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1,3,2,4-Diazadiboretidine, an isoelectronic heteroanalogue of cyclobutadiene, is an interesting chemical species in terms of comparison with the carbon system, whereas its properties have never been investigated experimentally. According to Baird's rule, Huckel antiaromatic cyclobutadiene acquires aromaticity in the lowest triplet state. Here we report experimental and theoretical studies on the ground- and excited-state antiaromaticity/aromaticity as well as the photophysical properties of an isolable 1,3,2,4-diazadiboretidine derivative. The crystal structure of the diazadiboretidine derivative revealed that the B2N2 ring adopts a planar rhombic geometry in the ground state. Yet, theoretical calculations showed that the B2N2 ring turns to a square geometry with a nonaromatic character in the lowest triplet state. Notably, the diazadiboretidine derivative has the lowest singlet and triplet states lying at close energy levels and displays blue phosphorescence.

The ground- and excited-state properties of a diazadiboretidine (DADBT) derivative, an isoelectronic heterocyclic analogue of cyclobutadiene, are reported by Henrik Ottosson, Hiromi Nakai, Tadaaki Ikoma, Takanori Fukushima, and co-workers in their Research Article on page 21817. While the B2N2 ring of the DADBT derivative adopts a rhombic geometry in the ground state, it turns to a square geometry with a nonaromatic character in the lowest triplet state. Notably, the DADBT derivative displays blue phosphorescence in solution, providing insight into the photophysical properties of heterocyclic pi-systems.+

The exact energies of the lowest singlet and triplet excited states in organic chromophores are crucial to their performance in optoelectronic devices. The possibility of utilizing singlet fission to enhance the performance of photovoltaic devices has resulted in a wide demand for tuneable, stable organic chromophores with wide S1–T1 energy gaps (>1 eV). Cibalackrot-type compounds were recently considered to have favorably positioned excited state energies for singlet fission, and they were found to have a degree of aromaticity in the lowest triplet excited state (T1). This work reports on a revised and deepened theoretical analysis taking into account the excited state Hückel-aromatic (instead of Baird-aromatic) as well as diradical characters, with the aim to design new organic chromophores based on this scaffold in a rational way starting from qualitative theory. We demonstrate that the substituent strategy can effectively adjust the spin distribution on the chromophore and thereby manipulate the excited state energy levels. Additionally, the improved understanding of the aromatic characters enables us to demonstrate a feasible design strategy to vary the excited state energy levels by tuning the number and nature of Hückel-aromatic units in the excited state. Finally, our study elucidates the complications and pitfalls of the excited state aromaticity and antiaromaticity concepts, highlighting that quantitative results from quantum chemical calculations of various aromaticity indices must be linked with qualitative theoretical analysis of the character of the excited states.

The exact energies of the lowest singlet and triplet excited states in organic chromophores are crucial to their performance in optoelectronic devices. The possibility of utilizing singlet fission to enhance the performance of photovoltaic devices has resulted in a wide demand for tuneable, stable organic chromophores with wide S1–T1 energy gaps (>1 eV). Cibalackrot-type compounds were recently considered to have favorably positioned excited state energies for singlet fission, and they were found to have a degree of aromaticity in the lowest triplet excited state (T1). This work reports on a revised and deepened theoretical analysis taking into account the excited state Hückel-aromatic (instead of Baird-aromatic) as well as diradical characters, with the aim to design new organic chromophores based on this scaffold in a rational way starting from qualitative theory. We demonstrate that the substituent strategy can effectively adjust the spin distribution on the chromophore and thereby manipulate the excited state energy levels. Additionally, the improved understanding of the aromatic characters enables us to demonstrate a feasible design strategy to vary the excited state energy levels by tuning the number and nature of Hückel-aromatic units in the excited state. Finally, our study elucidates the complications and pitfalls of the excited state aromaticity and antiaromaticity concepts, highlighting that quantitative results from quantum chemical calculations of various aromaticity indices must be linked with qualitative theoretical analysis of the character of the excited states.

