11 research outputs found
Double Alkylene-Strapped Diphenylanthracene as a Photostable and Intense Solid-State Blue-Emitting Material
We report the synthesis and photochemical and photophysical
properties
of double alkylene-strapped 9,10-diphenylanthracene derivatives <b>3a</b>–<b>c</b> (<b>a</b>: C6 strap, <b>b</b>: C7 strap, <b>c</b>: C8 strap) in which the reactive
central aromatic ring of the anthracene moiety is protected by the
double alkylene straps. Thus, <b>3a</b>–<b>c</b> were much more resistant to photochemical reactions than the parent
9,10-diphenylanthracene (DPA). Furthermore, <b>3b</b> in C<sub>6</sub>H<sub>12</sub> as well as in a cast film and the powder state
showed the highest fluorescence quantum yields among <b>3a</b>, <b>3b</b>, quadruple triethylsilyl-protected DPA <b>4</b>, and DPA, wherein the C7 strap in <b>3b</b> effectively serves
to block fluorescence self-quenching
Self-Assembled Molecular Gear: A 4:1 Complex of Rh(III)Cl Tetraarylporphyrin and Tetra(<i>p</i>‑pyridyl)cavitand
The components of
a 4:1 mixture of RhÂ(III)Cl tetrakisÂ(4-methylÂphenyl)Âporphyrin <b>1</b> and a bowl-shaped tetraÂ(4-pyridyl)Âcavitand <b>4</b> self-assemble into a 4:1 complex <b>1</b><sub>4</sub>•<b>4</b> via Rh–pyridyl axial coordination bonds. The single-crystal
X-ray diffraction analysis and variable-temperature (VT) <sup>1</sup>H NMR study of <b>1</b><sub>4</sub>•<b>4</b> indicated
that <b>1</b><sub>4</sub>•<b>4</b> behaves as a
quadruple interlocking gear with an inner space, wherein (i) four
subunits-<b>1</b> are gear wheels and four <i>p</i>-pyridyl groups in subunit-<b>4</b> are axes of gear wheels,
(ii) one subunit-<b>1</b> and two adjacent subunits-<b>1</b> interlock with one another cooperatively, and (iii) four subunits-<b>1</b> in <b>1</b><sub>4</sub>•<b>4</b> rotate
quickly at 298 K on the NMR time scale. Together, the extremely strong
porphyrin-Rh–pyridyl axial coordination bond, the rigidity
of the methylene-bridge cavitand as a scaffold of the pyridyl axes,
and the cruciform arrangement of the interdigitating <i>p</i>-tolyl groups as the teeth moiety of the gear wheels in the assembling <b>1</b><sub>4</sub>-unit make <b>1</b><sub>4</sub>•<b>4</b> function as a quadruple interlocking gear in solution. The
gear function of <b>1</b><sub>4</sub>•<b>4</b> was
also supported by the rotation behaviors of other 4:1 complexes: <b>2</b><sub>4</sub>•<b>4</b> and <b>3</b><sub>4</sub>•<b>4</b> obtained from RhÂ(III)Cl tetrakisÂ[4-(4-methylÂphenyl)Âphenyl]Âporphyrin <b>2</b> or RhÂ(III)Cl tetrakisÂ(3,5-dialkoxyÂphenyl)Âporphyrin <b>3</b> and <b>4</b> also served as quadruple interlocking
gears, whereas <b>1</b><sub>4</sub>•<b>5</b> obtained
from <b>1</b> and tetrakisÂ[4-(4-pyridyl)Âphenyl]Âcavitand <b>5</b> did not behave as a gear. The results of activation parameters
(Δ<i>H</i><sup>⧧</sup>, Δ<i>S</i><sup>⧧</sup>, and Δ<i>G</i><sup>⧧</sup>) obtained from Eyring plots based on line-shape analysis of the
VT <sup>1</sup>H NMR spectra of <b>1</b><sub>4</sub>•<b>4</b>, <b>2</b><sub>4</sub>•<b>4</b>, and <b>3</b><sub>4</sub>•<b>4</b> also support the interlocking
rotation (geared coupled rotation) mechanism
Double Alkylene-Strapped Diphenylanthracene as a Photostable and Intense Solid-State Blue-Emitting Material
We report the synthesis and photochemical and photophysical
properties
of double alkylene-strapped 9,10-diphenylanthracene derivatives <b>3a</b>–<b>c</b> (<b>a</b>: C6 strap, <b>b</b>: C7 strap, <b>c</b>: C8 strap) in which the reactive
central aromatic ring of the anthracene moiety is protected by the
double alkylene straps. Thus, <b>3a</b>–<b>c</b> were much more resistant to photochemical reactions than the parent
9,10-diphenylanthracene (DPA). Furthermore, <b>3b</b> in C<sub>6</sub>H<sub>12</sub> as well as in a cast film and the powder state
