Graft-through ring-opening metathesis polymerization (ROMP) using ruthenium N-heterocyclic carbene catalysts has enabled the synthesis of bottle-brush polymers with unprecedented ease and control. Here we report the first bivalent-brush polymers; these materials were prepared by graft-through ROMP of drug-loaded polyethylene-glycol (PEG) based macromonomers (MMs). Anticancer drugs doxorubicin (DOX) and camptothecin (CT) were attached to a norbornene-alkyne-PEG MM via a photocleavable linker. ROMP of either or both drug-loaded MMs generated brush homo- and co-polymers with low polydispersities and defined molecular weights. Release of free DOX and CT from these materials was initiated by exposure to 365 nm light. All of the CT and DOX polymers were at least 10-fold more toxic to human cancer cells after photoinitiated drug release while a copolymer carrying both CT and DOX displayed 30-fold increased toxicity upon irradiation. Graft-through ROMP of drug-loaded macromonomers provides a general method for the systematic study of structure-function relationships for stimuli-responsive polymers in biological systems.

Multichromophoric arrays provide one strategy for assembling molecules with intense absorptions across the visible spectrum but are generally focused on systems that efficiently produce and manipulate singlet excitations and therefore are burdened by the restrictions of (a) unidirectional energy transfer and (b) limited tunability of the lowest molecular excited state. In contrast, we present here a multichromophoric array based on four boron dipyrrins (BODIPY) bound to a platinum benzoporphyrin scaffold that exhibits intense panchromatic absorption and efficiently generates triplets. The spectral complementarity of the BODIPY and porphryin units allows the direct observation of fast bidirectional singlet and triplet energy transfer processes (k ST ( 1 BDPf 1 Por) ) 7.8 × 10 11 s -1 , k TT ( 3 Porf 3 BDP) ) 1.0 × 10 10 s -1 , k TT ( 3 BDPf 3 Por) ) 1.6 × 10 10 s -1 ), leading to a long-lived equilibrated [ 3 BDP][Por]h[BDP][ 3 Por] state. This equilibrated state contains approximately isoenergetic porphyrin and BODIPY triplets and exhibits efficient near-infrared phosphorescence (λ em ) 772 nm, Φ ) 0.26). Taken together, these studies show that appropriately designed triplet-utilizing arrays may overcome fundamental limitations typically associated with core-shell chromophores by tunable redistribution of energy from the core back onto the antennae.

The PdII dimers [(2-phenylpyridine)Pd(μ-X)]2 and [(2-p-tolylpyridine)Pd(μ-X)]2 (X = OAc or TFA) do not exhibit the expected planar geometry (of approximate D 2h symmetry) but instead resemble an open “clamshell” in which the acetate ligands are perpendicular to the plane containing the Pd atoms and 2-arylpyridine ligands, with the Pd atoms brought quite close to one another (approximate distance 2.85 Å). The molecules adopt this unusual geometry in part because of a d8−d8 bonding interaction between the two Pd centers. The Pd−Pd dimers exhibit two successive one-electron oxidations: PdII−PdII to PdII−PdIII to PdIII−PdIII. Photophysical measurements reveal clear differences in the UV−visible and low-temperature fluorescence spectra between the clamshell dimers and related planar dimeric [(2-phenylpyridine)Pd(μ-Cl)]2 and monomeric [(2-phenylpyridine)Pd(en)][Cl] (en = ethylenediamine) complexes that do not have any close Pd−Pd contacts. Density functional theory and atoms in molecules analyses confirm the presence of a Pd−Pd bonding interaction in [(2-phenylpyridine)Pd(μ-X)]2 and show that the highest occupied molecular orbital is a d z 2 σ* Pd−Pd antibonding orbital, while the lowest unoccupied molecular orbital and close-lying empty orbitals are mainly located on the 2-phenylpyridine rings. Computational analyses of other PdII−PdII dimers that have short Pd−Pd distances yield an orbital ordering similar to that of [(2-phenylpyridine)Pd(μ-X)]2, but quite different from that found for d8−d8 dimers of Rh, Ir, and Pt. This difference in orbital ordering arises because of the unusually large energy gap between the 4d and 5p orbitals in Pd and may explain why Pd d8−d8 dimers do not exhibit the distinctive photophysical properties of related Rh, Ir, and Pt species.

The photophysical properties of Ir(III) corroles differ from those of phosphorescent porphyrin complexes, cyclometalated and polyimine Ir(III) compounds, and other luminescent metallocorroles. Ir(III) corrole phosphorescence is observed at ambient temperature at wavelengths much longer (>800 nm) than those of most Ir(III) phosphors. The solvatochromic behavior of Ir(III)-corrole Soret and Q absorption bands suggests that the lowest singlet excited states (S2 and S1) are substantially more polar than the ground state.