A Dinuclear Platinum(II) N4Py Complex: An Unexpected Coordination Mode For N4Py

The polypyridyl compound <i>N</i>,<i>N</i>-bis­(2-pyridylmethyl)-<i>N</i>-bis­(2-pyridyl)­methylamine (N4Py) acts as a bridging ligand and coordinates to two Pt­(II) ions giving an unexpected diplatinum­(II) complex, whose photophysical and anticancer properties were investigated

Evolution of Nonmirror Image Fluorescence Spectra in Conjugated Polymers and Oligomers

The nonmirror image relationship between absorption and fluorescence spectra of conjugated polymers contrasts with most organic chromophores and is widely considered a signature of interchromopohore energy funneling. We apply broad-band ultrafast fluorescence spectroscopy to resolve the evolution of fluorescence spectra for dilute solutions of conjugated oligothiophenes, where no energy transfer is possible. Fluorescence spectra evolve from a mirror image of absorption, which lacks vibronic structure, toward a spectrally narrower and vibronically structured species on the hundreds of femtosecond to early picosecond time scale. Our analysis of this fluorescence spectral evolution shows that a broad distribution of torsional conformers is driven to rapidly planarize in the excited state, including in solid films, which is supported by Raman spectroscopy and quantum chemical modeling. Our data have important implications for understanding different energy-transfer regimes that are delineated by structural relaxation

Comparison of Inverse and Regular 2‑Pyridyl-1,2,3-triazole “Click” Complexes: Structures, Stability, Electrochemical, and Photophysical Properties

Two inverse 2-pyridyl-1,2,3-triazole “click” ligands, 2-(4-phenyl-1<i>H</i>-1,2,3-triazol-1-yl)­pyridine and 2-(4-benzyl-1<i>H</i>-1,2,3-triazol-1-yl)­pyridine, and their palladium­(II), platinum­(II), rhenium­(I), and ruthenium­(II) complexes have been synthesized in good to excellent yields. The properties of these inverse “click” complexes have been compared to the isomeric regular compounds using a variety of techniques. X-ray crystallographic analysis shows that the regular and inverse complexes are structurally very similar. However, the chemical and physical properties of the isomers are quite different. Ligand exchange studies and density functional theory (DFT) calculations indicate that metal complexes of the regular 2-(1-<b>R</b>-1<i>H</i>-1,2,3-triazol-4-yl)­pyridine (<b>R</b> = phenyl, benzyl) ligands are more stable than those formed with the inverse 2-(4-<b>R</b>-1<i>H</i>-1,2,3-triazol-1-yl)­pyridine (<b>R</b> = phenyl, benzyl) “click” chelators. Additionally, the <i>bis</i>-2,2′-bipyridine (bpy) ruthenium­(II) complexes of the “click” chelators have been shown to have short excited state lifetimes, which in the inverse triazole case, resulted in ejection of the 2-pyridyl-1,2,3-triazole ligand from the complex. Under identical conditions, the isomeric regular 2-pyridyl-1,2,3-triazole ruthenium­(II) bpy complexes are photochemically inert. The absorption spectra of the inverse rhenium­(I) and platinum­(II) complexes are red-shifted compared to the regular compounds. It is shown that conjugation between the substituent group <b>R</b> and triazolyl unit has a negligible effect on the photophysical properties of the complexes. The inverse rhenium­(I) complexes have large Stokes shifts, long metal-to-ligand charge transfer (MLCT) excited state lifetimes, and respectable quantum yields which are relatively solvent insensitive

Thermochromism, Franck–Condon Analysis and Interfacial Dynamics of a Donor–Acceptor Copolymer with a Low Band Gap

