Exploiting exciton coupling of ligand radical intervalence charge transfer transitions to tune NIR absorption

We detail the rational design of a series of bimetallic bis-ligand radical Ni salen complexes in which the relative orientation of the ligand radical chromophores provides a mechanism to tune the energy of intense intervalence charge transfer (IVCT) bands in the near infrared (NIR) region.

We detail the rational design of a series of bimetallic bis-ligand radical Ni salen complexes in which the relative orientation of the ligand radical chromophores provides a mechanism to tune the energy of intense intervalence charge transfer (IVCT) bands in the near infrared (NIR) region. Through a suite of experimental (electrochemistry, electron paramagnetic resonance spectroscopy, UV-vis-NIR spectroscopy) and theoretical (density functional theory) techniques, we demonstrate that bimetallic Ni salen complexes form bis-ligand radicals upon two-electron oxidation, whose NIR absorption energies depend on the geometry imposed in the bis-ligand radical complex. Relative to the oxidized monomer [1˙]⁺ (E = 4500 cm^–1, ε = 27 700 M^–1 cm^–1), oxidation of the cofacially constrained analogue 2 to [2˙˙]²⁺ results in a blue-shifted NIR band (E = 4830 cm^–1, ε = 42 900 M^–1 cm^–1), while oxidation of 5 to [5˙˙]²⁺, with parallel arrangement of chromophores, results in a red-shifted NIR band (E = 4150 cm^–1, ε = 46 600 M^–1 cm^–1); the NIR bands exhibit double the intensity in comparison to the monomer. Oxidation of the intermediate orientations results in band splitting for [3˙˙]²⁺ (E = 4890 and 4200 cm^–1; ε = 26 500 and 21 100 M^–1 cm^–1), and a red-shift for [4˙˙]²⁺ using ortho- and meta-phenylene linkers, respectively. This study demonstrates for the first time, the applicability of exciton coupling to ligand radical systems absorbing in the NIR region and shows that by simple geometry changes, it is possible to tune the energy of intense low energy absorption by nearly 400 nm.

Azadipyrromethenes: from traditional dye chemistry to leading edge applications

The journey of azadipyrromethenes from accidental dye chemistry to a compound class with widely applicable near infrared photophysical properties is documented.

Azadipyrromethene cyclometalation in neutral RuII complexes: photosensitizers with extended near-infrared absorption for solar energy conversion applications

In the on-going quest to harvest near-infrared (NIR) photons for energy conversion applications, a novel family of neutral ruthenium(ii) sensitizers has been developed by cyclometalation of an azadipyrromethene chromophore.

Twofac-tricarbonylrhenium(I) azadipyrromethene (ADPM) complexes: ligand-substitution effect on crystal structure

The crystal structures offac-(acetonitrile-κN)(2-{[3,5-bis(4-methoxyphenyl)-2H-pyrrol-2-ylidene-κN1]amino}-3,5-bis(4-<!?tlsb=0.2pt>methoxyphenyl)-1H-pyrrol-1-ido-κN1)tricarbonylrhenium(I)–hexane–acetonitrile (2/1/2), [Re(C36H30N3O4)(CH3CN)(CO)3]·0.5C6H14·CH3CN, (2), andfac-(2-{[3,5-bis(4-methoxyphenyl)-2H-pyrrol-2-ylidene-κN1]amino}-3,5-bis(4-methoxyphenyl)-1H-pyrrol-1-ido-κN1)tricarbonyl(dimethyl sulfoxide-κO)rhenium(I), [Re(C36H30N3O4)(C2H6OS)(CO)3], (3), at 150 K are reported. Both complexes display a distorted octahedral geometry, with afac-Re(CO)3arrangement and one azadipyrromethene (ADPM) chelating ligand in the equatorial position. One solvent molecule completes the coordination sphere of the ReIcentre in the remaining axial position. The ADPM ligand shows high flexibility upon coordination, while retaining its π-delocalized nature. Bond length and angle analyses indicate that the differences in the geometry around the ReIcentre in (2) and (3), and those found in three reportedfac-Re(CO)3–ADPM complexes, are dictated mainly by steric factors and crystal packing. Both structures display intramolecular C—H...N hydrogen bonding. Intermolecular interactions of the Csp2—H...π and Csp2—H...O(carbonyl) types link the discrete monomers into extended chains.

Introducing asymmetry in tetradentate azadipyrromethene chromophores: a systematic study of the impact on electronic and photophysical properties

As analogues of the porphyrinoid and dipyrromethene families of dye, azadipyrromethene (ADPM) derivatives exhibit exciting photophysical properties.