Photophysics of π-Conjugated Metal−Organic Oligomers:  Aryleneethynylenes that Contain the (bpy)Re(CO)₃Cl Chromophore

Abstract

A comprehensive study of a series of four monodisperse, metal-organic pi-conjugated oligomers of varying length is reported. The oligomers are based on the aryleneethynylene architecture, and they contain a 2,2'-bipyridine-5,5'-diyl (bpy) metal binding unit. The photophysical properties of the free oligomers and their complexes with the (L)Re(I)(CO)(3)X chromophore (where L = the bpy-oligomer and X = Cl or NCCH(3)) were explored by a variety of methods including electrochemistry, UV-visible absorption, variable temperature photoluminescence (PL), transient absorption (TA), and time-resolved electron paramagnetic spectroscopy (TREPR). The absorption of the free oligomers and the metal complexes is dominated by the pi,pi* transitions of the pi-conjugated oligomers. The free oligomers feature a strong blue fluorescence that is quenched entirely in the (L)Re(I)(CO)(3)X complexes. The metal-oligomers feature a weak, relatively long-lived red photoluminescence that is assigned to emission from both the (3)pi,pi* manifold of the pi-conjugated system and the dpi Re --> pi* bpy-oligomer metal-to-ligand charge transfer ((3)MLCT) state. On the basis of a detailed analysis of the PL, TA, and TREPR results an excited-state model is developed which indicates that the oligomer-based (3)pi,pi* state and the (3)MLCT states are in close energetic proximity. Consequently the photophysical properties reflect a composite of the properties of the two excited-state manifolds.

Photophysical Properties of Oligo­(phenylene ethynylene) Iridium(III) Complexes Functionalized with Metal‐Anchoring Groups

“…As for related ligands, we assign the lower-and higher-energy bands to long-and short-axis polarized π→π* transitions, respectively. [37,38,51] The absorption bands of Ir1-Ir4 are broader than those of the bare ligands 1-4 ( Figure 2 ) in the λ = 350-450 nm range. On the basis of previous reports, [28][29][30][31]33,37] we assign the first band to π→π* transitions centred on the ppy and phen ligands.…”

“…The redshift (up to 30 nm) of the bands into the λ = 360-390 nm range compared with those observed for 1-4 is in part attributed to the stabilization of the π-electron system of the phen chromophore as a result of the coordination to the cationic Ir III centre (see below). [51,52] [a] The concentrations were 3 × 10 -6 M. λ max = absorption maximum, ε = molar attenuation coefficient, λ em = emission maximum, E T = triplet energy, φ = fluorescence quantum yield, τ = luminescence lifetime, k r = radiative emission constant, and k nr = nonradiative emission constant. …”

Photophysics and Photochemistry of Stilbene-Containing Platinum Acetylides

“…[16][17][18] One area of particular interest in our work involves platinum acetylides. 19,20 This class of materials exhibits optical properties that are similar to oligo-and poly(phenylene ethynylene)s, 21 which can be thought of as the all-organic analogues of platinum acetylide oligomers and polymers.…”

Dibenzo[a, c]phenazine‐Based Donor‐Acceptor (D–A) Tetra Branched Molecules: Fine Tuning of Optical Properties

“…The decay data for compounds 4–7 could be fitted to a single exponential equation, and these compounds possessed similar and relatively long decay lifetimes (τF ∼8.7–16.7 ns; Table ). The observed lifetimes for 5–7 are known for π ‐conjugated planar molecules with strongly allowed long‐axis polarized π→π* singlet excited states, in contrast, compound 4 show much shorter lifetime (τF ∼0.67 ns) highlighted the presence of active intramolecular rotations of aryl rings in the excited state.…”