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.

Intersystem crossing in π-conjugated donor–acceptor–donor chromophores is controlled by the strength of the donor–acceptor interaction.

A series of trans-N-heterocyclic carbene (NHC) platinum(ii) acetylide complexes of the form (ICy)2Pt(R)2 (where ICy = 1,3-bis-(cyclohexyl)imidazol-2-ylidene and R = 1-Ethynyl-4-(phenylethynyl)benzene (PE2), 2-(9,9-Diethyl-9H-fluoren-7-yl)benzo[d]thiazole (BTF), and 9,9-Diethyl-7-ethynyl-N,N-diphenyl-9H-fluoren-2-amine (DPAF), respectively), were synthesized via Hagihara reaction of the unprotected aryl-acetylide ligands with trans-(ICy)2PtCl2 () in 47-73% yield. Precursor was generated in a one-pot synthesis via formation of a silver carbene precursor followed by transmetallation, and was obtained in high yield (95%). The single-crystal X-ray structures of , were determined and analyzed. The photophysical properties of were compared to their respective tributyl phosphine (PBu3) analogues. The optical properties of the series were studied by UV-Vis spectroscopy, photoluminescence spectroscopy, nanosecond transient absorption spectroscopy, and open aperture nanosecond z-scan. Coupling of the organic chromophores to the platinum center affords efficient intersystem crossing as concluded by the complexes' low fluorescence quantum yields, efficient phosphorescence and intense T1 - Tn absorption. Open aperture z-scan with 606 nm, 10 ns laser pulses showed comparable optical attenuation relative to a standard sample of (PBu3)2Pt(DPAF)2 (). Pulse limiting was achieved via a dual-mechanism of two-photon absorption (2PA) coupled with excited-state absorption (ESA). TD-DFT Computations were also employed for to give greater insight into the nature of the singlet-singlet electronic transitions.