3 research outputs found
Photoinduced Energy and Electron-Transfer Reactions by Polypyridine Ruthenium(II) Complexes Containing a Derivatized Perylene Diimide
The
[RuĀ(II) (phen)<sub>2</sub>(pPDIp)]<sup>2+</sup> complex, where
pPDIp is the symmetric bridging ligand phenanthrolineāperyleneāphenanthroline,
shows strong electronic absorption bands attributed to the pPDIp and
{RuĀ(phen)<sub>2</sub>}<sup>2+</sup> moieties in acetonitrile. The
charge-separated intermediate {RuĀ(III) (phen)<sub>2</sub>(pPDIp<sup>āā¢</sup>)} was detected by transient absorption spectroscopy
upon electronic excitation in either the pPDIp or the complex moieties.
The charge-separated intermediate species decays to generate the triplet
state <sup>3</sup>*pPDIp-RuĀ(II) (Ļ<sub>P</sub> = 1.8 Ī¼s)
that sensitizes the formation of singlet molecular oxygen with quantum
yield Ļ<sub>Ī</sub> = 0.57. The dyad in deaerated acetonitrile
solutions is reduced by triethylamine (NEt<sub>3</sub>) to the [RuĀ(II)
(phen)<sub>2</sub>(pPDIp<sup>ā¢ā</sup>)] radical anion
in the dark. The electron-transfer reaction is accelerated by light
absorption. By photolysis of the radical anion, a second electron
transfer reaction occurs to generate the [RuĀ(II) (phen)<sub>2</sub>(pPDIp<sup>2ā</sup>)] dianion. The changes of the color of
solution indicate the redox states of complexes and offer a sensitive
reporter of each stage of redox reaction from start to finish. The
reduced complexes can be converted to the initial complex, using methyl
viologen or molecular oxygen as an electron acceptor. The accumulation
of electrons in two well-separated steps opens promising opportunities
such as in catalysis
Excited-State Proton Transfer of Fluorescein Anion as an Ionic Liquid Component
Fluorescent
ionic liquids (FILs) incorporating the fluorescein
anion have been prepared by anion exchange of the parent quaternary
ammonium chloride (Quat<sup>+</sup>Cl<sup>ā</sup>) ionic liquid.
By controlling the molar ratio of fluorescein to Quat<sup>+</sup>Cl<sup>ā</sup>, ionic liquids incorporating different prototropic
forms of fluorescein were prepared. The 1:1 molar ratio ionic liquid
(FIL1) is essentially composed of monoanionic fluorescein, while dianionic
fluorecein is predominant in the FIL with a 1:2 molar ratio (FIL2).
The fluorescence excitation spectrum of FIL2 is markedly different
from its absorption spectrum. Absorption features the fluorescein
dianion, while the excitation spectrum is exclusively due to the monoanion.
In FIL1, the absorption and excitation spectra are both characteristic
of the monoanion. In both FILs, emission of the dianion is observed
upon excitation of the monoanion. This unusual behavior is interpreted
in the context of a fast deprotonation of the monoanion in the excited
state. The presence of residual water in the ionic liquid is important
for the proton transfer process. By lowering the pH of FIL1, the transient
proton transfer is inhibited, and the emission of the monoanion could
be observed. The FILs have completely different spectroscopic properties
from solvated fluorescein in Quat<sup>+</sup>Cl<sup>ā</sup>, where the prototropic equilibrium is shifted toward the neutral
forms
Nonlinear Emission of Quinolizinium-Based Dyes with Application in Fluorescence Lifetime Imaging
Charged
molecules based on the quinolizinum cation have potential
applications as labels in fluorescence imaging in biological media
under nonlinear excitation. A systematic study of the linear and nonlinear
photophysics of derivatives of the quinolizinum cation substituted
by either dimethylaniline or methoxyphenyl electron donors is performed.
The effects of donor strength, conjugation length, and symmetry in
the two-photon emission efficiency are analyzed in detail. The best
performing nonlinear fluorophore, with two-photon absorption cross
sections of 1140 GM and an emission quantum yield of 0.22, is characterized
by a symmetric D-Ļ-A<sup>+</sup>-Ļ-D architecture based
on the methoxyphenyl substituent. Application of this molecule as
a fluorescent marker in optical microscopy of living cells revealed
that, under favorable conditions, the fluorophore can be localized
in the cytoplasmatic compartment of the cell, staining vesicular shape
organelles. At higher dye concentrations and longer staining times,
the fluorophore can also penetrate into the nucleus. The nonlinearly
excited fluorescence lifetime imaging shows that the fluorophore lifetime
is sensitive to its location in the different cell compartments. Using
fluorescence lifetime microscopy, a multicolor map of the cell is
drafted with a single dye