Photophysics and Photochemistry of Molecular Recognition and Sensing with Metal-Directed Macrocyclic Systems - Molecular Self-Assembly: Advances and Applications - page 330

, showed strong
luminescence quenching with dipyridyl guests [51]. A nanomolar
solution of the square

The zinc(II) metallaporphyrin square, 45

was subjected to titration with the flexible
bipyridyl base bis-1,4-(4-ethylpyridyl)benzene (bpe). More than
90% of the porphyrin absorption intensity was quenched following
the addition of two equivalents of bpe to a solution of the square

45

45

in CH vis absorption spectrum showed a bathochromic

shift of the Soret and Q bands by ca. 10 nm, as expected for binding
to the Zn(II) porphyrin portions of the host. The fluorescence of
square

Cl . The UV

−

2 2

was also quenched on the addition of the dipyridyl guest.
The binding constant of bipyridine guest with square

45

45 was

∼

2.4

8 − 1

×

. A control study of the same bipyridyl base with ZnTPP
(TPP, tetraphenylporphyrin) showed no measurable change in
luminescence intensity of ZnTPP.

10 M

N

N

Zn Re(CO) 3 Cl

Cl(OC) 3 Re N N

N

N

N

N

N

N N N

45

Zn Zn

N N N N

N

N

N N

Cl(OC) 3 Re N Zn

N Re(CO) 3 Cl

N N

reported the flexible nature of a porphyrin moiety in the
rectangular assembly

Hupp et al.

5m [48]. Single-crystal structure of 5m showed