11 research outputs found
Symmetry Breaking in Pyrrolo[3,2-b]pyrroles: Synthesis, Solvatofluorochromism and Two-photon Absorption
Five centrosymmetric and one dipolar pyrrolo[3,2-b]pyrroles, possessing either two or one strongly electron-withdrawing nitro group have been synthesized in a straightforward manner from simple building blocks. For the symmetric compounds, the nitroaryl groups induced spontaneous breaking of inversion symmetry in the excited state, thereby leading to large solvatofluorochromism. To study the origin of this effect, the series employed peripheral structural motifs that control the degree of conjugation via altering of dihedral angle between the 4-nitrophenyl moiety and the electron-rich core. We observed that for compounds with a larger dihedral angle, the fluorescence quantum yield decreased quickly when exposed to even moderately polar solvents. Reducing the dihedral angle (i.e., placing the nitrobenzene moiety in the same plane as the rest of the molecule) moderated the dependence on solvent polarity so that the dye exhibited significant emission, even in THF. To investigate at what stage the symmetry breaking occurs, we measured two-photon absorption (2PA) spectra and 2PA cross-sections (sigma(2PA)) for all six compounds. The 2PA transition profile of the dipolar pyrrolo[3,2-b]pyrrole, followed the corresponding one-photon absorption (1PA) spectrum, which provided an estimate of the change of the permanent electric dipole upon transition, approximate to 18D. The nominally symmetric compounds displayed an allowed 2PA transition in the wavelength range of 700-900nm. The expansion via a triple bond resulted in the largest peak value, sigma(2PA)=770GM, whereas altering the dihedral angle had no effect other than reducing the peak value two- or even three-fold. In the S0S1 transition region, the symmetric structures also showed a partial overlap between 2PA and 1PA transitions in the long-wavelength wing of the band, from which a tentative, relatively small dipole moment change, 2-7D, was deduced, thus suggesting that some small symmetry breaking may be possible in the ground state, even before major symmetry breaking occurs in the excited state.1111Ysciescopu
Laser-induced frequency tuning of Fourier-limited single-molecule emitters
The local interaction of charges and light in organic solids is the basis of
distinct and fundamental effects. We here observe, at the single molecule
scale, how a focused laser beam can locally shift by hundreds-time their
natural linewidth and in a persistent way the transition frequency of organic
chromophores, cooled at liquid helium temperatures in different host matrices.
Supported by quantum chemistry calculations, the results are interpreted as
effects of a photo-ionization cascade, leading to a stable electric field,
which Stark-shifts the molecular electronic levels. The experimental method is
then applied to a common challenge in quantum photonics, i.e. the independent
tuning and synchronization of close-by quantum emitters, which is desirable for
multi-photon experiments. Five molecules that are spatially separated by about
50 microns and originally 20 GHz apart are brought into resonance within twice
their linewidth. Combining this ability with an emission linewidth that is only
limited by the spontaneous decay, the system enables fabrication-free,
independent tuning of multiple molecules integrated on the same photonic chip.Comment: 15 pages, 5 figures. Supplementary Informations 23 pages, 13 figure
Synthesis and Photophysical Properties of N-Arylated Diketopyrrolopyrroles
The N-arylation of diketopyrrolopyrroles with aryl fluorides free of nitro groups was successfully achieved for the first time. Diketopyrrolopyrroles possessing 3,4-dimethoxyphenyl and benzofuryl substituents underwent reaction with, for example, pentafluoropyridine, in the presence of K2CO3 in N-methyl-2-pyrrolidone to give the desired products in moderate yields. Their photophysical properties in solution were found not to differ significantly from those of analogous N-alkylated diketopyrrolopyrroles, whereas in contrast to the latter compounds, they were found to possess fluorescence in the solid state. The photophysical properties of all compounds were rationalized by using time-dependent density functional theory
Photochemical Isomerizations of Thiosemicarbazide, a Matrix Isolation Study
Two thione conformers of monomeric thiosemicarbazide
were trapped
from the gas phase into a low-temperature Ar matrix. A phototransformation
converting the less stable form of the compound into the most stable
conformer was induced by irradiation with near-IR (λ = 1462
nm) or UV (λ > 320 nm) light. This photoeffect allowed separation
of the IR spectra of the observed thione forms. The structures of
both observed isomers were identified by comparison of the separated
experimental IR spectra with the spectra theoretically predicted for
two most stable forms of the compound. The population ratio of the
two conformers in an Ar matrix, prior to any irradiation, was estimated
