Applications of Fluorescent Displacement-Based ... - Jacobs University

Encapsulation of Volatile Hydrocarbons by Cucurbiturils CHAPTER 2
the inner space of such molecular containers can represent a completely new
phase of matter. [93,94]
R 1 R 2 N
O NR 1 R 2
R 1 R 1
R 3 R 3
COOR 4
Rhodamine 6G (Rh6G):
R 1 = H, R 2 = Et, R 3 = Me, R 4 = Et
Tetramethylrhodamine (TMR):
R 1 = R 2 = Me, R 3 = H, R 4 = H
Rhodamine 123 (Rh123):
R 1 = R 2 = R 3 = H, R 4 = Et
N
N
DBO
N
R 2
NR 2
n
Cyanine 3' (Cy3'):
R 1 = H, R 2 = (CH 2 ) 4 SO 3 – , n = 1
Cyanine 5' (Cy5'):
R 1 = H, R 2 = (CH2) 4 SO 3 – , n = 2
R 2 N
O NR 2
N
O
O
H 2 N
O NH 2
N
Pyronin Y (PyY): R = Me
Pyronin B (PyB): R = Et
Coumarin102 (C102)
Cresyl violet (CV)
Scheme 2.1.1. Structures of fluorescent dyes displaying fluorescence lifetimeenhancing
effects upon complexation by CB7.
The first consequence of the low CBn polarizability is reflected in the
photophysical properties of the encapsulated fluorescent dyes, specifically, with
respect to their longer fluorescence lifetimes, τ 0 , in low-polarizability
environments. This is due to the dependence of the radiative decay rate, k r , on the
square of the refractive index, n 2 (the Strickler-Berg equation), which in turn is
directly related to the polarizability of the environment, P = (n 2 –1) / (n 2 +2). [95]
The radiative decay rates of several fluorophores have been measured in the
presence of CB7, and extremely low values were extracted, while exceedingly
high fluorescence lifetimes were recorded. These experiments have in fact
provided the direct spectroscopic evidence for the earlier empirical correlation
between oscillator strength and polarizability. DBO, for instance, holds the world
record with respect to its fluorescence lifetime, which is above 1 µs in aqueous
solution. [96] Numerous fluorescent dyes, including the commercially relevant
rhodamines, coumarins, pyronins, oxazines, and cyanines, display their longest
fluorescence lifetimes ever recorded in the inside of the CB cavity, including
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