Photophysics of Organometallic Platinum(II) Derivatives of the Diketopyrrolopyrrole Chromophore

Abstract

A pair of diketopyrrolopyrrole (DPP) chromophores that are end-functionalized with platinum containing "auxochromes" were subjected to electrochemical and photophysical study. The chromophores contain either platinum acetylide or ortho-metalated 2-thienylpyridinyl(platinum) end-groups (DPP-Pt(CC) and DPP-Pt(acac), respectively). The ground state redox potentials of the chromophores were determined by solution electrochemistry, and the HOMO and LUMO levels were estimated. The chromophores' photophysical properties were characterized by absorption, photoluminescence, and time-resolved absorption spectroscopy on time scales from sub-picoseconds to microseconds. Density functional theory (DFT) computations were performed to understand the molecular orbitals involved in both the singlet and triplet excited state photophysics. The results reveal that in both platinum DPP derivatives the organometallic auxochromes have a significant effect on the chromophores' photophysics. The most profound effect is a reduction in the fluorescence yields accompanied by enhanced triplet yields due to spin-orbit coupling induced by the metal centers. The effects are most pronounced in DPP-Pt(acac), indicating that the orthometalated platinum auxochrome is able to induce spin-orbital coupling to a greater extent compared to the platinum acetylide units.

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

“…69 On the other hand, a trans bis(trialkyl)phosphine Pt(II) bisacetylide complex with diketopyrrolopyrrole ligand has an ISC of 135 ps. 40 We also studied the possibility of the backward energy transfer from the coordinated ligand EB-1 to the EB-2 in complexes Pt-1 and Pt-4 by performing another pump probe experiment with 590 nm excitation for Pt-1 and Pt-4, at which the energy acceptor, i.e., the coordinated EB-2 ligand, was selectively excited. There is single bleach signal at 590 nm, which corresponds to the ground state bleaching of ligand EB- Pt-1 2.6 × 10 11 s −1 , 3.9 ps 1.92 × 10 10 s −1 (52.1 ps) Pt-2 9.89 × 10 9 s −1 (101.1 ps) Pt-3 4.23 × 10 10 s −1 (23.6 ps) Pt-4 6.9 × 10 10 s −1 , 14.5 ps 5.83 × 10 9 s −1 (171.5 ps)…”

“…39 However, complexes may show elusive photophysics, for example, short-lived intraligand triplet state ( 3 IL) was observed with PBI chromophore. 37,38,40 Recently, we prepared a series of visible light harvesting Pt(II) complexes with acetylide ligand based on coumarin 41 and Bodipy. 19,21,42,43 Generally these complexes show strong absorption of visible light (ε is up to 68 000 M −1 cm −1 in the range 500−600 nm), and the triplet state lifetime is as long as 128.4 μs.…”

Excitation Energy Transfer in meta‐Substituted Phenylacetylene Multibranched Chromophores

“…As shown in Figure , in addition to ground‐state bleaching (GSB) and stimulated emission (SE) in the spectral range λ =480–670 nm, a positive absorption band appears at λ ≈760 nm. The spectrum is presented about 300 fs after excitation, and then shows a relatively slow decay, which is due to depopulation of the relaxed excited state (S 1 state) of DPP . Evolution associated difference spectra (EADSs) were obtained with a sequential model for the exact description of the excited‐state relaxation dynamics of DPP.…”

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

“…The diketopyrrolopyrrole (DPP) chromophore has attracted much attention due to its strong absorption and high thermal stability. A Pt II complex with the diketopyrrolopyrrole chromophore was prepared (Figure ) . DPP‐containing Pt II complex 6 exhibits strong visible‐light absorption; the molar absorption coefficient is up to 110000 m –1 cm –1 at 633 nm.…”

“…The triplet excited state lifetime of the complex is 1.1 µs. The triplet excited state (T 1 state) of the complex is exclusively localized on the DPP moiety, indicated by the ground‐state bleaching band in the nanosecond transient absorption spectra …”