A 3.0 μs Room Temperature Excited State Lifetime of a Bistridentate Ru^II−Polypyridine Complex for Rod-like Molecular Arrays

Abstract

A bistridentate RuII-polypyridine complex [Ru(bqp)2]2+ (bqp = 2,6-bis(8'-quinolinyl)pyridine) has been prepared, which has a coordination geometry much closer to a perfect octahedron than the typical Ru(terpyridine)2-type complex. Thus, the complex displays a 3.0 mus lifetime of the lowest excited metal-to-ligand charge transfer (3MLCT) state at room temperature. This is, to the best of our knowledge, the longest MLCT state lifetime reported for a RuII-polypyridyl complex at room temperature. The structure allows for the future construction of rod-like, isomer-free molecular arrays by substitution of donor and acceptor moieties on the central pyridine units. This makes it a promising photosensitizer for applications in molecular devices for artificial photosynthesis and molecular electronics.

Vectorial Electron Transfer in Donor–Photosensitizer–Acceptor Triads Based on Novel Bis‐tridentate Ruthenium Polypyridyl Complexes

“…Schematic energy diagram of relevant excited and charge-separated states versus the ground state (GS) for the triads 1 a and 3 a. Triplet excited-state energies are taken from the literature. [23,35] The charge-separated-state energies are calculated from data in Table 1, as described in the text. Solid arrows mark the observed charge-separation (CS) and charge-recombination (CR) processes.…”

“…[21] As an alternative approach the trans-[RuA C H T U N G T R E N N U N G (bpy) 2 (py) 2 ] 2 + (py = pyridine) motif has been used, but it unfortunately also suffers from a short room-temperature excited-state lifetime and, additionally, poor photostability. [22] Recently, our group has detailed the rational development [23,24] and facile synthesis [25,26] of a new class of Ru II bistridentate photosensitizers, based on Ru II bis-2,6-di(quinolin-8-yl)pyridine ([RuA C H T U N G T R E N N U N G (dqp) 2 ] 2 + ). An almost perfect octahedral coordination sphere, with short and equal Ru-N dis-A C H T U N G T R E N N U N G tances, and consequently a strong ligand field is created through the use of six-membered chelates leading to photophysical properties similar to those of [RuA C H T U N G T R E N N U N G (bpy) 3 ] 2 + .…”

“…2 + , [23] the broad band at 495 nm can be assigned to the lowest excited singlet MLCT state, and the higher bands (at 290 and 340 nm) are attributed to ligand-centred (LC) transitions. The small peak at 410 nm in the absorption spectrum of 1 a is found in all phenyl-linked complexes studied here (1 a, 1 b, 2 a and 2 b).…”

“…2.35 eV according to the literature. [35] Thus, energy transfer from the 3 MLCT excited state (E 00 = 1.84 eV for [RuA C H T U N G T R E N N U N G (dqp) 2 ] 2 + in a MeOH/EtOH glass) [23] to form the quinone triplet is a considerably uphill process, and not a likely quenching mechanism. From the electrochemistry data given in Table 1, the driving force for the electron transfer is approximately DG [ 45] In principle, the PTZ + Ru II Q À charge-separated state could be formed through two alternative routes, reductive quenching [Eq.…”

Resolution of Conformationally Chiral mer‐[Ru(dqp)2]2+ and Crystallographic Analysis of [δ,δ‐Ru(dqp)2][Δ‐TRISPHAT]2 (dqp=2,6‐Di(quinolin‐8‐yl)pyridine; TRISPHAT=Tris(tetrachlorocatecholate)phosphate)

“…[7][8][9][10] As a consequence of all six-membered chelates, the dqp ligands adopt nonplanar helical conformations. The conformation of one ligand predetermines the conformation of the second ligand (either l,l or d,d enantiomers) leading to intramolecular p-stacking between quinoline pairs.…”