Conjugates, Complexes, and Interlocked Systems Based on Squaraines and Cyanines - Advanced Fluorescence Reporters in Chemistry and Biology - page 178

1.0 1.0

22b ⊂ Rp 22b ⊂ Rp

0.8 0.8

22b

0.6 0.6

0.4 0.4

22b

0.2 0.2

0.0 0.0

0 50 100 150 0 20 40 60

Time [min] Time [min]

Fig. 10 Comparison of relative intensity changes of 22b and 22b Rp upon exposure to a 0.5%

hydrogen peroxide solution (a) and in presence of NaOH solution pH 13 (b)[ 60 ]

O

R R 23a : R = Et

23b

: R = n -Pr

N N

23c : R = n -Bu

R R

23 O

O O

O O

N

N

NH HN

NH HN

*

*

*

NH HN

NH HN *

N

N

O O O O

24a 24b

The clipping reaction used in [ 52 , 53 , 55 ] to synthesize tetralactam-based
squaraine rotaxanes such as 14 and 15 afforded only moderate yields (ca.
28-35%) of the rotaxanes, possibly because of the unavoidable presence of nucleo-
philes that react with the chemically unstable squaraines during the reaction. The
slippage approach [ 62 ] minimizes the squaraine dye's contact with nucleophiles
during the rotaxane formation process and therefore can be used to efficiently
encapsulate a squaraine dye such as 23 in a macrocycle such as 25 [ 63 ].
Formation of squaraine-pseudorotaxanes can be used to develop selective
chemosensors :Na + ions behave as highly selective templates, relative to other

Table 6 Spectral characteristics of squaraines and squaraine rotaxanes in chloroform
Dye l max Ab (nm) log e l max Em (nm) F M F

23a 633 5.52 658 0.72

24a 23a 637 5.44 666 0.22

24b 23a 642 5.43 667 0.49