The electronic properties of the donor–acceptor (DA) polymer poly­{5,6-bis­(octyloxy)-4-(thiophen-2-yl)­benzo­[<i>c</i>]-1,2,5-thiadiazole} (PTBT) have been investigated using spectroscopic and computational techniques. Electronic absorption and emission spectra reveal the presence of an ordered and a disordered phase in solution. Franck–Condon modeling of the ordered phase yields Huang–Rhys factors of 0.55 (20 °C) and 0.51 (−180 °C), indicating little structural distortion between ground and excited state. DFT calculations with resonance Raman spectroscopy are consistent with a lowest energy excited state that is electronically delocalized and has little charge-transfer character, unexpected for a copolymer with a low bandgap (∼1.8 eV). Transient absorption spectroscopy of PTBT:fullerene blends reveals near-unity internal charge-transfer yields in both ordered and disordered film morphologies. In the disordered blend, charge transfer is complete within the laser pulse (100 fs), whereas the ordered blend also features a slower phase due to exciton diffusion in the phase separated morphology. In the ordered blend, the spectra and dynamics of charge transfer reveal that excitons and charges promptly occupy delocalized states on extended polymer chains. The pervasive use of donor–acceptor structures in polymer devices makes understanding the interplay of morphology and electronic structure of these polymers essential and here a spectroscopic and computational investigation gives an extensive picture of the electronic properties and their effect on charge dynamics in a DA polymer

Excited States of Triphenylamine-Substituted 2‑Pyridyl-1,2,3-triazole Complexes

A new 2-pyridyl-1,2,3-triazole (pytri) ligand, TPA-pytri, substituted with a triphenylamine (TPA) donor group on the 5 position of the pyridyl unit was synthesized and characterized. Dichloroplatinum­(II), bis­(phenylacetylide)­platinum­(II), bromotricarbonylrhenium­(I), and bis­(bipyridyl)­ruthenium­(II) complexes of this ligand were synthesized and compared to complexes of pytri ligands without the TPA substituent. The complexes of unsubstituted pytri ligands show metal-to-ligand charge-transfer (MLCT) absorption bands involving the pytri ligand in the near-UV region. These transitions are complemented by intraligand charge-transfer (ILCT) bands in the TPA-pytri complexes, resulting in greatly improved visible absorption (λ_max = 421 nm and ϵ = 19800 M^–1 cm^–1 for [Pt­(TPA-pytri)­Cl₂]). The resonance Raman enhancement patterns allow for assignment of these absorption bands. The [Re­(TPA-pytri)­(CO)₃Br] and [Pt­(TPA-pytri)­(CCPh)₂] complexes were examined with time-resolved infrared spectroscopy. Shifts in the CC and CO stretching bands revealed that the complexes form states with increased electron density about their metal centers. [Pt­(TPA-pytri)­Cl₂] is unusual in that it is emissive despite the presence of deactivating d–d states, which prevents emission from the unsubstituted pytri complex

Excited States of Triphenylamine-Substituted 2‑Pyridyl-1,2,3-triazole Complexes

A new 2-pyridyl-1,2,3-triazole (pytri) ligand, TPA-pytri, substituted with a triphenylamine (TPA) donor group on the 5 position of the pyridyl unit was synthesized and characterized. Dichloroplatinum­(II), bis­(phenylacetylide)­platinum­(II), bromotricarbonylrhenium­(I), and bis­(bipyridyl)­ruthenium­(II) complexes of this ligand were synthesized and compared to complexes of pytri ligands without the TPA substituent. The complexes of unsubstituted pytri ligands show metal-to-ligand charge-transfer (MLCT) absorption bands involving the pytri ligand in the near-UV region. These transitions are complemented by intraligand charge-transfer (ILCT) bands in the TPA-pytri complexes, resulting in greatly improved visible absorption (λ_max = 421 nm and ϵ = 19800 M^–1 cm^–1 for [Pt­(TPA-pytri)­Cl₂]). The resonance Raman enhancement patterns allow for assignment of these absorption bands. The [Re­(TPA-pytri)­(CO)₃Br] and [Pt­(TPA-pytri)­(CCPh)₂] complexes were examined with time-resolved infrared spectroscopy. Shifts in the CC and CO stretching bands revealed that the complexes form states with increased electron density about their metal centers. [Pt­(TPA-pytri)­Cl₂] is unusual in that it is emissive despite the presence of deactivating d–d states, which prevents emission from the unsubstituted pytri complex