The exact energies of the lowest singlet and triplet excited states in organic chromophores are crucial to their performance in optoelectronic devices. The possibility of utilizing singlet fission to enhance the performance of photovoltaic devices has resulted in a wide demand for tuneable, stable organic chromophores with wide S1–T1 energy gaps (>1 eV). Cibalackrot-type compounds were recently considered to have favorably positioned excited state energies for singlet fission, and they were found to have a degree of aromaticity in the lowest triplet excited state (T1). This work reports on a revised and deepened theoretical analysis taking into account the excited state Hückel-aromatic (instead of Baird-aromatic) as well as diradical characters, with the aim to design new organic chromophores based on this scaffold in a rational way starting from qualitative theory. We demonstrate that the substituent strategy can effectively adjust the spin distribution on the chromophore and thereby manipulate the excited state energy levels. Additionally, the improved understanding of the aromatic characters enables us to demonstrate a feasible design strategy to vary the excited state energy levels by tuning the number and nature of Hückel-aromatic units in the excited state. Finally, our study elucidates the complications and pitfalls of the excited state aromaticity and antiaromaticity concepts, highlighting that quantitative results from quantum chemical calculations of various aromaticity indices must be linked with qualitative theoretical analysis of the character of the excited states.

The aromaticity of cyclic 4n pi-electron molecules in their first pi pi* triplet state (T-1), labeled Baird aromaticity, has gained growing attention in the past decade. Here we explore computationally the limitations of T-1 state Baird aromaticity in macrocyclic compounds, [n]CM's, which are cyclic oligomers of four different monocycles (M = p-phenylene (PP), 2,5-linked furan (FU), 1,4-linked cyclohexa-1,3-diene (CHD), and 1,4-linked cyclopentadiene (CPD)). We strive for conclusions that are general for various DFT functionals, although for macrocycles with up to 20 pi-electrons in their main conjugation paths we find that for their T-1 states single-point energies at both canonical UCCSD(T) and approximative DLPNO-UCCSD(T) levels are lowest when based on UB3LYP over UM06-2X and UCAM-B3LYP geometries. This finding is in contrast to what has earlier been observed for the electronic ground state of expanded porphyrins. Yet, irrespective of functional, macrocycles with 2,5-linked furans ([n]CFU's) retain Baird aromaticity until larger n than those composed of the other three monocycles. Also, when based on geometric, electronic and energetic aspects of aromaticity, a (3)[n]CFU with a specific n is more strongly Baird-aromatic than the analogous (3)[n]CPP while the magnetic indices tell the opposite. To construct large T-1 state Baird-aromatic [n]CM's, the design should be such that the T-1 state Baird aromaticity of the macrocyclic perimeter dominates over a situation with local closed-shell Hiickel aromaticity of one or a few monocycles and semilocalized triplet diradical character. Monomers with lower Hiickel aromaticity in S-0 than benzene (e.g., furan) that do not impose steric congestion are preferred. Structural confinement imposed by, e.g., methylene bridges is also an approach to larger Baird-aromatic macrocycles. Finally, by using the Zilberg-Haas description of T-1 state aromaticity, we reveal the analogy to the Bickel aromaticity of the corresponding closed

