Time-resolved EPR spectra of the triplet excited states of diaminoacridine guests in polar potassium hydrogen phthalate single crystals

Bellinazzi, Marco; Barbon, Antonio; Kahr, Bart; Benedict, Jason B.; Brustolon, Marina

doi:10.1039/b510076c

Cited by 5 publications

(5 citation statements)

References 12 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Previously, we recorded the TR-EPR spectra of diaminoacridine in KAP crystals . Data was taken from small, whole crystals.…”

Section: Discussionmentioning

confidence: 99%

“…Given the possibility of DCM protonation, we calculated the ZFS tensors for the triplet state of DCM and DCMH + in the A and B conformers according to the point dipole approximation and spin densities from the AM1 method (Table ) . Calculations of ZFS for dyes with heteroatoms are known to underestimate these parameters by about 10−20%. However, in the present case the difference between calculated and experimental parameters for the triplet of DCM is too large to be attributed to the approximation of the calculation method.…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Triplet States of the Nonlinear Optical Chromophore DCM in Single Crystals of Potassium Hydrogen Phthalate and Their Relationship to Single-Molecule Dark States

et al. 2009

Self Cite

View full text Add to dashboard Cite

Single-molecule dark states are often attributed to photoexcited triplets with scant evidence of the participation of paramagnetic molecules. The photodynamics of blinking single molecules of 4-dicyanomethylene-2-methyl-6-p-dimethylaminostyryl-4H-pyran (DCM) in crystals of potassium hydrogen phthalate (KAP) were compared with the lifetimes of DCM triplet states, likewise in KAP, whose zero-field splitting (ZFS) tensors were fully characterized by time-resolved electron paramagnetic resonance (TR-EPR) spectroscopy. Luminescent mixed crystals of KAP were grown from solutions containing 10(-4) -10(-9) M DCM, a model optically nonlinear chromophore. The luminescent dye was localized in the {111} crystalline growth sectors. The photoexcited triplets states of DCM in the heavily dyed (10(-4) M) crystals were analyzed by TR-EPR spectroscopy. The photoexcited singlet states of DCM in lightly dyed crystals (10(-9) M) were analyzed by single-molecule microscopy. Large blue shifts in the absorption and emission spectra of DCM in KAP were interpreted as a consequence of protonation at the dimethylamino nitrogen atom, an assignment supported by calculations of the zero-field splitting (ZFS) tensors of molecules in their triplet states. Experimental ZFS tensors with eigenvalues comparable to those of the computed tensors were determined from the angular dependence of the EPR spectra of DCMH(+) triplets within KAP single crystals with respect to the applied magnetic field. Data from individual growth sectors failed to show magnetically equivalent site occupancies, evidence of the kinetic ordering during growth. The intermittent fluorescence of individual chromophores was analyzed. The distributions of on(off) times were characterized by distributed rates fit to power laws. The lifetime of the triplet states was analyzed from the time decay of the EPR signals between 100 and 165 K. The data were well fit with a single time constant for the signal decay, a result wholly inconsistent with the blinking of single molecules with off times commonly of tens of seconds. Triplet decay was extrapolated to approximately 25 micros at room temperature. Therefore, the assumption that single-molecule dark states originate with triplet excited states is not sustainable for single DCM molecules in KAP.

show abstract

“…Previously, we recorded the TR-EPR spectra of diaminoacridine in KAP crystals . Data was taken from small, whole crystals.…”

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Triplet States of the Nonlinear Optical Chromophore DCM in Single Crystals of Potassium Hydrogen Phthalate and Their Relationship to Single-Molecule Dark States

et al. 2009

Self Cite

View full text Add to dashboard Cite

show abstract

“…Most any transparent crystal may become linearly dichroic by orienting and overgrowing anisotropic, colored additives: dyes. The subsequent, intermittent study of dyed crystals mimicked the sporadic analysis of optical anomalies. Curiously, the dyeing of crystals never developed as a craft at any time in human history, and this general and often beautiful aspect of supramolecular chemistry never became a sustained scientific inquiry, despite the ease and integrity with which simple crystalline substances can be colored with both natural and synthetic dyes …”

Section: Linear Dichroismmentioning

confidence: 99%

“…Dyes were used to selectively recognize different phases of a given compound (polymorphs), symmetry independent facets of a given crystal, and even enantiomorphous faces when the additive is chiral. ,, Optically responsive molecules were used as probes of local interactions with distinct crystallographic surfaces. For instance, crystals grown in the presence of luminophores with varying protonation states showed distinct luminescence energies depending upon the electrostatic potentials of the surfaces of the growth sectors to which they were associated . Dyes distinguished vicinal facets of emergent growth hillocks as in Figure .…”

Section: Linear Dichroismmentioning

confidence: 99%

Crystals in Light

2010

Self Cite

View full text Add to dashboard Cite

We have made images of crystals illuminated with polarized light for almost two decades. Early on, we abandoned photosensitive chemicals in favor of digital electrophotometry with all of the attendant advantages of quantitative intensity data. Accurate intensities are a boon because they can be used to analytically discriminate small effects in the presence of larger ones. The change in the form of our data followed camera technology that transformed picture taking the world over. Ironically, exposures in early photographs were presumed to correlate simply with light intensity, raising the hope that photography would replace sensorial interpretation with mechanical objectivity and supplant the art of visual photometry. This was only true in part. Quantitative imaging accurate enough to render the separation of crystalloptical quantities had to await the invention of the solid-state camera. Many pioneers in crystal optics were also major figures in the early history of photography. We draw out the union of optical crystallography and photography because the tree that connects the inventors of photography is a structure unmatched for organizing our work during the past 20 years, not to mention that silver halide crystallites used in chemical photography are among the most consequential "crystals in light", underscoring our title. We emphasize crystals that have acquired optical properties such as linear birefringence, linear dichroism, circular birefringence, and circular dichroism, during growth from solution. Other crystalloptical effects were discovered that are unique to curiously dissymmetric crystals containing embedded oscillators. In the aggregate, dyed crystals constitute a generalization of single crystal matrix isolation. Simple crystals provided kinetic stability to include guests such as proteins or molecules in excited states. Molecular lifetimes were extended for the preparation of laser gain media and for the study of the photodynamics of single molecules. Luminophores were used as guests in crystals to reveal aspects of growth mechanisms by labeling surface structures such as steps and kinks. New methods were adopted for measuring and imaging the optical rotatory power of crystals. Chiroptical anisotropies can now be compared with the results of quantum chemical calculations that have emerged in the past 10 years. The rapid determination of the optical rotation and circular dichroism tensors of molecules in crystals, and the interpretation of these anisotropies, remains a subject of future research. Polycrystalline patterns that form far from equilibrium challenged the quantitative interpretation of micrographs when heterogeneities along the optical path and obliquely angled interfaces played large roles. Resulting "artifacts" were nevertheless incisive probes of polycrystalline texture and mesoscale chemistry in simple substances grown far from equilibrium or in biopathological crystals such as Alzheimer's amyloid plaques.

show abstract

“…Quantum chemical methods are essential for determining the relative energies of tautomers, 129 as in the case of methyl red in phthalic acid, and well as for dyes that differ in their states of protonation. 130,131 Quantum based methods are also essential for fixing transition moments of dyes so as to reckon orientation on the basis of the disposition of moments with respect to the coordinate system of the chromophores. Such information is essential for interpreting the results of linear dichroism measurements.…”

Section: Computationmentioning

confidence: 99%