A Theoretical Investigation of Substituent Effects on the Absorption and Emission Properties of a Series of Terpyridylplatinum(II) Acetylide Complexes

Abstract

A comprehensive calculational investigation has been carried out on a series of complexes of the type [(terpyridyl‐R1)Pt(C≡C‐R2)], where terpyridyl‐R1 is a series of substituted 2,2':6',2''‐terpyridyl ligands and C≡C‐R2 is a series of substituted acetylide ligands. In one series of complexes (I), the energy of the electronic excited state is varied by changing the substituents on the terpyridyl ligand (R1). In a second series of complexes (II), this electronic structure variation is obtained by changing the para substituents (R2) of the acetylide ligand. The effect of varying the substituents on the lowest‐energy excited states of the complexes has been assessed by calculating their electronic structures and excitation energies. We anticipated that introduction of electron‐withdrawing substituents on the terpyridyl ligand will benefit the LLCT (or MLCT) and prohibit the nonradiative pathways via d‐d transitions in these complexes; introduction of electron‐donating substituents on the acetylide ligand can also prohibit the nonradiative pathways by increasing the energy gaps between the HOMO–LUMO and d‐d transitions. The results also reveal that the lowest‐energy excitations of all complexes of series I and IIa–b complexes are dominated by a π(C≡C) → π*(terp) (LLCT) transition mixed with some energetically dπ(Pt) → terpyridyl (MLCT) transition. However, for the complexes IIc–IId, in which phenyl rings are introduced on the acetylide ligand, the lowest‐lying absorptions of IIc and IId are predominately LLCT in character, with less MLCT mixture, due to a lower contribution of the Pt(d) orbital to the HOMO, while for IIe, with a stronger donor on the acetylide, the lowest‐lying absorption is completely LLCT in character. The absorption and emission calculations using the TDDFT method are based on the optimized geometries obtained at the B3LYP/LanL2DZ and CIS/LanL2DZ levels, respectively. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Spectroscopic Properties of Orthometalated Platinum(II) Bipyridine Complexes Containing Various Ethynylaryl Groups

“…As a result, the energy gap between the MLCT and d–d states increases favorably 10. Theoretical investigations confirm that substituents on the ancillary ligand can play a major role in tailoring the optical properties of such complexes 10c. This trend was confirmed in many platinum(II) σ‐alkynyl complexes displaying high quantum yield and long‐lived photoluminescence from MLCT excited states 11.…”

“…One is that the CT absorption extends to significantly longer wavelengths for all complexes in series II and III . According to theoretical work on related systems,10c, 12a, 41, 42 the extra excitation at the longer wavelength end of the spectrum has ligand‐to‐ligand charge transfer (LLCT) character. Interligand CT excitation is possible when an orbital of the coligand, in this case an electron‐rich ethynylaryl group, mixes into the HOMO.…”

Synthesis, structures and properties of a new series of platinum–diimine–dithiolate complexes

“…Due to the size of the complexes (up to 76 atoms, no symmetry), loose geometry optimisation criteria were used. Molecular orbital compositions were calculated as described by Liu et al 37…”

Electronic structures and optical properties of neutral substituted fluorene-based cyclometalated platinum(II)–acetylide complexes: A DFT exploration

“…Therefore, the nonlinear optical (NLO) response for this kind of materials is interesting and an important topic, though the donor group is generally acted by transition-metal segments. Nowadays, theoretical chemical calculations have been proved to be useful for gaining insight into the optoelectronic properties of transition-metallic complexes [66][67][68][69][70][71]. Hence, in this work, we study the mechanism of charge transfer, the more particular description of linear and nonlinear optical properties for several mono-and dinuclear tridentate cyclometalated platinum(II) r-acetylide complexes bearing fluorene substituents (Chart 1),…”