The aromaticity of cyclic 4n pi-electron molecules in their first pi pi* triplet state (T-1), labeled Baird aromaticity, has gained growing attention in the past decade. Here we explore computationally the limitations of T-1 state Baird aromaticity in macrocyclic compounds, [n]CM's, which are cyclic oligomers of four different monocycles (M = p-phenylene (PP), 2,5-linked furan (FU), 1,4-linked cyclohexa-1,3-diene (CHD), and 1,4-linked cyclopentadiene (CPD)). We strive for conclusions that are general for various DFT functionals, although for macrocycles with up to 20 pi-electrons in their main conjugation paths we find that for their T-1 states single-point energies at both canonical UCCSD(T) and approximative DLPNO-UCCSD(T) levels are lowest when based on UB3LYP over UM06-2X and UCAM-B3LYP geometries. This finding is in contrast to what has earlier been observed for the electronic ground state of expanded porphyrins. Yet, irrespective of functional, macrocycles with 2,5-linked furans ([n]CFU's) retain Baird aromaticity until larger n than those composed of the other three monocycles. Also, when based on geometric, electronic and energetic aspects of aromaticity, a (3)[n]CFU with a specific n is more strongly Baird-aromatic than the analogous (3)[n]CPP while the magnetic indices tell the opposite. To construct large T-1 state Baird-aromatic [n]CM's, the design should be such that the T-1 state Baird aromaticity of the macrocyclic perimeter dominates over a situation with local closed-shell Hiickel aromaticity of one or a few monocycles and semilocalized triplet diradical character. Monomers with lower Hiickel aromaticity in S-0 than benzene (e.g., furan) that do not impose steric congestion are preferred. Structural confinement imposed by, e.g., methylene bridges is also an approach to larger Baird-aromatic macrocycles. Finally, by using the Zilberg-Haas description of T-1 state aromaticity, we reveal the analogy to the Bickel aromaticity of the corresponding closed

The aromaticity of cyclic 4n pi-electron molecules in their first pi pi* triplet state (T-1), labeled Baird aromaticity, has gained growing attention in the past decade. Here we explore computationally the limitations of T-1 state Baird aromaticity in macrocyclic compounds, [n]CM's, which are cyclic oligomers of four different monocycles (M = p-phenylene (PP), 2,5-linked furan (FU), 1,4-linked cyclohexa-1,3-diene (CHD), and 1,4-linked cyclopentadiene (CPD)). We strive for conclusions that are general for various DFT functionals, although for macrocycles with up to 20 pi-electrons in their main conjugation paths we find that for their T-1 states single-point energies at both canonical UCCSD(T) and approximative DLPNO-UCCSD(T) levels are lowest when based on UB3LYP over UM06-2X and UCAM-B3LYP geometries. This finding is in contrast to what has earlier been observed for the electronic ground state of expanded porphyrins. Yet, irrespective of functional, macrocycles with 2,5-linked furans ([n]CFU's) retain Baird aromaticity until larger n than those composed of the other three monocycles. Also, when based on geometric, electronic and energetic aspects of aromaticity, a (3)[n]CFU with a specific n is more strongly Baird-aromatic than the analogous (3)[n]CPP while the magnetic indices tell the opposite. To construct large T-1 state Baird-aromatic [n]CM's, the design should be such that the T-1 state Baird aromaticity of the macrocyclic perimeter dominates over a situation with local closed-shell Hiickel aromaticity of one or a few monocycles and semilocalized triplet diradical character. Monomers with lower Hiickel aromaticity in S-0 than benzene (e.g., furan) that do not impose steric congestion are preferred. Structural confinement imposed by, e.g., methylene bridges is also an approach to larger Baird-aromatic macrocycles. Finally, by using the Zilberg-Haas description of T-1 state aromaticity, we reveal the analogy to the Bickel aromaticity of the corresponding closed

The exact energies of the lowest singlet and triplet excited states in organic chromophores are crucial to their performance in optoelectronic devices. The possibility of utilizing singlet fission to enhance the performance of photovoltaic devices has resulted in a wide demand for tuneable, stable organic chromophores with wide S1–T1 energy gaps (>1 eV). Cibalackrot-type compounds were recently considered to have favorably positioned excited state energies for singlet fission, and they were found to have a degree of aromaticity in the lowest triplet excited state (T1). This work reports on a revised and deepened theoretical analysis taking into account the excited state Hückel-aromatic (instead of Baird-aromatic) as well as diradical characters, with the aim to design new organic chromophores based on this scaffold in a rational way starting from qualitative theory. We demonstrate that the substituent strategy can effectively adjust the spin distribution on the chromophore and thereby manipulate the excited state energy levels. Additionally, the improved understanding of the aromatic characters enables us to demonstrate a feasible design strategy to vary the excited state energy levels by tuning the number and nature of Hückel-aromatic units in the excited state. Finally, our study elucidates the complications and pitfalls of the excited state aromaticity and antiaromaticity concepts, highlighting that quantitative results from quantum chemical calculations of various aromaticity indices must be linked with qualitative theoretical analysis of the character of the excited states.

