Excited State Properties and Energy Transfer within Dipyrrin‐Based Binuclear Iridium/Platinum Dyads: The Effect of ortho‐Methylation on the Spacer

Abstract

Luminescent cyclometalated iridium complexes based on pyridyl appended dipyrrin ligands were prepared and characterized both in the solid state and in solution. The functionalization of the peripheral pyridyl moiety causes dramatic changes on the emission properties of both mono- and hetero- binuclear complexes. A detailed photophysical investigation of the two mononuclear derivatives of the [(Ppy)(2)Ir(dpm-py)] family (Ppy=2-phenylpyridine, dpm-py=5-(4-pyridyl)dipyrrin) was carried out. Introduction of methyl groups at the 3 and 5 positions on the pyridyl unit diminishes the non-radiative rate constant by locking the peripheral pyridyl group orthogonally to the dipyrrinato plane. Thus, they limit the rotational degree of freedom, as well as the charge-transfer character of the excited state. The coordination of these two complexes to a cyclometalated [(dppy)Pt] fragment (dppy=2,6-diphenylpyridine) led to the formation of binuclear species in which the iridium and platinum complexes behave as acceptors and donors, respectively. In these heterobinuclear compounds, the methyl groups do not influence the energy transfer efficiency, which is estimated to be above 90 %. However, they do limit the charge-transfer character of the acceptor's excited state, as well as its rotational degree of freedom, thus avoiding the detrimental effect upon the photophysical performance.

Facile Synthesis of Luminescent Ir–Pt–Ir Trimetallic Complexes

“…where τ Ir‐Pt is the quenched donor (Ir units) lifetime within the trimetallic complex, and τ Ir is the unquenched lifetime of the model monometallic Ir complex 2 a . Equation (1) gives a value of k EnT =1.8×10 8 s −1 , which is a similar value to those of Dexter‐type energy transfer rates reported in other transition metal containing multimetallic systems, such as Pt, Ru and Ir . In addition, minimal spectral overlap between the emission spectrum of the [Ir(F 2 ppy) 2 ] + donor and the absorption spectrum of the [Pt(dbbpy)(C≡Cpy) 2 ] acceptor is observed.…”

“…In addition, such constructs can serve as models for understanding the long‐range excited‐state and charge transport processes found in natural photosynthesis . As such, a large number of photoactive multimetallic complexes have been prepared and studied …”

ANOMALOUS BEHAVIOR OF Ir(III) CYCLOMETALATED COMPLEXES: APPLICATION IN LIGHT-EMITTING ELECTROCHEMICAL CELLS

“…In addition, with the experimental data of Table 1 the radiative rate constant (k r ) and non-radiative rate constant (k nr ) were calculated. 24,25 Complex 1 shows a high value of k nr , which is consistent with the low QY and electrochemical gaps but, according to the energy gap law, is inconsistent with the higher energy of emission. 30,31,7 Consequently, it is possible to consider the possibility of a non-emitting state of lower energy, that the same time would be preventing the ISC.…”

“…k r = QY/τ and k nr = 1/τ-k r . 24,25 In Table 1 the electrochemical data are reported vs the Fc + /Fc couple and correspond to the oxidation process of Ir 3+/4+ , at positive potentials, and the reduction process of the ancillary ligand, at negative potential, as can be observed for another d 6 low spin complexes. 26 These values can be related with the energies of the highest-occupied molecular orbital (HOMO) and lowest-unoccupied molecular orbital (LUMO).…”

Zinc complexes incorporating with symmetrical and asymmetrical polydentate nitrogen-donor pyrrolyl ligands: Synthesis, characterization, and ring-opening polymerization

“…Pyrrole ligand systems have been widely applied as well as reviewed in porphyrin related chemistry [7e11]. Another raising researching field regarding pyrrole ligands is conjugated dipyrrin systems [12e14] which in combining with boron [15e18] and other elements [19,20] can be used as highly fluorescent material. In searching of zinc complexes containing pyrrole ligands, despite large amount of zinc porphyrin [21,22] and zinc dipyrrin complexes [23e25] have been studied, complexes containing mono-pyrrole (including linked mono-pyrrole) ligands [26e28] were less explored.…”