Tuning the Dipolar Second‐Order Nonlinear Optical Properties of Cyclometalated Platinum(II) Complexes with Tridentate N^C^N Binding Ligands

Abstract

Appropriate functionalization of the cyclometalated ligand, L, and the choice of the ancillary ligand, X, allows the dipolar second-order nonlinear optical response of luminescent [PtLX] complexes--in which L is an N^C^N-coordinated 1,3-di(2-pyridyl)benzene ligand and X is a monodentate halide or acetylide ligand--to be controlled. The complementary use of electric-field-induced second-harmonic (EFISH) generation and harmonic light scattering (HLS) measurements demonstrates how the quadratic hyperpolarizability of this appealing family of multifunctional chromophores, characterized by a good transparency throughout much of the visible region, is dominated by an octupolar contribution.

Tuning the dipolar second-order nonlinear optical properties of 5-π-delocalized-donor-1,3-di(2-pyridyl)benzenes, related cyclometallated platinum(ii) complexes and methylated salts

“…23--24 In particular, the methyl derivative Pt(Medpyb)Cl is characterized by a good µβ EFISH value (--480 x 10 -48 esu), as evidenced by the EFISH technique, working in DMF solution with an incident radiation wavelength of 1.907 µm, due to a high dipole moment (10.2 D) and a good β EFISH value (--47 x 10 -30 esu). 28 The negative sign of the quadratic hyperpolarizability of this complex is in agreement with a decrease of the excited state dipole moment with respect to the ground state, 52 suggesting that the second--order dipolar NLO response is dominated by the charge transfer from platinum to the cyclometallated ligand. 28 The HOMO/LUMO plots reported in Figure 1 for 1Pt--3Pt are consistent with this picture: the HOMO of the metal complexes all show a Pt d yz contribution and a charge delocalization on the central substituted phenyl systems, while the LUMO and LUMO+1 show an involvement of the cyclometallating pyridyl units.…”

“…28 The negative sign of the quadratic hyperpolarizability of this complex is in agreement with a decrease of the excited state dipole moment with respect to the ground state, 52 suggesting that the second--order dipolar NLO response is dominated by the charge transfer from platinum to the cyclometallated ligand. 28 The HOMO/LUMO plots reported in Figure 1 for 1Pt--3Pt are consistent with this picture: the HOMO of the metal complexes all show a Pt d yz contribution and a charge delocalization on the central substituted phenyl systems, while the LUMO and LUMO+1 show an involvement of the cyclometallating pyridyl units. As shown in Table 1, substitution of the methyl group Pt(Medpyb)Cl (Chart 1) by a π--delocalized vinyl donor group, in position 5 of the phenyl ring of the cyclometallated 1,3--di(2--pyridyl)benzene moiety, causes a significant enhancement of the absolute value of µβ EFISH (factor of 1.8, 1.7 and 2.6 for 1Pt, 2Pt and 3Pt, respectively).…”

“…27 The good second--order nonlinear optical properties of Pt(Medpyb)Cl (MedpybH = 5--methyl--1,3--di(2--pyridyl)benzene; Chart 1) have also been evidenced by the electric--field induced second harmonic generation (EFISH) technique. 28 However, the effect of a π--delocalized electron--donating substituent on the cyclometallated 1,3--di(2--pyridyl)benzene ligand of such Pt(II) complexes has not been investigated from an NLO point of view. Such an investigation is appealing, because the absorption bands of this kind of complex are red shifted by increasing the donor ability of the substituent at the central 5--position of the cyclometallating ring, through stabilisation of charge transfer states, 29,30 and it is known that the presence of charge--transfer transitions at low energy can lead to a high quadratic hyperpolarizability.…”

Neutral N^C^N terdentate luminescent Pt(ii) complexes: their synthesis, photophysical properties, and bio-imaging applications

“…[6][7][8][9][10] Cyclometallated derivatives are usefully employed for the preparation of triplet emitters for highly efficient OLED (organic light emitting diode) devices 7,[11][12][13][14] and for their appealing second-order nonlinear optical (NLO) properties. [15][16][17][18] Another fast emerging field regarding luminescent Pt(II) complexes is their application as luminescent labels for bioimaging. [19][20][21][22][23] Although fluorescent organic labels are still the leading choice for such applications, [24][25][26] phosphorescent Pt(II) complexes are slowly gaining attention and could outclass organic molecules.…”

Attachment of Luminescent Neutral “Pt(pq)(C≡CtBu)” Units to Di and Tri N-Donor Connecting Ligands: Solution Behavior and Photophysical Properties

“…The interest of alkynyl platinum(II) complexes stems from their rich structural diversity [1][2][3][4], their interesting chemical reactivity [1] and more recently from their increasing potential in material science [5][6][7][8][9][10][11][12][13][14][15][16][17]. In this field, light-emitting complexes have attracted a great deal of attention owing to their use in optoelectronic devices, chemosensors, photovoltaic cells and photocatalysis.…”