Pyrene fluorescence in 2,7-di(4-phenylethynyl)pyrene-bridged bis(alkenylruthenium) complexes.

Complexes PyrDPE-RuCl and PyrDPE-Ruacac with a π-extended 2,7-di(4-phenylethynyl)pyrene linker undergo simultaneous one-electron oxidations of their {Ru}-styryl entities. The absence of an intervalence charge-transfer (IVCT) band at intermediate stages, where the mixed-valent, singly oxidized radical cation is present, and spin density confinement to the terminal styryl ruthenium site(s) are tokens of a lack of electronic coupling between the {Ru} entities across the π-conjugated linker. The close similarity of the linker-based π → π* bands in the complexes and the free ligand and their insensitivity towards oxidations at the terminal sites indicate that the central pyrenyl fluorophore is electronically decoupled from the electron-rich {Ru}-styryl termini. As a consequence, the complexes offer stable pyrene-based fluorescence emissions at 77 K, which are red-shifted from that of the linker.

A Dibenzotetrathiafulvalene-Bridged Bis(alkenylruthenium) Complex and Its One- and Two-Electron-Oxidized Forms.

We report on the synthesis of the new bis(alkenylruthenium) complex DBTTF-(ViRu)2 with a longitudinally extended, π-conjugated dibenzotetrathiafulvalene (DBTTF) bridge, characterized by multinuclear NMR, IR, and UV/vis spectroscopy, mass spectrometry, and single-crystal X-ray diffraction. Cyclic and square-wave voltammetry revealed that DBTTF-(ViRu)2 undergoes four consecutive oxidations. IR, UV/vis/near-IR, and electron paramagnetic resonance spectroscopy indicate that the first oxidation involves the redox-noninnocent DBTTF bridge, while the second oxidation is biased toward one of the peripheral styrylruthenium entities, thereby generating an electronically coupled mixed-valent state ({Ru}-CH═CH)•+-DBTTF•+-(CH═CH-{Ru}) [{Ru} = Ru(CO)Cl(PiPr3)2]. The latter is apparently in resonance with the ({Ru}-CH═CH)•+-DBTTF-(CH═CH-{Ru})•+ and ({Ru}-CH═CH)-DBTTF2+-(CH═CH-{Ru}) forms, which are calculated to lie within 19 kJ/mol. Higher oxidized forms proved too unstable for further characterization. The reaction of DBTTF-(ViRu)2 with the strong organic acceptors 2,3-dichloro-5,6-dicyano-1,4-benzoquinone, tetracyano-p-benzoquinodimethane (TCNQ), and F4TCNQ resulted in formation of the DBTTF-(ViRu)2•+ radical cation, as shown by various spectroscopic techniques. Solid samples of these compounds were found to be highly amorphous and electrically insulating.

Organic binary charge-transfer compounds of 2,2' : 6',2'' : 6'',6-trioxotriphenylamine and a pyrene-annulated azaacene as donors.

Three binary charge-transfer (CT) compounds resulting from the donor 2,2' : 6',2'' : 6'',6-trioxotriphenylamine (TOTA) and the acceptors F4TCNQ and F4BQ and of a pyrene-annulated azaacene (PAA) with the acceptor F4TCNQ are reported. The identity of these CT compounds are confirmed by single-crystal X-ray diffraction as well as by IR, UV-vis-NIR and EPR spectroscopy. X-ray diffraction analysis reveals a 1 : 1 stoichiometry for TOTA·F4TCNQ, a 2 : 1 donor : acceptor ratio in (TOTA)2·F4BQ, and a rare 4 : 1 stoichiometry in (PAA)4·F4TCNQ, respectively. Metrical parameters of the donor (D) and acceptor (A) constituents as well as IR spectra indicate full CT in TOTA·F4TCNQ, partial CT in (TOTA)2·F4BQ and only a very modest one in (PAA)4·F4TCNQ. Intricate packing motifs are present in the crystal lattice with encaged, π-stacked (F4TCNQ-)2 dimers in TOTA·F4TCNQ or mixed D/A stacks in the other two compounds. Their solid-state UV-vis-NIR spectra feature CT transitions. The CT compounds with F4TCNQ are electrical insulators, while (TOTA)2·F4BQ is weakly conducting.

Directing energy transfer in Pt(bodipy)(mercaptopyrene) dyads.

We report on the photophysical properties of three dyads that combine a 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (bodipy, BDP) and a mercaptopyrene (SPyr) dye ligand at a Pt(PEt3)2 fragment. σ-Bonding of the dyes to the Pt ion promotes intersystem crossing (ISC) via the external heavy atom effect. The coupling of efficient ISC with charge-transfer from the electron-rich mercaptopyrene to the electron-accepting BDP ligand (PB-CT) gives rise to a multitude of (potentially) emissive states. This culminates in the presence of four different emissions for the mono- and dinuclear complexes BPtSPyr and BPtSPyrSPtB with an unsubstituted BDP ligand and either a terminal 1-mercaptopyrene or a bridging pyrene-1,6-dithiolate ligand. Thus, in fluid solution, near IR emission at 724 nm from the 3PB-CT state is observed with a quantum yield of up to 15%. Excitation into the BDP-based 1ππ* or the pyrene-based 1ππ* band additionally trigger fluorescence and phosphorescence emissions from the BDP-centred 1ππ* and 3ππ* states. In frozen solution, at 77 K, phosphorescence from the pyrene ligand becomes the prominent emission channel, while PB-CT emission is absent. Alkylation of the BDP ligand in KBPtSPyr funnels all excitation energy into fluorescence and phosphorescence emissions from the KBDP ligand. The assignments of the various excited states and the deactivation cascades were probed by absorption and emission spectroscopy, transient absorption spectroscopy, electrochemical and UV/Vis/NIR spectroelectrochemical measurements, and by quantum chemical calculations. Our conclusions are further corroborated with the aid of suitable reference compounds comprising of just one chromophore. All dyads are triplet sensitizers and are able to generate singlet oxygen.

Four different emissions from a Pt(Bodipy)(PEt3)2(S-Pyrene) dyad.

The Pt(bodipy)-(mercaptopyrene) dyad BPtSPyr shows four different emissions: intense near-infrared phosphorescence (Φph up to 15%) from a charge-transfer state pyrS˙+-Pt-BDP˙-, additional fluorescence and phosphorescence emissions from the 1ππ* and 3ππ* states of the bodipy ligand at r.t., and phosphorescence from the pyrene 3ππ* and the bodipy 3ππ* states in a glassy matrix at 77 K.