The aromaticity of cyclic 4n pi-electron molecules in their first pi pi* triplet state (T-1), labeled Baird aromaticity, has gained growing attention in the past decade. Here we explore computationally the limitations of T-1 state Baird aromaticity in macrocyclic compounds, [n]CM's, which are cyclic oligomers of four different monocycles (M = p-phenylene (PP), 2,5-linked furan (FU), 1,4-linked cyclohexa-1,3-diene (CHD), and 1,4-linked cyclopentadiene (CPD)). We strive for conclusions that are general for various DFT functionals, although for macrocycles with up to 20 pi-electrons in their main conjugation paths we find that for their T-1 states single-point energies at both canonical UCCSD(T) and approximative DLPNO-UCCSD(T) levels are lowest when based on UB3LYP over UM06-2X and UCAM-B3LYP geometries. This finding is in contrast to what has earlier been observed for the electronic ground state of expanded porphyrins. Yet, irrespective of functional, macrocycles with 2,5-linked furans ([n]CFU's) retain Baird aromaticity until larger n than those composed of the other three monocycles. Also, when based on geometric, electronic and energetic aspects of aromaticity, a (3)[n]CFU with a specific n is more strongly Baird-aromatic than the analogous (3)[n]CPP while the magnetic indices tell the opposite. To construct large T-1 state Baird-aromatic [n]CM's, the design should be such that the T-1 state Baird aromaticity of the macrocyclic perimeter dominates over a situation with local closed-shell Hiickel aromaticity of one or a few monocycles and semilocalized triplet diradical character. Monomers with lower Hiickel aromaticity in S-0 than benzene (e.g., furan) that do not impose steric congestion are preferred. Structural confinement imposed by, e.g., methylene bridges is also an approach to larger Baird-aromatic macrocycles. Finally, by using the Zilberg-Haas description of T-1 state aromaticity, we reveal the analogy to the Bickel aromaticity of the corresponding closed

The exact energies of the lowest singlet and triplet excited states in organic chromophores are crucial to their performance in optoelectronic devices. The possibility of utilizing singlet fission to enhance the performance of photovoltaic devices has resulted in a wide demand for tuneable, stable organic chromophores with wide S1–T1 energy gaps (>1 eV). Cibalackrot-type compounds were recently considered to have favorably positioned excited state energies for singlet fission, and they were found to have a degree of aromaticity in the lowest triplet excited state (T1). This work reports on a revised and deepened theoretical analysis taking into account the excited state Hückel-aromatic (instead of Baird-aromatic) as well as diradical characters, with the aim to design new organic chromophores based on this scaffold in a rational way starting from qualitative theory. We demonstrate that the substituent strategy can effectively adjust the spin distribution on the chromophore and thereby manipulate the excited state energy levels. Additionally, the improved understanding of the aromatic characters enables us to demonstrate a feasible design strategy to vary the excited state energy levels by tuning the number and nature of Hückel-aromatic units in the excited state. Finally, our study elucidates the complications and pitfalls of the excited state aromaticity and antiaromaticity concepts, highlighting that quantitative results from quantum chemical calculations of various aromaticity indices must be linked with qualitative theoretical analysis of the character of the excited states.