showed the highest fluorescence quantum yields among <b>3a</b>, <b>3b</b>, quadruple triethylsilyl-protected DPA <b>4</b>, and DPA, wherein the C7 strap in <b>3b</b> effectively serves
to block fluorescence self-quenching
Double Alkylene-Strapped Diphenylanthracene as a Photostable and Intense Solid-State Blue-Emitting Material
We report the synthesis and photochemical and photophysical
properties
of double alkylene-strapped 9,10-diphenylanthracene derivatives <b>3a</b>–<b>c</b> (<b>a</b>: C6 strap, <b>b</b>: C7 strap, <b>c</b>: C8 strap) in which the reactive
central aromatic ring of the anthracene moiety is protected by the
double alkylene straps. Thus, <b>3a</b>–<b>c</b> were much more resistant to photochemical reactions than the parent
9,10-diphenylanthracene (DPA). Furthermore, <b>3b</b> in C<sub>6</sub>H<sub>12</sub> as well as in a cast film and the powder state
showed the highest fluorescence quantum yields among <b>3a</b>, <b>3b</b>, quadruple triethylsilyl-protected DPA <b>4</b>, and DPA, wherein the C7 strap in <b>3b</b> effectively serves
to block fluorescence self-quenching
Double Alkylene-Strapped Diphenylanthracene as a Photostable and Intense Solid-State Blue-Emitting Material
We report the synthesis and photochemical and photophysical
properties
of double alkylene-strapped 9,10-diphenylanthracene derivatives <b>3a</b>–<b>c</b> (<b>a</b>: C6 strap, <b>b</b>: C7 strap, <b>c</b>: C8 strap) in which the reactive
central aromatic ring of the anthracene moiety is protected by the
double alkylene straps. Thus, <b>3a</b>–<b>c</b> were much more resistant to photochemical reactions than the parent
9,10-diphenylanthracene (DPA). Furthermore, <b>3b</b> in C<sub>6</sub>H<sub>12</sub> as well as in a cast film and the powder state
showed the highest fluorescence quantum yields among <b>3a</b>, <b>3b</b>, quadruple triethylsilyl-protected DPA <b>4</b>, and DPA, wherein the C7 strap in <b>3b</b> effectively serves
to block fluorescence self-quenching
Double Alkylene-Strapped Diphenylanthracene as a Photostable and Intense Solid-State Blue-Emitting Material
We report the synthesis and photochemical and photophysical
properties
of double alkylene-strapped 9,10-diphenylanthracene derivatives <b>3a</b>–<b>c</b> (<b>a</b>: C6 strap, <b>b</b>: C7 strap, <b>c</b>: C8 strap) in which the reactive
central aromatic ring of the anthracene moiety is protected by the
double alkylene straps. Thus, <b>3a</b>–<b>c</b> were much more resistant to photochemical reactions than the parent
9,10-diphenylanthracene (DPA). Furthermore, <b>3b</b> in C<sub>6</sub>H<sub>12</sub> as well as in a cast film and the powder state
showed the highest fluorescence quantum yields among <b>3a</b>, <b>3b</b>, quadruple triethylsilyl-protected DPA <b>4</b>, and DPA, wherein the C7 strap in <b>3b</b> effectively serves
to block fluorescence self-quenching
Stereospecific Synthesis of Tris-heteroleptic Tris-cyclometalated Iridium(III) Complexes via Different Heteroleptic Halogen-Bridged Iridium(III) Dimers and Their Photophysical Properties
Herein,
we report on the stereospecific synthesis of two single
isomers of tris-heteroleptic tris-cyclometalated iridiumÂ(III) (IrÂ(III))
complexes composed of three different nonsymmetric cyclometalating
ligands via heteroleptic halogen-bridged Ir dimers [IrÂ(tpy)Â(F<sub>2</sub>ppy)Â(μ-Br)]<sub>2</sub> <b>17b</b> and [IrÂ(mpiq)Â(F<sub>2</sub>ppy)Â(μ-Br)]<sub>2</sub> <b>27b</b> (tpyH:
(2-(4′-tolyl)ÂpyriÂdine) and F<sub>2</sub>ppyH: (2-(4′,6′-diÂfluoroÂphenyl)Âpyridine),
and mpiqH: (1-(4′-methylÂphenyl)ÂisoÂquinoline))
prepared by Zn<sup>2+</sup>-promoted degradation of IrÂ(tpy)<sub>2</sub>Â(F<sub>2</sub>ppy) <b>21</b> and IrÂ(mpiq)<sub>2</sub>Â(F<sub>2</sub>ppy) <b>26</b>, as reported by us.
