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Albeit tris(8-hydroxyquinolinato) aluminum (Alq(3)) and its derivatives are prominent emitter materials for organic lighting devices, and the optical transitions occur among ligand-centered states, the use of metal-free 8-hydroxyquinoline is impractical as it suffers from strong nonradiative quenching, mainly through fast proton transfer. Herein, it is shown that the problem of rapid proton exchange and vibration quenching of light emission can be overcome not only by complexation, but also by organization of the 8-hydroxyquinolinium cations into a solid rigid network with appropriate counter-anions (here bis(trifluoromethanesulfonyl)imide). The resulting structure is stiffened by secondary bonding interactions such as pi-stacking and hydrogen bonds, which efficiently block rapid proton transfer quenching and reduce vibrational deactivation. Additionally, the optical properties are tuned through methyl substitution from deep blue (455 nm) to blue-green (488 nm). Time-dependent density functional theory (TDFT) calculations reveal the emission to occur from which an unexpectedly long-lived S-1 level, unusual for organic fluorophores. All compounds show comparable, even superior photoluminescence compared to Alq(3) and related materials, both as solids and thin films with quantum yields (QYs) up to 40-50%. In addition, all compounds show appreciable thermal stability with decomposition temperatures above 310 degrees C., Funding Agencies|Royal Academy of Science; Swedish Energy Agency [46676-1, 50779-1]; Swedish Research Council [2020-04600, 2021-0477]; Swedish Foundation for Strategic Research [EM16-0013]; SSF [2020-04437]; Swedish Research Council [2018-05973]

Albeit tris(8-hydroxyquinolinato) aluminum (Alq(3)) and its derivatives are prominent emitter materials for organic lighting devices, and the optical transitions occur among ligand-centered states, the use of metal-free 8-hydroxyquinoline is impractical as it suffers from strong nonradiative quenching, mainly through fast proton transfer. Herein, it is shown that the problem of rapid proton exchange and vibration quenching of light emission can be overcome not only by complexation, but also by organization of the 8-hydroxyquinolinium cations into a solid rigid network with appropriate counter-anions (here bis(trifluoromethanesulfonyl)imide). The resulting structure is stiffened by secondary bonding interactions such as pi-stacking and hydrogen bonds, which efficiently block rapid proton transfer quenching and reduce vibrational deactivation. Additionally, the optical properties are tuned through methyl substitution from deep blue (455 nm) to blue-green (488 nm). Time-dependent density functional theory (TDFT) calculations reveal the emission to occur from which an unexpectedly long-lived S-1 level, unusual for organic fluorophores. All compounds show comparable, even superior photoluminescence compared to Alq(3) and related materials, both as solids and thin films with quantum yields (QYs) up to 40-50%. In addition, all compounds show appreciable thermal stability with decomposition temperatures above 310 degrees C., Funding Agencies|Royal Academy of Science; Swedish Energy Agency [46676-1, 50779-1]; Swedish Research Council [2020-04600, 2021-0477]; Swedish Foundation for Strategic Research [EM16-0013]; SSF [2020-04437]; Swedish Research Council [2018-05973]

Albeit tris(8-hydroxyquinolinato) aluminum (Alq(3)) and its derivatives are prominent emitter materials for organic lighting devices, and the optical transitions occur among ligand-centered states, the use of metal-free 8-hydroxyquinoline is impractical as it suffers from strong nonradiative quenching, mainly through fast proton transfer. Herein, it is shown that the problem of rapid proton exchange and vibration quenching of light emission can be overcome not only by complexation, but also by organization of the 8-hydroxyquinolinium cations into a solid rigid network with appropriate counter-anions (here bis(trifluoromethanesulfonyl)imide). The resulting structure is stiffened by secondary bonding interactions such as pi-stacking and hydrogen bonds, which efficiently block rapid proton transfer quenching and reduce vibrational deactivation. Additionally, the optical properties are tuned through methyl substitution from deep blue (455 nm) to blue-green (488 nm). Time-dependent density functional theory (TDFT) calculations reveal the emission to occur from which an unexpectedly long-lived S-1 level, unusual for organic fluorophores. All compounds show comparable, even superior photoluminescence compared to Alq(3) and related materials, both as solids and thin films with quantum yields (QYs) up to 40-50%. In addition, all compounds show appreciable thermal stability with decomposition temperatures above 310 degrees C., Funding Agencies|Royal Academy of Science; Swedish Energy Agency [46676-1, 50779-1]; Swedish Research Council [2020-04600, 2021-0477]; Swedish Foundation for Strategic Research [EM16-0013]; SSF [2020-04437]; Swedish Research Council [2018-05973]

