Luminescence induced by crystallization of organic binary mixtures

Abstract

Publication costs assisted by Fuji Photo Film Co. Ltd.A novel series of crystalloluminescent organic materials is discovered. The binary mixture of a nonconjugated ketone and acetonitrile or AvY-dimethylacetamide emits blue-white light pulses on crystallization at 77°K. The experimental conditions for effective emission are described. The experimental facts suggest the excitation mechanism that the emission phenomenon is essentially triboluminescence, brought about by strain energy in the mixed crystal. The crystalloluminescence spectra were recorded photographically with the use of a continuous interference filter. The emission spectra, with the maximum at about 460 nm, are able to be replaced by different spectra by the addition of a small amount of appropriate sensitizers. The mechanism of the emission process is elucidated by comparing the crystalloluminescence spectrum with photoluminescence spectra. In the absence of sensitizers, the crystalloluminescence emission comes from the lowest excited triplet state of the nonconjugated ketones, while with doped sensitizers, the triplet energy transfer takes place from the ketone to the sensitizers, the triplet states of which are responsible for the observed emission.

Fluorescent Crystalloluminescence of N-Isopropylcarbazole

“…In related studies in the past, it was reported that XTL events sometimes accompanied emission from an impurity other than that from the XTL-active compound itself. , However, in the present experiments, no phosphorescence at all was detected from the NIPCz (λ max ∼ 500 nm) . It is worth noting, furthermore, that Takeda et al investigated XTL from a binary mixture (methylbutyl ketone/dimethylacetamide) doped with oxazole derivatives (POPOP, etc) as a fluorescence sensitizer . In this case, neither fluorescence nor phosphorescence was detected from the oxazole derivative in the XTL spectrum of the binary mixture.…”

“…16 It is worth noting, furthermore, that Takeda et al investigated XTL from a binary mixture (methylbutyl ketone/dimethylacetamide) doped with oxazole derivatives (POPOP, etc) as a fluorescence sensitizer. 9 In this case, neither fluorescence nor phosphorescence was detected from the oxazole derivative in the XTL spectrum of the binary mixture. Therefore, to the best of our knowledge, this is the first report of fluorescent crystalloluminescence from an organic compound: NIPCz.…”

“…Therefore, the mechanisms leading to XTL have hardly been discussed in terms of the thermodynamics of the crystallization process. It is worth noting, furthermore, that the excited states of the XTLactive compounds reported previously possess (n, π*) character, so the XTL spectra reported in the literature [8][9][10][11] are phosphorescent in origin rather than fluorescent. It is true that phosphoresce is much weaker in intensity than fluorescence and is likely to suffer from impurity and/or oxygen quenching.…”

“…The first example was demonstrated for benzanilide by Safonov et al in 1964, and the second was reported for binary solution mixtures (acetone/acetonitrile, etc.) by Takeda et al in 1973 . In 1982, Zink et al reported the XTL spectrum of methyl salicylate .…”

Crystalloluminescence produced during the polymorphic phase transition of growing crystallites

“…Only a limited number of organic and inorganic materials is known to be crystalloluminescent (Barsanti and Maccarrone 1991). The CRL emission may occur due to several processes such as (i) amorphous to crystalline transformation, (ii) polymorphic phase transition, (iii) microfracture of crystallites and (iv) chemical reaction during crystallization (Harvey 1957, Garten and Head 1963, 1966, 1970, Tsuda et al 1939, Walton 1977, Chandra and Zink 1980, Chandra 1982, Takeda et al 1973, Gibbon et al 1988, Barsanti and Maccarrone 1991.…”