The nature of the singlet and triplet excited states of a series of meso-to-meso ethyne-linked bis-(porphyrin) compounds was probed by electronic absorption, polarized pump-probe fluorescence, electron paramagnetic resonance (EPR), electroabsorption (Stark), and transient triplet-triplet absorption spectroscopic methods. Pump-probe fluorescence anisotropy experiments show that the presence of meso-ethynyl substituents drives a reorientation of orthogonal x-and y-polarized singlet excited states in the macrocycle frame of reference with respect to that evinced for conventional free-base porphyrin chromophores. Analogous experiments in conjugated bis(porphyrin) species bis [(5,5′,-10,20-bis[3′′,5′′-(di-tert -butyl)porphyryl]ethyne, and bis[5,5′,-10,20-bis[3′′,5′′-(di-tert-butyl)phenyl]porphyryl]ethyne demonstrate substantial energetic splittings of the x-and y-polarized S 1 states. The magnitude of this energetic gap results in the complete suppression of population exchange between excited states having orthogonal polarizations on the time scale of these measurements, and gives rise to singly degenerate emitting states polarized exclusively along the axis defined by the ethyne moiety. Stark spectroscopic experiments show that the electronically symmetric mesoto-meso ethyne-bridged bis[(porphinato)zinc(II)] complex exhibits changes in dipole moment with respect to the ground state in its respective x-polarized S 2 and S 1 states. The EPR spectra of the low-lying photoexcited triplet excited states of these conjugated bis(porphyrin) compounds and their ethyne-substituted porphyrinic building blocks show an evolution in the |D| and |E| ZFS parameters with augmented conjugation consistent with a progressing oblate-to-prolate spin transition that causes the direction of largest dipolar interaction to align along the vector defined by the conjugated ethyne moiety. Conjugated arrays based on meso-ethyne elaborated porphyrin and (porphinato)zinc(II) precursors thus constitute an unusual class of oligomeric porphyrin species in that once a threshold level of conjugation is reached, the optical and magnetic principal axis systems become coincident.

This report describes the synthesis, characterization, and in vivo testing of several bifunctional contrast-enhancing agents for optical and magnetic resonance imaging (MRI) of experimental animals. These new agents integrate the advantages of both techniques since they can be visualized simultaneously by light and MRI microscopy. Employing this strategy allows the same biological structures of a specimen to be studied at dramatically different resolutions and depths. The complexes possess a metal chelator for binding a paramagnetic ion, gadolinium (Gd3+), and a covalently attached fluorescent dye. The first class of complexes are low-molecular weight species that are composed of the macrocyclic tetraamine 1,4,7,10-tetraazacyclododecane-N,N',N",N"'-tetraacetic acid (DOTA) as the metal-chelating ligand coupled to tetramethylrhodamine. The second class of MRI-enhancing agents are composed of high-molecular weight polymers that are membrane impermeable and once injected into a cell or cells are trapped inside. These complexes possess multiple copies of both the metal-chelator-diethylenetriaminepentaacetic acid (DTPA) and the tetramethylrhodamine attached to a macromolecular framework of either poly(D-lysine) (pdl) or dextran. Images acquired of single cells after injection with these bifunctional agents enabled us to follow the relative motions and reorganizations of different cell layers during amphibian gastrulation and neurulation in Xenopus laevis embryos.

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In aqueous media, hydrophobic metallocorroles form nanoparticles that are potential theranostic anticancer agents. We have analyzed the electronic and Raman spectra of Al­(III), Ga­(III), and Au­(III) corrole nanoparticles (and made comparisons with DFT-validated assignments of the IR spectra of corresponding monomers) in order to estimate the strengths of corrole–corrole electronic couplings in these assemblies. We find that these spectra are virtually unchanged upon aggregation, confirming that the intermolecular interactions in these nanoparticles are very weak.