Kawai’s group reported a tetrathiazole-based compound which undergoes ringopening/closure through a photoinduced reaction promoted by ultraviolet (UV) (for
ring closure) or visible (for ring opening) light (pyr-23, Scheme 12.5) [24]. This
transformation is accompanied by a large structural change. In the ring-open form,
the two pyrene moieties are in close proximity giving rise to excimer-associated CPL
with g lum around 10
À2 (C ¼ 1.7 Â 10
À4 M in CHCl 3 ). Upon photocyclization and
the rigidification of the core three-dimensional (3D) structure, the two pyrene units
are brought far apart, which results in a quenching of excimer CPL. Such light
promoted CPL switching can be repeated over several cycles.
A molecule displaying concentration dependent CPL was developed by Asami
and coworkers: [25] a dibenzofuran molecule linked to two pyrene moieties through
a chiral chain (pyr-24, Fig. 12.4). Such compound shows a bisignate CPL profile,
where monomer and excimer allied CPL have opposite signs (Fig. 12.4). Such sign
N
S
N
S
Ph
Ph
HN
HN
O
NH
R
O
N
S
N
S
O
NH
R
O
UV
Vis
pyr-23
Kawai 2016
N
S
N
Ph
N
S
Ph
S
HN
O
R
NH
S
HN
O
R
NH
O
N
O
Scheme 12.5 Tetrathiazole-based chiroptical switch reported by Kawai et al.
O
NH
HN
pyr-24
Asami 2017
(R,R)-pyr-24
(S,S)-pyr-24
Fig. 12.4 Concentration responsive pyrene-dibenzofuran molecule and CPL and total fluorescence
as a function of pyr-24 concentration in toluene. Adapted from reference [25] with permission from
The Royal Society of Chemistry
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F. Zinna et al.