only monomer emission and its allied CPL remain, while excimer fluorescence and
CPL are quenched in all cases. ECD spectra instead showed an exciton couplet
structures in the visible range, which is slightly blue-shifted upon cation addition.
12.3.2 Excimer CPL from Perylene Bisimide-Based Systems
Kawai’s group reported 1,2-diaminocyclohexane-based molecules linked to two
perylene bisimide moieties through a glycine linker (pery-5) or a β-alanine spacer
(pery-6, Scheme 12.9) [32]. A clear odd–even effect depending on the length of
linker is visible in the ECD profile which shows exciton couplets featuring
different signs in the two cases. In the case of pery-5, in CHCl 3 as the solvent
(C ¼ 10
À5 M), CPL profile showed a single band around 540 nm with the same
sign as the first Cotton effect in the ECD spectrum with similar g lum and g abs
values (g lum ~ |6 Â 10
À4 | and g abs ~ |4 Â 10
À4 |). This indicates that such
contribution stems from the weakly coupled lowest excitonic state. Compound
pery-6 showed the same CPL band. However, it displayed in addition an intense
and broad band with opposite sign around 630 nm originated from the excimer
state. As expected, this band displayed a much higher g lum (|8 Â 10
À3 |) than that
associated to the excitonic state emission.
On the contrary, when perylene bisimide moieties were mounted directly on a
binaphthyl scaffold (pery-7, Scheme 12.10) [33], only an emission from the lowest
excitonic state was observed in toluene, associated with a g lum value of |2 Â 10
À3
|–
|3 Â 10
À3 | around 550 nm. No significant contribution from the excimer was
visible, indicating that such structure does not allow for sufficient conformational
freedom to obtain an effective overlap between the two fluorophores.
O
O
O
O
O
O
O
O
O
H
H
HN
NH
O
O
O
O
O
O
HN
NH
O
O
O
O
O
O
HN
NH
pery-2
pery-3
pery-4
Lacour 2018
Scheme 12.8 Structures of perylene-functionalized macrocycles
12 Circularly Polarized Luminescence from Intramolecular Excimers
287
CPL are quenched in all cases. ECD spectra instead showed an exciton couplet
structures in the visible range, which is slightly blue-shifted upon cation addition.
12.3.2 Excimer CPL from Perylene Bisimide-Based Systems
Kawai’s group reported 1,2-diaminocyclohexane-based molecules linked to two
perylene bisimide moieties through a glycine linker (pery-5) or a β-alanine spacer
(pery-6, Scheme 12.9) [32]. A clear odd–even effect depending on the length of
linker is visible in the ECD profile which shows exciton couplets featuring
different signs in the two cases. In the case of pery-5, in CHCl 3 as the solvent
(C ¼ 10
À5 M), CPL profile showed a single band around 540 nm with the same
sign as the first Cotton effect in the ECD spectrum with similar g lum and g abs
values (g lum ~ |6 Â 10
À4 | and g abs ~ |4 Â 10
À4 |). This indicates that such
contribution stems from the weakly coupled lowest excitonic state. Compound
pery-6 showed the same CPL band. However, it displayed in addition an intense
and broad band with opposite sign around 630 nm originated from the excimer
state. As expected, this band displayed a much higher g lum (|8 Â 10
À3 |) than that
associated to the excitonic state emission.
On the contrary, when perylene bisimide moieties were mounted directly on a
binaphthyl scaffold (pery-7, Scheme 12.10) [33], only an emission from the lowest
excitonic state was observed in toluene, associated with a g lum value of |2 Â 10
À3
|–
|3 Â 10
À3 | around 550 nm. No significant contribution from the excimer was
visible, indicating that such structure does not allow for sufficient conformational
freedom to obtain an effective overlap between the two fluorophores.
O
O
O
O
O
O
O
O
O
H
H
HN
NH
O
O
O
O
O
O
HN
NH
O
O
O
O
O
O
HN
NH
pery-2
pery-3
pery-4
Lacour 2018
Scheme 12.8 Structures of perylene-functionalized macrocycles
12 Circularly Polarized Luminescence from Intramolecular Excimers
287