to be equal â2:1. Irradiation of matrix-isolated thiosemicarbazide
with shorter-wavelength UV (λ > 270 nm) light induced a phototautomeric
reaction generating thiol forms of the compound
Photophysics of Derivatives of 3âHydroxybenzo[<i>c</i>]coumarin
The
photophysical studies of two phenols, derivatives of 3-hydroxybenzoÂ[<i>c</i>]Âcoumarin, were performed in <i>n</i>-nonane
matrix at 5 K. Unstructured fluorescence spectrum of the derivative
bearing a salicylaldehyde moiety, whose onset is shifted by ca. 3000
cm<sup>â1</sup> to lower energy in respect to that of absorption,
and short decay time of this emission (0.75 ns) suggested the occurrence
of excited-state intramolecular proton transfer (ESIPT). The experimental
results were interpreted with the aid of quantum chemistry calculations
performed with the DFT and TDDFT/B3LYP/6-31++GÂ(d,p) methods
Dipolar Dyes with a Pyrrolo[2,3-b]quinoxaline Skeleton Containing a Cyano Group and a Bridged Tertiary Amino Group: Synthesis, Solvatofluorochromism, and Bioimaging
Two strongly polarized dipolar chromophores possessing a cyclic tertiary amino group at one terminus of the molecule and a CN group at the opposite terminus were designed and synthesized. Their rigid skeleton contains the rarely studied pyrrolo[2,3-b]quinoxaline ring system. The photophysical properties of these regioisomeric dyes were different owing to differing pi conjugation between the CN group and the electron-donor moiety. These dipolar molecules showed very intense emission, strong solvatofluorochromism, and sufficient two-photon brightness for bioimaging. One of these regioisomeric dyes, namely, 11-carbonitrile-2,3,4,5,6,7-hexahydro-1H-3a, 8,13,13b-tetraazabenzo[b]cyclohepta[1,2,3-jk]fluorene, was successfully utilized in two-photon imaging of mouse organ tissues and showed distinct tissue morphology with high resolution.1189Nsciescopu
Symmetry Breaking in Pyrrolo[3,2-b]pyrroles: Synthesis, Solvatofluorochromism and Two-photon Absorption
Five centrosymmetric and one dipolar pyrrolo[3,2-b]pyrroles, possessing either two or one strongly electron-withdrawing nitro group have been synthesized in a straightforward manner from simple building blocks. For the symmetric compounds, the nitroaryl groups induced spontaneous breaking of inversion symmetry in the excited state, thereby leading to large solvatofluorochromism. To study the origin of this effect, the series employed peripheral structural motifs that control the degree of conjugation via altering of dihedral angle between the 4-nitrophenyl moiety and the electron-rich core. We observed that for compounds with a larger dihedral angle, the fluorescence quantum yield decreased quickly when exposed to even moderately polar solvents. Reducing the dihedral angle (i.e., placing the nitrobenzene moiety in the same plane as the rest of the molecule) moderated the dependence on solvent polarity so that the dye exhibited significant emission, even in THF. To investigate at what stage the symmetry breaking occurs, we measured two-photon absorption (2PA) spectra and 2PA cross-sections (sigma(2PA)) for all six compounds. The 2PA transition profile of the dipolar pyrrolo[3,2-b]pyrrole, followed the corresponding one-photon absorption (1PA) spectrum, which provided an estimate of the change of the permanent electric dipole upon transition, approximate to 18D. The nominally symmetric compounds displayed an allowed 2PA transition in the wavelength range of 700-900nm. The expansion via a triple bond resulted in the largest peak value, sigma(2PA)=770GM, whereas altering the dihedral angle had no effect other than reducing the peak value two- or even three-fold. In the S0S1 transition region, the symmetric structures also showed a partial overlap between 2PA and 1PA transitions in the long-wavelength wing of the band, from which a tentative, relatively small dipole moment change, 2-7D, was deduced, thus suggesting that some small symmetry breaking may be possible in the ground state, even before major symmetry breaking occurs in the excited state
A Large Starphene Comprising Pentacene Branches
International audienceStarphenes are attractive compounds due to their characteristic physicochemical properties that are inherited from acenes, making them interesting compounds for organic electronics and optics. However, the instability and low solubility of larger starphene homologs make their synthesis extremely challenging. Herein, we present a new strategy leading to pristine [16]starphene in preparative scale. Our approach is based on a synthesis of a carbonyl-protected starphene precursor that is thermally converted in a solid-state form to the neat [16]starphene, which is then characterised with a variety of analytical methods, such as 13C CP-MAS NMR, TGA, MS MALDI, UV-Vis and FTIR spectroscopy. Furthermore, high-resolution STM experiments unambiguously confirm its expected structure and reveal a moderate electronic delocalisation between the pentacene arms. Nucleus-independent chemical shifts NICS(1) are also calculated to survey its aromatic character