Albeit tris(8-hydroxyquinolinato) aluminum (Alq(3)) and its derivatives are prominent emitter materials for organic lighting devices, and the optical transitions occur among ligand-centered states, the use of metal-free 8-hydroxyquinoline is impractical as it suffers from strong nonradiative quenching, mainly through fast proton transfer. Herein, it is shown that the problem of rapid proton exchange and vibration quenching of light emission can be overcome not only by complexation, but also by organization of the 8-hydroxyquinolinium cations into a solid rigid network with appropriate counter-anions (here bis(trifluoromethanesulfonyl)imide). The resulting structure is stiffened by secondary bonding interactions such as pi-stacking and hydrogen bonds, which efficiently block rapid proton transfer quenching and reduce vibrational deactivation. Additionally, the optical properties are tuned through methyl substitution from deep blue (455 nm) to blue-green (488 nm). Time-dependent density functional theory (TDFT) calculations reveal the emission to occur from which an unexpectedly long-lived S-1 level, unusual for organic fluorophores. All compounds show comparable, even superior photoluminescence compared to Alq(3) and related materials, both as solids and thin films with quantum yields (QYs) up to 40-50%. In addition, all compounds show appreciable thermal stability with decomposition temperatures above 310 degrees C., Funding Agencies|Royal Academy of Science; Swedish Energy Agency [46676-1, 50779-1]; Swedish Research Council [2020-04600, 2021-0477]; Swedish Foundation for Strategic Research [EM16-0013]; SSF [2020-04437]; Swedish Research Council [2018-05973]

Albeit tris(8-hydroxyquinolinato) aluminum (Alq(3)) and its derivatives are prominent emitter materials for organic lighting devices, and the optical transitions occur among ligand-centered states, the use of metal-free 8-hydroxyquinoline is impractical as it suffers from strong nonradiative quenching, mainly through fast proton transfer. Herein, it is shown that the problem of rapid proton exchange and vibration quenching of light emission can be overcome not only by complexation, but also by organization of the 8-hydroxyquinolinium cations into a solid rigid network with appropriate counter-anions (here bis(trifluoromethanesulfonyl)imide). The resulting structure is stiffened by secondary bonding interactions such as pi-stacking and hydrogen bonds, which efficiently block rapid proton transfer quenching and reduce vibrational deactivation. Additionally, the optical properties are tuned through methyl substitution from deep blue (455 nm) to blue-green (488 nm). Time-dependent density functional theory (TDFT) calculations reveal the emission to occur from which an unexpectedly long-lived S-1 level, unusual for organic fluorophores. All compounds show comparable, even superior photoluminescence compared to Alq(3) and related materials, both as solids and thin films with quantum yields (QYs) up to 40-50%. In addition, all compounds show appreciable thermal stability with decomposition temperatures above 310 degrees C., Funding Agencies|Royal Academy of Science; Swedish Energy Agency [46676-1, 50779-1]; Swedish Research Council [2020-04600, 2021-0477]; Swedish Foundation for Strategic Research [EM16-0013]; SSF [2020-04437]; Swedish Research Council [2018-05973]

Many crystalline materials form polymorphs and undergo solid-solid transitions between different forms as a function of temperature or pressure. However, there is still a poor understanding of the mechanism of transformation. Conclusions about the transformation process are typically drawn by comparing the crystal structures before and after the conversion, but gaining detailed mechanistic knowledge is strongly impeded by the generally fast rate of these transitions. When the crystal morphology does not change, it is assumed that crystallinity is maintained throughout the process. Here we report transformation between polymorphs of ZnCl2(1,3-diethylimidazole-2-thione)(2) which are sufficiently slow to allow unambiguous assignment of single crystal to single crystal transformation with shape preservation proceeding through an amorphous intermediate phase. This result fundamentally challenges the commonly accepted views of polymorphic phase transition mechanisms., Funding Agencies|Novo Nordisk FoundationNovo Nordisk FoundationNovocure Limited; Knut and Alice Wallenberg FoundationKnut & Alice Wallenberg Foundation; Royal Academy of Sciences, Sweden; Swedish Research Council (Vetenskapsradet, VR)Swedish Research Council [2018-05973, 2020-05405, 2018-00233, 2020-04600, SNIC 2020-3-29]

