A previously reported dinuclear DNA imaging probe has been converted into a phototherapeutic through the incorporation of RuII(TAP)2 fragments (TAP = 1,4,5,8-3 tetraazaphenanthrene).

The synthesis of a new dinuclear complexes containing linked Ru II (dppz) and Re I (dppz) moieties is reported. The photophysical and biological properties of the new complex, which incorporates a N,N'-bis(4-pyridylmethyl)-1,6-hexanediamine tether ligand, are compared to a previously reported Ru II /Re I complex linked by a simple dipyridyl alkane ligand. Although both complexes bind to DNA with similar affinities, steady state and time resolved photophysical studies reveal that the nature of the linker affects the excited state dynamics of the complexes and their DNA photocleavage properties. Quantum based DFT calculations on these systems offers insights into these effects. Whilst both complexes are live cells permeant, their intracellular localization are significantly affected by the nature of the linker. Notably, one of the complexes displayed concentration dependent localization and possesses photophysical properties that are compatible with SIM and STED nanoscopy. This allowed the dynamics of its intracellular localization to be tracked at super resolutions.

By addressing the challenge of controlling molecular motion, mechanically interlocked molecular machines are primed for a variety of applications in the field of nanotechnology. Specifically, the designed manipulation of communication pathways between electron donor and acceptor moieties that are strategically integrated into dynamic photoactive rotaxanes and catenanes may lead to efficient artificial photosynthetic devices. In this pursuit, a novel [3]rotaxane molecular shuttle consisting of a four-station bis-naphthalene diimide (NDI) and central C fullerene bis-triazolium axle component and two mechanically bonded ferrocenyl-functionalized isophthalamide anion binding site-containing macrocycles is constructed using an anion template synthetic methodology. Dynamic coconformational anion recognition-mediated shuttling, which alters the relative positions of the electron donor and acceptor motifs of the [3]rotaxane's macrocycle and axle components, is demonstrated initially by H NMR spectroscopy. Detailed steady-state and time-resolved UV-vis-IR absorption and emission spectroscopies as well as electrochemical studies are employed to further probe the anion-dependent positional macrocycle-axle station state of the molecular shuttle, revealing a striking on/off switchable emission response induced by anion binding. Specifically, the [3]rotaxane chloride coconformation, where the ferrocenyl-functionalized macrocycles reside at the center of the axle component, precludes electron transfer to NDI, resulting in the switching-on of emission from the NDI fluorophore and concomitant formation of a C fullerene-based charge-separated state. By stark contrast, in the absence of chloride as the hexafluorophosphate salt, the ferrocenyl-functionalized macrocycles shuttle to the peripheral NDI axle stations, quenching the NDI emission via formation of a NDI-containing charge-separated state. Such anion-mediated control of the photophysical behavior of a rotaxane through molecular motion is unprecedented.

A heterometallic octanuclear coordination cage [Os4Zn4(Lnap)12]­X16 (denoted Os•Zn; X = perchlorate or chloride) has been prepared (Lnap is a bis-bidentate bridging ligand containing two pyrazolyl–pyridine chelating units separated by a 1,5-naphthalenediyl spacer group). The {Os­(NN)3}2+ units located at four of the eight vertices of the cube have a long-lived, phosphorescent 3MLCT excited state which is a stronger electron donor than [Ru­(bipy)3]2+. The chloride form of Os•Zn is water-soluble and binds in its central cavity the hydrophobic electron-accepting organic guests 1,2,4,5-tetracyanobenzene, 1,4-naphthoquinone and 1-nitronaphthalene, with binding constants in the range 103–104 M–1, resulting in quenching of the phosphorescence arising from the Os­(II) units. A crystal structure of an isostructural Co8 cage containing one molecule of 1,2,4,5-tetracyanobenzene as a guest inside the cavity has been determined. Ultrafast transient absorption measurements show formation of a charge-separated Os­(III)/guest•– state arising from cage-to-guest photoinduced electron transfer; this state is formed within 13–21 ps, and decays on a time scale of ca. 200 ps. In the presence of a competing guest with a large binding constant (cycloundecanone) which displaces each electron-accepting quencher from the cage cavity, the charge-separated state is no longer observed. Further, a combination of mononuclear {Os­(NN)3}2+ model complexes with the same electron-accepting species showed no evidence for formation of charge-separated Os­(III)/guest•– states. These two control experiments indicate that the {Os­(NN)3}2+ chromophores need to be assembled into the cage structure to bind the electron-accepting guests, and for PET to occur. These results help to pave the way for use of photoactive coordination cages as hosts for photoredox catalysis reactions on bound guests.

A detailed understanding of the dynamics of photoinduced processes occurring in the electronic excited state is essential in informing the rational design of photoactive transition-metal complexes. Here, the rate of intersystem crossing in a Cr(III)-centered spin-flip emitter is directly determined through the use of ultrafast broadband fluorescence upconversion spectroscopy (FLUPS). In this contribution, we combine 1,2,3-triazole-based ligands with a Cr(III) center and report the solutionstable complex [Cr(btmp) 2 ] 3+ (btmp = 2,6-bis(4-phenyl-1,2,3-triazol-1-yl-methyl)pyridine) (1 3+ ), which displays near-infrared (NIR) luminescence at 760 nm (τ = 13.7 μs, ϕ = 0.1%) in fluid solution. The excited-state properties of 1 3+ are probed in detail through a combination of ultrafast transient absorption (TA) and femtosecond-topicosecond FLUPS. Although TA spectroscopy allows us to observe the evolution of phosphorescent excited states within the doublet manifold, more significantly and for the first time for a complex of Cr(III), we utilize FLUPS to capture the short-lived fluorescence from initially populated quartet excited states immediately prior to the intersystem crossing process. The decay of fluorescence from the low-lying 4 MC state therefore allows us to assign a value of (823 fs) −1 to the rate of intersystem crossing. Importantly, the sensitivity of FLUPS to only luminescent states allows us to disentangle the rate of intersystem crossing from other closely associated excited-state events, something which has not been possible in the spectroscopic studies previously reported for luminescent Cr(III) systems.