 000 L mol(-1) cm(-1)). These assignments are also supported by resonance Raman spectroscopy.

Chromophore-Functionalized Phenanthro-diimine Ligands and Their Re(I) Complexes

“…2025, 1922, and 1895 cm –1 , which correspond to fac -M(CO) 3 fragments lacking 3-fold symmetry. 43 , 68 The lower energy CO vibrations for 1-CN are somewhat shifted to higher frequencies (2024, 1926, and 1914 cm –1 ), which can be attributed to the substitution of the Cl – for the CN – ligand with a stronger π-accepting character.…”

“…An alternative possibility that cannot be ruled out on the basis of the available data involves electron transfer from the electron-rich chromophore to the photoexcited {Re II (diimine)} motif; such a process is not exceptional for rhenium(I) luminophores, and its probability depends on the properties of the diimine ligand. 43 , 108 The described photophysical behavior of 4 and 5 clearly contrasts with optical characteristics of the majority of rhenium(I) diimine compounds, which predominantly exhibit triplet emission or the formation of the intraligand dark triplet states. 32 − 36 …”

“… 44 In addition, a few complexes bearing pendant fluorophores exhibit singlet and triplet luminescence from two different spatially separated emissive centers. 39 , 43 , 96 …”

Carbon-rich “Click” 1,2,3-triazoles: hexaphenylbenzene and hexa-peri-hexabenzocoronene-based ligands for Suzuki–Miyaura catalysts

“…14 We have recently reported an HBC( t Bu) 5 -bpy (bpy = 2,2 0 -bipyridine) ligand and its corresponding Re(I) chlorotricarbonyl complex; this complex exhibits a long-lived charge transfer excited state. 11 Likewise, HPB ligands have been used to develop photophysically active metal complexes. 15 Despite the upsurge in interest in the development of HBC ligand systems, there are few general methods that enable the generation of soluble functionalised HBC architectures.…”

“…Penta(tert-butyl)-substituted hexaphenylbenzene (HPB)-and hexa-peri-hexabenzocoronene (HBC)-acetylenes were synthesised using established coupling conditions (ESI †). 11,13 Due to the limited solubility of these species in conventional polar solvents, an optimised synthesis of the triazoles was needed (ESI †). The triazoles 1a and 1b were optimally synthesised in dichloromethane using benzyl azide, [Cu(CH 3 X-ray quality crystals of both complexes were obtained by either a layered diffusion of methanol into a solution (2a) or the slow evaporation of a CH 2 Cl 2 solution (2b).…”