Photophysics and Photochemistry of Molecular Recognition and Sensing with Metal-Directed Macrocyclic Systems - Molecular Self-Assembly: Advances and Applications - page 307

long lifetime and large Stokes shift, the emission was attributed
to predominantly originating from triplet charge-transfer state(s).
The visible region spectra of molecular rectangles are

dominated by phorphyrin-based B- and Q-bands. In particular, the
Q-bands for both molecular assemblies are bathochromically shifted
ca. 20 and 10 nm to that of porphyrin bridge, respectively [48]. This
red shifting is consistent with electron-withdrawing effects due to
metal

4m and 5m

−

cation coordination. Both rectangular metallacycles 4m and

5m show red-shifted singlet emission maxima compared to the

porphyrin bridging complex at ca. 694 and 714 nm, respectively.
Interestingly, the emission from the rectangle 5m occurs from a

− 1

singlet state, which is ca. 3000 cm higher in energy than the usual

MLCT emission of Re

I

(diimine)(CO) complexes.

3

CO CO CO

CO O CO CO

Br Cl

OC CO OC OC

OC Re L Re C O OC Re L Re CO

OC Re Re CO

R

N N N CO N Br N CO N Cl

1

2 3

O

OC N N OC N N

N N Br Cl

OC R e Re CO OC Re L Re CO OC Re L Re CO

Br Cl

CO

OC R CO CO

CO CO

CO CO CO

CO

OC OC

CO CO

CO

OC OC

CO
CO

CO

OC Re L Re OC Re Re

L

N N N N N N

N N

N N

N N N N N N

Re L Re CO

OC OC Re L Re CO

OC CO

CO

OC CO

CO OC

OC

5

4

N N N N N N N N

c

b d

a

N

N

N

N N

N

N N

g

e

f

Cl

Cl

C 6 H 13

N N

N

N Zn

N

N

N N

C 6 H 13

OR OR

m

Br idging ligands(L)

h

The luminescent heterometallasquare (Re/Pd) 6 showed

3

∼

625 nm and
an emission lifetime of 17 ns in deoxygenated acetone [49]. The

emission from the MLCT state with a maximum at