was observed for magadiite and dodecyltrimethylammonium (C 12 TMA)-exchanged
magadiite [201]. Because, in magadiite, the absorption shift was smaller and the
Stokes shift was larger than those of J-aggregate observed in other clays, PIC formed
aggregates in magadiite, while they were not the H- and the J-aggregates.
The H- and the J-aggregates of PIC were switched by swelling of host SA
[204]. A SA film with 46.4 meq/100 g (70%CEC) of PIC had absorption of the
monomer and a shoulder of the H-aggregate. By adding DMSO, the absorption of
the J-aggregate increased, and the monomer and the H-aggregate decreased. The
absorption spectrum returned to the initial shape by removing DMSO by washing
with ethanol and subsequently drying.
Aggregation of rhodamine 6G (R6G, Scheme 2) in the films of Wyoming
montmorillonites [176, 205] and laponites [172, 174–176] was investigated. R6G
had absorption at 527 nm in an aqueous solution, [172] and, by adding the montmorillonite, absorption at 534 nm due to J-aggregate and two shoulders at around
500 and 470 nm appeared [205]. The absorption at 500 nm increased, and the shift of
the monomer absorption from 527 to 538 nm was observed in a laponite film, which
corresponded to the formation of the H- and the J-aggregates [172]. H- and
J-aggregates were observed in the absorption and emission spectra of the film of a
hexadecyltrimethylammonium (C 16 TMA) exchanged KF [206]. Effective
quenching of the emission from the H-aggregate [207] was observed for auramine
O in SYn-1 powder [63], PIC in LP-RD powder [196], and merocyanine 540 in a
bentonite (obtained from Ordu/Ünye in Turkey) and the bentonite exchanged with
C 16 TMA [208].
4.2 Changes in the Photoluminescence Properties
4.2.1 Effects of the Host-Guest Interactions
Adsorption on the external surface and in the interlayer space of layered materials
suppresses molecular motion of dyes and induces a planar conformation [183, 209–
217]. Three different effects of electrostatic interactions and the suppression of the
molecular motion on the emission spectra have been proposed: (1) the bathochromic
shift of emission by electrostatic interactions, (2) smaller Stokes shift than that in
solutions owing to the similar molecular conformation of the excited and ground
states inducing hypsochromic shift and increase intensity of the hypsochromic
emission, or (3) decrease of the internal conversion rate due to the fixation of the
molecular conformation in the excited state on the external surface. These effects
were reported for porphyrins [17, 218–222], auramine O [223], and
triphenylbenzene derivatives [224].
Porphyrins have two π-π
à transitions known as Soret band at around 400–500 nm
and Q-band at around 500–700 nm. The Soret band and the Q-band of
tetraphenylporphine (TPP, Scheme 5) and Fe(III)-TPP shifted by the adsorption on
a purified Wyoming bentonite from 416 to 445 nm and 620 to 664 nm, respectively
[218]. The shift of the absorption was explained by the coplanar structure of the
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T. Yamaguchi et al.
magadiite [201]. Because, in magadiite, the absorption shift was smaller and the
Stokes shift was larger than those of J-aggregate observed in other clays, PIC formed
aggregates in magadiite, while they were not the H- and the J-aggregates.
The H- and the J-aggregates of PIC were switched by swelling of host SA
[204]. A SA film with 46.4 meq/100 g (70%CEC) of PIC had absorption of the
monomer and a shoulder of the H-aggregate. By adding DMSO, the absorption of
the J-aggregate increased, and the monomer and the H-aggregate decreased. The
absorption spectrum returned to the initial shape by removing DMSO by washing
with ethanol and subsequently drying.
Aggregation of rhodamine 6G (R6G, Scheme 2) in the films of Wyoming
montmorillonites [176, 205] and laponites [172, 174–176] was investigated. R6G
had absorption at 527 nm in an aqueous solution, [172] and, by adding the montmorillonite, absorption at 534 nm due to J-aggregate and two shoulders at around
500 and 470 nm appeared [205]. The absorption at 500 nm increased, and the shift of
the monomer absorption from 527 to 538 nm was observed in a laponite film, which
corresponded to the formation of the H- and the J-aggregates [172]. H- and
J-aggregates were observed in the absorption and emission spectra of the film of a
hexadecyltrimethylammonium (C 16 TMA) exchanged KF [206]. Effective
quenching of the emission from the H-aggregate [207] was observed for auramine
O in SYn-1 powder [63], PIC in LP-RD powder [196], and merocyanine 540 in a
bentonite (obtained from Ordu/Ünye in Turkey) and the bentonite exchanged with
C 16 TMA [208].
4.2 Changes in the Photoluminescence Properties
4.2.1 Effects of the Host-Guest Interactions
Adsorption on the external surface and in the interlayer space of layered materials
suppresses molecular motion of dyes and induces a planar conformation [183, 209–
217]. Three different effects of electrostatic interactions and the suppression of the
molecular motion on the emission spectra have been proposed: (1) the bathochromic
shift of emission by electrostatic interactions, (2) smaller Stokes shift than that in
solutions owing to the similar molecular conformation of the excited and ground
states inducing hypsochromic shift and increase intensity of the hypsochromic
emission, or (3) decrease of the internal conversion rate due to the fixation of the
molecular conformation in the excited state on the external surface. These effects
were reported for porphyrins [17, 218–222], auramine O [223], and
triphenylbenzene derivatives [224].
Porphyrins have two π-π
à transitions known as Soret band at around 400–500 nm
and Q-band at around 500–700 nm. The Soret band and the Q-band of
tetraphenylporphine (TPP, Scheme 5) and Fe(III)-TPP shifted by the adsorption on
a purified Wyoming bentonite from 416 to 445 nm and 620 to 664 nm, respectively
[218]. The shift of the absorption was explained by the coplanar structure of the
266
T. Yamaguchi et al.