The aromaticity of cyclic 4n pi-electron molecules in their first pi pi* triplet state (T-1), labeled Baird aromaticity, has gained growing attention in the past decade. Here we explore computationally the limitations of T-1 state Baird aromaticity in macrocyclic compounds, [n]CM's, which are cyclic oligomers of four different monocycles (M = p-phenylene (PP), 2,5-linked furan (FU), 1,4-linked cyclohexa-1,3-diene (CHD), and 1,4-linked cyclopentadiene (CPD)). We strive for conclusions that are general for various DFT functionals, although for macrocycles with up to 20 pi-electrons in their main conjugation paths we find that for their T-1 states single-point energies at both canonical UCCSD(T) and approximative DLPNO-UCCSD(T) levels are lowest when based on UB3LYP over UM06-2X and UCAM-B3LYP geometries. This finding is in contrast to what has earlier been observed for the electronic ground state of expanded porphyrins. Yet, irrespective of functional, macrocycles with 2,5-linked furans ([n]CFU's) retain Baird aromaticity until larger n than those composed of the other three monocycles. Also, when based on geometric, electronic and energetic aspects of aromaticity, a (3)[n]CFU with a specific n is more strongly Baird-aromatic than the analogous (3)[n]CPP while the magnetic indices tell the opposite. To construct large T-1 state Baird-aromatic [n]CM's, the design should be such that the T-1 state Baird aromaticity of the macrocyclic perimeter dominates over a situation with local closed-shell Hiickel aromaticity of one or a few monocycles and semilocalized triplet diradical character. Monomers with lower Hiickel aromaticity in S-0 than benzene (e.g., furan) that do not impose steric congestion are preferred. Structural confinement imposed by, e.g., methylene bridges is also an approach to larger Baird-aromatic macrocycles. Finally, by using the Zilberg-Haas description of T-1 state aromaticity, we reveal the analogy to the Bickel aromaticity of the corresponding closed

According to the currently accepted structure-property relationships, aceno-pentalenes with an angular shape (fused to the 1,2-bond of the acene) exhibit higher antiaromaticity than those with a linear shape (fused to the 2,3-bond of the acene). To explore and expand the current view, we designed and synthesized molecules where two isomeric, yet, different, 8 pi antiaromatic subunits, a benzocyclobutadiene (BCB) and a pentalene, are combined into, respectively, an angular and a linear topology via an unsaturated six-membered ring. The antiaromatic character of the molecules is supported experimentally by H-1 NMR, UV-vis, and cyclic voltammetry measurements and X-ray crystallography. The experimental results are further confirmed by theoretical studies including the calculation of several aromaticity indices (NICS, ACID, HOMA, FLU, MCI). In the case of the angular molecule, double bond-localization within the connecting six-membered ring resulted in reduced antiaromaticity of both the BCB and pentalene subunits, while the linear structure provided a competitive situation for the two unequal [4n]pi subunits. We found that in the latter case the BCB unit alleviated its unfavorable antiaromaticity more efficiently, leaving the pentalene with strong antiaromaticity. Thus, a reversed structure-antiaromaticity relationship when compared to aceno-pentalenes was achieved.

Bright, photostable, and nontoxic fluorescent contrast agents are critical for biological imaging. "Self-healing" dyes, in which triplet states are intramolecularly quenched, enable fluorescence imaging by increasing fluorophore brightness and longevity, while simultaneously reducing the generation of reactive oxygen species that promote phototoxicity. Here, we systematically examine the self-healing mechanism in cyanine-class organic fluorophores spanning the visible spectrum. We show that the Baird aromatic triplet-state energy of cyclooctatetraene can be physically altered to achieve order of magnitude enhancements in fluorophore brightness and signal-to-noise ratio in both the presence and absence of oxygen. We leverage these advances to achieve direct measurements of large-scale conformational dynamics within single molecules at submillisecond resolution using wide-field illumination and camera-based detection methods. These findings demonstrate the capacity to image functionally relevant conformational processes in biological systems in the kilohertz regime at physiological oxygen concentrations and shed important light on the multivariate parameters critical to self-healing organic fluorophore design.