Subsequently, <b>17b</b> and <b>27b</b> were converted
to the tris-heteroleptic tris-cyclometalated Ir complexes IrÂ(tpy)Â(F<sub>2</sub>ppy)Â(mpiq) <b>25</b> consisting of tpy, F<sub>2</sub>ppy, and mpiq, as confirmed by spectroscopic data and X-ray
crystal structure analysis. The first important point in this work
is the selective synthesis of specific isomers among eight possible
stereoisomers of Ir complexes having the same combination of three
cyclometalating ligands. Namely, two meridional forms of <b>25</b> were synthesized and isolated. The second finding is that the different
stereoisomers of <b>25</b> have different stability. Finally,
different stereoisomers exhibit different emission spectra. Namely,
one of its stereoisomers <b>25a</b> exhibits a single broad
emission from <i>ca</i>. 550 nm to <i>ca</i>.
650 nm (orange emission), while stereoisomer <b>25c</b> emits
dual emission at <i>ca</i>. 509 nm and <i>ca</i>. 600 nm (pale pink emission), as supported by time-dependent density
functional theory calculation. To the best of our knowledge, this
is the first report of the selective and efficient synthesis of different
stereoisomers of tris-heteroleptic tris-cyclometalated IrÂ(III) complexes
that have different stabilities and different photophysical properties
Pyrrole-Fused Azacoronene Family: The Influence of Replacement with Dialkoxybenzenes on the Optical and Electronic Properties in Neutral and Oxidized States
A novel
pyrrole-fused azacoronene family was synthesized via oxidative
cyclodehydrogenation of the corresponding hexaarylbenzenes as the
key step, and the crystal structures of tetraazacoronene <b>3b</b> and triazacoronene <b>4a</b> were elucidated. The photophysical
properties for neutral compounds <b>1</b>–<b>4</b> were investigated using steady-state UV–vis absorption/emission
spectroscopy and time-resolved spectroscopy (emission spectra and
lifetime measurements) at both room temperature and 77 K. The observation
of both fluorescence and phosphorescence allowed us to estimate the
small S<sub>1</sub>–T<sub>1</sub> energy gap (Δ<i>E</i><sub>S–T</sub>) to be 0.35 eV (<b>1a</b>),
0.26 eV (<b>2a</b>), and 0.36 eV (<b>4a</b>). Similar
to the case of previously reported hexapyrrolohexaazacoronene <b>1</b> (HPHAC), electrochemical oxidation revealed up to four reversible
oxidation processes for all of the new compounds. The charge and spin
delocalization properties of the series of azacoronene π-systems
were examined using UV–vis–NIR absorption, ESR, and
NMR spectroscopies for the chemically generated radical cations and
dications. Combined with the theoretical calculations, the experimental
results clearly demonstrated that the replacement of pyrrole rings
with dialkoxybenzene plays a critical role in the electronic communication,
where resonance structures significantly contribute to the thermodynamic
stability of the cationic charges/spins and determine the spin multiplicities.
