Broad-Band N^∧N Pt(II) Bisacetylide Visible Light Harvesting Complex with Heteroleptic Bodipy Acetylide Ligands

Abstract

Pt(II) dbbpy bisacetylide (dbbpy = 4,4'-di(tert-butyl)-2,2'-bipyridine) complex (Pt-1) with two different Bodipy ligands was prepared with the goal to attain broad-band visible light absorbing, efficient funneling of the photoexcitation energy (via resonance energy transfer, RET) to the energy acceptor and high triplet formation quantum yields. Construction of the above-mentioned molecular structural motif is challenging because two different arylacetylide ligands are incorporated in the complex; normally two homoleptic acetylide ligands were used for this kind of N(∧)N Pt(II) complexes. A reference complex with trans bis(tributylphosphine) Pt(II) bisacetylide protocol (Pt-4) was prepared for comparison of the photophysical properties. The two different Bodipy ligands in Pt-1 and Pt-4 constitute singlet/triplet energy donor/acceptor, as a result the harvested photoexcitation energy can be funneled to the triplet state confined on one of the two Bodipy ligands. The photophysical properties of the complexes were studied with steady state UV-vis absorption and luminescence spectroscopies, femto- and nanosecond transient absorption spectroscopies, cyclic voltammetry, as well as DFT/TDDFT calculations. Fluorescence/phosphorescence dual emission were observed for the complex. The ultrafast intramolecular singlet/triplet energy transfer in Pt-1 was confirmed by the transient absorption spectroscopy (kFRET = 2.6 × 10(11) s(-1), ΦFRET = 87.1%) followed by an intersystem crossing (kISC = 1.9 × 10(10) s(-1)), and the triplet state lifetime (τT) is 54.1 μs. The reference complex Pt-4 shows drastically different kinetics with kFRET = 6.9 × 10(10) s(-1), ΦFRET = 81.0%, kISC = 5.83 × 10(9) s(-1), and τT = 147.9 μs. Different singlet oxygen ((1)O2) quantum yields (ΦΔ = 75% and 70%) and triplet state quantum yields (ΦT = 91% and 69%, respectively) were observed for complexes Pt-1 and Pt-4.

Near-IR Broadband-Absorbing trans-Bisphosphine Pt(II) Bisacetylide Complexes: Preparation and Study of the Photophysics

“…53−55 Recently we prepared N^N Pt(II) bisacetylide complex with heteroleptic acetylide ligands. 56 But two different acetylide ligands are unable to be introduced in a stepwise way. Previously unmodified Bodipy ligands were used for preparation of the Pt(II) complexes, but the absorption wavelength is shorter than 600 nm.…”

“…70 Recently we prepared N^N Pt(II) bisacetylide complex with heteroleptic acetylide ligands. 56 The singlet-energy transfer rate constant is 10-fold faster, 2.6 × 10 11 s −1 .…”

“…A recently reported broadband visible-lightabsorbing N^N Pt(II) bisacetylide complex with heteroleptic acetylide ligands shows longer triplet-state lifetime of 68.21 μs. 56 The triplet state of the ligand L−1 was produced with the sensitization method; that is, 2,6-diiodoBodipy (B−2, Scheme 1) was used as the triplet-state energy donor (photosensitizer) and L−1 as the triplet-state energy acceptor (Figure 10). 87 The triplet-state lifetime of B−2 was reduced to 22.8 μs in the presence of L−1.…”

Photophysical Properties of Visible‐Light‐Harvesting PtII Bis(acetylide) Complexes

“…N ^ N Pt II bis(acetylide) complex 32 and bis(phosphine)Pt II bis(acetylide) complex 33 with heteroleptic acetylide ligands were prepared by our group (Figure ) . The structural motif of complex 32 is unusual, because normally two identical acetylide ligands are attached to the Pt II atom in an N ^ N Pt II bis(acetylide) complex.…”

“…UV/Vis absorption spectra of complexes 32 and 33 and of Bodipy ligands 2‐BDP and 8‐BDP . Reprinted from the literature, with permission . Copyright 2015, American Chemical Society.…”