Singlet exciton fission photovoltaic technology requires chromophores with their lowest excited states arranged so that 2E(T-1) < E(S-1) and E(S-1) < E(T-2). Herein, qualitative theory and quantum chemical calculations are used to develop explicit strategies on how to use Baird's 4n rule on excited-state aromaticity, combined with Huckel's 4n + 2 rule for ground-state aromaticity, to tailor new potential chromophores for singlet fission. We first analyze the E(T-1), E(S-1), and E(T-2) of benzene and cyclobutadiene (CBD) as excited-state antiaromatic and aromatic archetypes, respectively, and reveal that CBD fulfills the criteria on the state ordering for a singlet fission chromophore. We then look at fulvenes, a class of compounds that can be tuned by choice of substituents from Baird-antiaromatic to Baird-aromatic in T-1 and S-1 and from Huckel-aromatic to Huckel-antiaromatic in S-0. The T-1 and S-1 states of most substituted fulvenes (159 of 225) are described by singly excited HOMO -> LUMO configurations, providing a rational for the simultaneous tuning of E(T-1) and E(S-1) along an approximate (anti)aromaticity coordinate. Key to the tunability is the exchange integral (K-H,K-L), which ideally is constant throughout the compound class, providing a constant.E(S-1 - T-1). This leads us to a geometric model for the identification of singlet fission chromophores, and we explore what factors limit the model. Candidates with calculated E(T-1) values of similar to 1 eV or higher are identified among benzannelated 4npelectron compound classes and siloles. In brief, it is clarified how the joint utilization of Baird's 4n and Huckel's 4n + 2 rules, together with substituent effects (electronic and steric) and benzannelation, can be used to tailor new chromophores with potential use in singlet fission photovoltaics.

Bright, photostable, and nontoxic fluorescent contrast agents are critical for biological imaging. "Self-healing" dyes, in which triplet states are intramolecularly quenched, enable fluorescence imaging by increasing fluorophore brightness and longevity, while simultaneously reducing the generation of reactive oxygen species that promote phototoxicity. Here, we systematically examine the self-healing mechanism in cyanine-class organic fluorophores spanning the visible spectrum. We show that the Baird aromatic triplet-state energy of cyclooctatetraene can be physically altered to achieve order of magnitude enhancements in fluorophore brightness and signal-to-noise ratio in both the presence and absence of oxygen. We leverage these advances to achieve direct measurements of large-scale conformational dynamics within single molecules at submillisecond resolution using wide-field illumination and camera-based detection methods. These findings demonstrate the capacity to image functionally relevant conformational processes in biological systems in the kilohertz regime at physiological oxygen concentrations and shed important light on the multivariate parameters critical to self-healing organic fluorophore design.

Bright, photostable, and nontoxic fluorescent contrast agents are critical for biological imaging. "Self-healing" dyes, in which triplet states are intramolecularly quenched, enable fluorescence imaging by increasing fluorophore brightness and longevity, while simultaneously reducing the generation of reactive oxygen species that promote phototoxicity. Here, we systematically examine the self-healing mechanism in cyanine-class organic fluorophores spanning the visible spectrum. We show that the Baird aromatic triplet-state energy of cyclooctatetraene can be physically altered to achieve order of magnitude enhancements in fluorophore brightness and signal-to-noise ratio in both the presence and absence of oxygen. We leverage these advances to achieve direct measurements of large-scale conformational dynamics within single molecules at submillisecond resolution using wide-field illumination and camera-based detection methods. These findings demonstrate the capacity to image functionally relevant conformational processes in biological systems in the kilohertz regime at physiological oxygen concentrations and shed important light on the multivariate parameters critical to self-healing organic fluorophore design.