For HPHAC <b>1</b> and pentaazacoronene <b>2</b>, the
overall aromaticity predicted for closed-shell dications <b>1</b><sup><b>2+</b></sup> and <b>2</b><sup><b>2+</b></sup> was primarily based on the theoretical calculations, and the
open-shell singlet biradical or triplet character was anticipated
for tetraazacoronene <b>3</b><sup><b>2+</b></sup> and
triazacoronene <b>4</b><sup><b>2+</b></sup> with the aid
of theoretical calculations. These polycyclic aromatic hydrocarbons
(PAHs) represent the first series of nitrogen-containing PAHs that
can be multiply oxidized
Pyrrole-Fused Azacoronene Family: The Influence of Replacement with Dialkoxybenzenes on the Optical and Electronic Properties in Neutral and Oxidized States
A novel
pyrrole-fused azacoronene family was synthesized via oxidative
cyclodehydrogenation of the corresponding hexaarylbenzenes as the
key step, and the crystal structures of tetraazacoronene <b>3b</b> and triazacoronene <b>4a</b> were elucidated. The photophysical
properties for neutral compounds <b>1</b>–<b>4</b> were investigated using steady-state UV–vis absorption/emission
spectroscopy and time-resolved spectroscopy (emission spectra and
lifetime measurements) at both room temperature and 77 K. The observation
of both fluorescence and phosphorescence allowed us to estimate the
small S<sub>1</sub>–T<sub>1</sub> energy gap (Δ<i>E</i><sub>S–T</sub>) to be 0.35 eV (<b>1a</b>),
0.26 eV (<b>2a</b>), and 0.36 eV (<b>4a</b>). Similar
to the case of previously reported hexapyrrolohexaazacoronene <b>1</b> (HPHAC), electrochemical oxidation revealed up to four reversible
oxidation processes for all of the new compounds. The charge and spin
delocalization properties of the series of azacoronene π-systems
were examined using UV–vis–NIR absorption, ESR, and
NMR spectroscopies for the chemically generated radical cations and
dications. Combined with the theoretical calculations, the experimental
results clearly demonstrated that the replacement of pyrrole rings
with dialkoxybenzene plays a critical role in the electronic communication,
where resonance structures significantly contribute to the thermodynamic
stability of the cationic charges/spins and determine the spin multiplicities.
For HPHAC <b>1</b> and pentaazacoronene <b>2</b>, the
overall aromaticity predicted for closed-shell dications <b>1</b><sup><b>2+</b></sup> and <b>2</b><sup><b>2+</b></sup> was primarily based on the theoretical calculations, and the
open-shell singlet biradical or triplet character was anticipated
for tetraazacoronene <b>3</b><sup><b>2+</b></sup> and
triazacoronene <b>4</b><sup><b>2+</b></sup> with the aid
of theoretical calculations. These polycyclic aromatic hydrocarbons
(PAHs) represent the first series of nitrogen-containing PAHs that
can be multiply oxidized
Pyrrole-Fused Azacoronene Family: The Influence of Replacement with Dialkoxybenzenes on the Optical and Electronic Properties in Neutral and Oxidized States
A novel
pyrrole-fused azacoronene family was synthesized via oxidative
cyclodehydrogenation of the corresponding hexaarylbenzenes as the
key step, and the crystal structures of tetraazacoronene <b>3b</b> and triazacoronene <b>4a</b> were elucidated. The photophysical
properties for neutral compounds <b>1</b>–<b>4</b> were investigated using steady-state UV–vis absorption/emission
spectroscopy and time-resolved spectroscopy (emission spectra and
lifetime measurements) at both room temperature and 77 K. The observation
of both fluorescence and phosphorescence allowed us to estimate the
small S<sub>1</sub>–T<sub>1</sub> energy gap (Δ<i>E</i><sub>S–T</sub>) to be 0.35 eV (<b>1a</b>),
0.26 eV (<b>2a</b>), and 0.36 eV (<b>4a</b>). Similar
to the case of previously reported hexapyrrolohexaazacoronene <b>1</b> (HPHAC), electrochemical oxidation revealed up to four reversible
oxidation processes for all of the new compounds. The charge and spin
delocalization properties of the series of azacoronene π-systems
were examined using UV–vis–NIR absorption, ESR, and
NMR spectroscopies for the chemically generated radical cations and
dications. Combined with the theoretical calculations, the experimental
results clearly demonstrated that the replacement of pyrrole rings
with dialkoxybenzene plays a critical role in the electronic communication,
where resonance structures significantly contribute to the thermodynamic
stability of the cationic charges/spins and determine the spin multiplicities.
For HPHAC <b>1</b> and pentaazacoronene <b>2</b>, the
overall aromaticity predicted for closed-shell dications <b>1</b><sup><b>2+</b></sup> and <b>2</b><sup><b>2+</b></sup> was primarily based on the theoretical calculations, and the
open-shell singlet biradical or triplet character was anticipated
for tetraazacoronene <b>3</b><sup><b>2+</b></sup> and
triazacoronene <b>4</b><sup><b>2+</b></sup> with the aid
of theoretical calculations. These polycyclic aromatic hydrocarbons
(PAHs) represent the first series of nitrogen-containing PAHs that
can be multiply oxidized