A newly synthesized hemicyanine dye,
trans-4-[p-[N-ethyl-N-(hydroxyethyl)amino]styryl]-N-methylpyridinium
tetraphenylborate (ASPT), has recently been shown to be an excellent
dye for both one- and two-photon-pumped lasing and for applications in optical power limiting. We
report on the absorption, one- and two-photon-induced emission, quantum yield, and the excited-state lifetime
of ASPT in different solvents of varying
polarity. We also present the spectral characteristics of ASPT
within a reverse-micelle and β-cyclodextrin
cavity. Our results demonstrate that ASPT is one of the few dyes
which exhibits highly solvent-polarity-dependent fluorescence in the useful orange-red region of the spectrum
(560−620 nm). Therefore, it offers
many applications in the biomedical field as a fluorescent probe
molecule. In addition, ASPT is fluorescent
upon excitation with an infrared (IR) source (two-photon-induced
emission) making it even more attractive,
since the background fluorescence from biological fluids upon IR
excitation is highly reduced compared to
ultraviolet or visible excitation. The solvatochromic effect of
ASPT is proposed to be due to a change in the
dipole moment and reduced hydrogen bonding effects of the dye upon
excitation. On the basis of our results,
we propose that ASPT exists in two mesomeric forms. One is
predominant in the ground-state and the other
in the excited-state. We observe a low quantum yield of the dye
(<10%) in all the investigated solvents.
The excited-state lifetime of ASPT is also observed to be
solvent-dependent (30−400 ps). The calculated
radiative decay rate is observed to remain constant but the
nonradiative decay rate increases in solvents of
increasing polarity. Finally, we report on the spectral feature of
ASPT within a reverse-micelle cavity with
varying water loadings and upon binding to a β-CD
cavity.
Dendrimeric polyphenylselenides are prepared in high yield using propyloxy spacers to connect the phenyseleno groups to the dendrimeric
core. The selenides catalyze the oxidation of bromide with hydrogen peroxide to give positive bromine species that can be captured by
cyclohexene in two-phase systems. The increase in the rate of catalysis exceeds statistical contributions for the first few generations with 3,
6, and 12 phenylseleno groups.
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