Singlet exciton fission photovoltaic technology requires chromophores with their lowest excited states arranged so that 2E(T-1) < E(S-1) and E(S-1) < E(T-2). Herein, qualitative theory and quantum chemical calculations are used to develop explicit strategies on how to use Baird's 4n rule on excited-state aromaticity, combined with Huckel's 4n + 2 rule for ground-state aromaticity, to tailor new potential chromophores for singlet fission. We first analyze the E(T-1), E(S-1), and E(T-2) of benzene and cyclobutadiene (CBD) as excited-state antiaromatic and aromatic archetypes, respectively, and reveal that CBD fulfills the criteria on the state ordering for a singlet fission chromophore. We then look at fulvenes, a class of compounds that can be tuned by choice of substituents from Baird-antiaromatic to Baird-aromatic in T-1 and S-1 and from Huckel-aromatic to Huckel-antiaromatic in S-0. The T-1 and S-1 states of most substituted fulvenes (159 of 225) are described by singly excited HOMO -> LUMO configurations, providing a rational for the simultaneous tuning of E(T-1) and E(S-1) along an approximate (anti)aromaticity coordinate. Key to the tunability is the exchange integral (K-H,K-L), which ideally is constant throughout the compound class, providing a constant.E(S-1 - T-1). This leads us to a geometric model for the identification of singlet fission chromophores, and we explore what factors limit the model. Candidates with calculated E(T-1) values of similar to 1 eV or higher are identified among benzannelated 4npelectron compound classes and siloles. In brief, it is clarified how the joint utilization of Baird's 4n and Huckel's 4n + 2 rules, together with substituent effects (electronic and steric) and benzannelation, can be used to tailor new chromophores with potential use in singlet fission photovoltaics.

Singlet exciton fission photovoltaic technology requires chromophores with their lowest excited states arranged so that 2E(T-1) < E(S-1) and E(S-1) < E(T-2). Herein, qualitative theory and quantum chemical calculations are used to develop explicit strategies on how to use Baird's 4n rule on excited-state aromaticity, combined with Huckel's 4n + 2 rule for ground-state aromaticity, to tailor new potential chromophores for singlet fission. We first analyze the E(T-1), E(S-1), and E(T-2) of benzene and cyclobutadiene (CBD) as excited-state antiaromatic and aromatic archetypes, respectively, and reveal that CBD fulfills the criteria on the state ordering for a singlet fission chromophore. We then look at fulvenes, a class of compounds that can be tuned by choice of substituents from Baird-antiaromatic to Baird-aromatic in T-1 and S-1 and from Huckel-aromatic to Huckel-antiaromatic in S-0. The T-1 and S-1 states of most substituted fulvenes (159 of 225) are described by singly excited HOMO -> LUMO configurations, providing a rational for the simultaneous tuning of E(T-1) and E(S-1) along an approximate (anti)aromaticity coordinate. Key to the tunability is the exchange integral (K-H,K-L), which ideally is constant throughout the compound class, providing a constant.E(S-1 - T-1). This leads us to a geometric model for the identification of singlet fission chromophores, and we explore what factors limit the model. Candidates with calculated E(T-1) values of similar to 1 eV or higher are identified among benzannelated 4npelectron compound classes and siloles. In brief, it is clarified how the joint utilization of Baird's 4n and Huckel's 4n + 2 rules, together with substituent effects (electronic and steric) and benzannelation, can be used to tailor new chromophores with potential use in singlet fission photovoltaics.

According to the currently accepted structure-property relationships, aceno-pentalenes with an angular shape (fused to the 1,2-bond of the acene) exhibit higher antiaromaticity than those with a linear shape (fused to the 2,3-bond of the acene). To explore and expand the current view, we designed and synthesized molecules where two isomeric, yet, different, 8 pi antiaromatic subunits, a benzocyclobutadiene (BCB) and a pentalene, are combined into, respectively, an angular and a linear topology via an unsaturated six-membered ring. The antiaromatic character of the molecules is supported experimentally by H-1 NMR, UV-vis, and cyclic voltammetry measurements and X-ray crystallography. The experimental results are further confirmed by theoretical studies including the calculation of several aromaticity indices (NICS, ACID, HOMA, FLU, MCI). In the case of the angular molecule, double bond-localization within the connecting six-membered ring resulted in reduced antiaromaticity of both the BCB and pentalene subunits, while the linear structure provided a competitive situation for the two unequal [4n]pi subunits. We found that in the latter case the BCB unit alleviated its unfavorable antiaromaticity more efficiently, leaving the pentalene with strong antiaromaticity. Thus, a reversed structure-antiaromaticity relationship when compared to aceno-pentalenes was achieved.