Many crystalline materials form polymorphs and undergo solid-solid transitions between different forms as a function of temperature or pressure. However, there is still a poor understanding of the mechanism of transformation. Conclusions about the transformation process are typically drawn by comparing the crystal structures before and after the conversion, but gaining detailed mechanistic knowledge is strongly impeded by the generally fast rate of these transitions. When the crystal morphology does not change, it is assumed that crystallinity is maintained throughout the process. Here we report transformation between polymorphs of ZnCl2(1,3-diethylimidazole-2-thione)(2) which are sufficiently slow to allow unambiguous assignment of single crystal to single crystal transformation with shape preservation proceeding through an amorphous intermediate phase. This result fundamentally challenges the commonly accepted views of polymorphic phase transition mechanisms., Funding Agencies|Novo Nordisk FoundationNovo Nordisk FoundationNovocure Limited; Knut and Alice Wallenberg FoundationKnut & Alice Wallenberg Foundation; Royal Academy of Sciences, Sweden; Swedish Research Council (Vetenskapsradet, VR)Swedish Research Council [2018-05973, 2020-05405, 2018-00233, 2020-04600, SNIC 2020-3-29]

Many crystalline materials form polymorphs and undergo solid-solid transitions between different forms as a function of temperature or pressure. However, there is still a poor understanding of the mechanism of transformation. Conclusions about the transformation process are typically drawn by comparing the crystal structures before and after the conversion, but gaining detailed mechanistic knowledge is strongly impeded by the generally fast rate of these transitions. When the crystal morphology does not change, it is assumed that crystallinity is maintained throughout the process. Here we report transformation between polymorphs of ZnCl2(1,3-diethylimidazole-2-thione)(2) which are sufficiently slow to allow unambiguous assignment of single crystal to single crystal transformation with shape preservation proceeding through an amorphous intermediate phase. This result fundamentally challenges the commonly accepted views of polymorphic phase transition mechanisms., Funding Agencies|Novo Nordisk FoundationNovo Nordisk FoundationNovocure Limited; Knut and Alice Wallenberg FoundationKnut & Alice Wallenberg Foundation; Royal Academy of Sciences, Sweden; Swedish Research Council (Vetenskapsradet, VR)Swedish Research Council [2018-05973, 2020-05405, 2018-00233, 2020-04600, SNIC 2020-3-29]

Many crystalline materials form polymorphs and undergo solid-solid transitions between different forms as a function of temperature or pressure. However, there is still a poor understanding of the mechanism of transformation. Conclusions about the transformation process are typically drawn by comparing the crystal structures before and after the conversion, but gaining detailed mechanistic knowledge is strongly impeded by the generally fast rate of these transitions. When the crystal morphology does not change, it is assumed that crystallinity is maintained throughout the process. Here we report transformation between polymorphs of ZnCl2(1,3-diethylimidazole-2-thione)(2) which are sufficiently slow to allow unambiguous assignment of single crystal to single crystal transformation with shape preservation proceeding through an amorphous intermediate phase. This result fundamentally challenges the commonly accepted views of polymorphic phase transition mechanisms., Funding Agencies|Novo Nordisk FoundationNovo Nordisk FoundationNovocure Limited; Knut and Alice Wallenberg FoundationKnut & Alice Wallenberg Foundation; Royal Academy of Sciences, Sweden; Swedish Research Council (Vetenskapsradet, VR)Swedish Research Council [2018-05973, 2020-05405, 2018-00233, 2020-04600, SNIC 2020-3-29]

Many crystalline materials form polymorphs and undergo solid-solid transitions between different forms as a function of temperature or pressure. However, there is still a poor understanding of the mechanism of transformation. Conclusions about the transformation process are typically drawn by comparing the crystal structures before and after the conversion, but gaining detailed mechanistic knowledge is strongly impeded by the generally fast rate of these transitions. When the crystal morphology does not change, it is assumed that crystallinity is maintained throughout the process. Here we report transformation between polymorphs of ZnCl2(1,3-diethylimidazole-2-thione)(2) which are sufficiently slow to allow unambiguous assignment of single crystal to single crystal transformation with shape preservation proceeding through an amorphous intermediate phase. This result fundamentally challenges the commonly accepted views of polymorphic phase transition mechanisms., Funding Agencies|Novo Nordisk FoundationNovo Nordisk FoundationNovocure Limited; Knut and Alice Wallenberg FoundationKnut & Alice Wallenberg Foundation; Royal Academy of Sciences, Sweden; Swedish Research Council (Vetenskapsradet, VR)Swedish Research Council [2018-05973, 2020-05405, 2018-00233, 2020-04600, SNIC 2020-3-29]