Conjugates, Complexes, and Interlocked Systems Based on Squaraines and Cyanines - Advanced Fluorescence Reporters in Chemistry and Biology - page 168

Encapsulation of 3,3 0 -diethyl-thiacarbocyanine iodide (DTCI)withCB7 resulted
in a fivefold increase of its quantum yield. The encapsulation decreases the 550 nm
peak in the absorption spectrum and increases the shoulder at 510 nm [ 47 ]. The
fluorescence lifetime for DTCI in aqueous solution is 0.12 ns, but in the presence of
CB7 it increased to 1.07 ns. The association constant of 1:1 complexes of DTCI with
CB7 was determined to be K 10 4 M 1 . ¼ (2.8 0.2)

R 2 R 2

S S

N N

I

DTCI Et

N
R 1

N

Et

n

R 1

12

: n =1, R 1 = Et, R 2 = SO 3 H
12b

: n = 2, R 1 = Et, R 2 = SO 3 H

12a 12c

: n =1, R 1 = -(CH 2 ) 4 SO 3 H, R 2 = H : n = 2, R 1 = -(CH 2 ) 4 SO 3 H, R 2 = H

12d

While the encapsulation of the trimethine dyes 12a and 12b (Cy3 analogs) leads
to red-shifted absorption and emission spectra, the maxima of the pentamethines
12c and 12d (Cy5 analogs) remain almost unchanged upon encapsulation (Table 2 ).
The fluorescence quantum yield and relative brightness of dyes 12c and 12d
substantially increase ( 1.7-fold) upon encapsulation in the CB7 macrocycle,
while the encapsulation of dye 12a is accompanied by a 1.3-1.5-fold decrease in
brightness [ 48 ]. The fluorescence lifetimes of 12b and 12d in water (0.46 and
0.63 ns) increase to 0.58 and 1.59 ns, respectively, after embedding in the CB7
macrocycle. The CB7 macrocycle was also suggested to protect dye molecules
from photobleaching: indeed the photostability of the 12a-CB7 and 12c-CB7
complexes increases slightly compared to that of the free dyes, but the reported
increases are small.
In summary, the encapsulation of cyanine dyes in CB7 causes either an increase
or a decrease in quantum yields and brightness but in general increases photo-
stability. Enhancements in fluorescence intensity by about one order of magnitude
or more were observed [ 46 ]. These fluorescence property changes are utilized for
the development of sensors , where the fluorescent dye may serve as a probe to
signal the binding of an analyte. No reports were found on the encapsulation of
squaraines in CBs.

Table 2 Effect of the addition of CB7 on the spectral characteristics and photostability of cyanine
dyes in water [ 46 , 48 ]
Dye

Without CB7 With 1 mM CB7

l max Ab (nm) l max Em (nm) F l max Ab (nm) l max Em (nm) F Stabilization

factor

F F

12a 545 560 0.15 559 571 0.108 1.4

12b 545 560 0.04 559 571 0.03 -

12c 642 660 0.27 642 657 0.456 1.3

12d 642 660 0.17 642 657 0.30 -