According to the currently accepted structure-property relationships, aceno-pentalenes with an angular shape (fused to the 1,2-bond of the acene) exhibit higher antiaromaticity than those with a linear shape (fused to the 2,3-bond of the acene). To explore and expand the current view, we designed and synthesized molecules where two isomeric, yet, different, 8 pi antiaromatic subunits, a benzocyclobutadiene (BCB) and a pentalene, are combined into, respectively, an angular and a linear topology via an unsaturated six-membered ring. The antiaromatic character of the molecules is supported experimentally by H-1 NMR, UV-vis, and cyclic voltammetry measurements and X-ray crystallography. The experimental results are further confirmed by theoretical studies including the calculation of several aromaticity indices (NICS, ACID, HOMA, FLU, MCI). In the case of the angular molecule, double bond-localization within the connecting six-membered ring resulted in reduced antiaromaticity of both the BCB and pentalene subunits, while the linear structure provided a competitive situation for the two unequal [4n]pi subunits. We found that in the latter case the BCB unit alleviated its unfavorable antiaromaticity more efficiently, leaving the pentalene with strong antiaromaticity. Thus, a reversed structure-antiaromaticity relationship when compared to aceno-pentalenes was achieved.

According to the currently accepted structure-property relationships, aceno-pentalenes with an angular shape (fused to the 1,2-bond of the acene) exhibit higher antiaromaticity than those with a linear shape (fused to the 2,3-bond of the acene). To explore and expand the current view, we designed and synthesized molecules where two isomeric, yet, different, 8 pi antiaromatic subunits, a benzocyclobutadiene (BCB) and a pentalene, are combined into, respectively, an angular and a linear topology via an unsaturated six-membered ring. The antiaromatic character of the molecules is supported experimentally by H-1 NMR, UV-vis, and cyclic voltammetry measurements and X-ray crystallography. The experimental results are further confirmed by theoretical studies including the calculation of several aromaticity indices (NICS, ACID, HOMA, FLU, MCI). In the case of the angular molecule, double bond-localization within the connecting six-membered ring resulted in reduced antiaromaticity of both the BCB and pentalene subunits, while the linear structure provided a competitive situation for the two unequal [4n]pi subunits. We found that in the latter case the BCB unit alleviated its unfavorable antiaromaticity more efficiently, leaving the pentalene with strong antiaromaticity. Thus, a reversed structure-antiaromaticity relationship when compared to aceno-pentalenes was achieved.

Bright, photostable, and nontoxic fluorescent contrast agents are critical for biological imaging. "Self-healing" dyes, in which triplet states are intramolecularly quenched, enable fluorescence imaging by increasing fluorophore brightness and longevity, while simultaneously reducing the generation of reactive oxygen species that promote phototoxicity. Here, we systematically examine the self-healing mechanism in cyanine-class organic fluorophores spanning the visible spectrum. We show that the Baird aromatic triplet-state energy of cyclooctatetraene can be physically altered to achieve order of magnitude enhancements in fluorophore brightness and signal-to-noise ratio in both the presence and absence of oxygen. We leverage these advances to achieve direct measurements of large-scale conformational dynamics within single molecules at submillisecond resolution using wide-field illumination and camera-based detection methods. These findings demonstrate the capacity to image functionally relevant conformational processes in biological systems in the kilohertz regime at physiological oxygen concentrations and shed important light on the multivariate parameters critical to self-healing organic fluorophore design.

Singlet exciton fission photovoltaic technology requires chromophores with their lowest excited states arranged so that 2E(T-1) < E(S-1) and E(S-1) < E(T-2). Herein, qualitative theory and quantum chemical calculations are used to develop explicit strategies on how to use Baird's 4n rule on excited-state aromaticity, combined with Huckel's 4n + 2 rule for ground-state aromaticity, to tailor new potential chromophores for singlet fission. We first analyze the E(T-1), E(S-1), and E(T-2) of benzene and cyclobutadiene (CBD) as excited-state antiaromatic and aromatic archetypes, respectively, and reveal that CBD fulfills the criteria on the state ordering for a singlet fission chromophore. We then look at fulvenes, a class of compounds that can be tuned by choice of substituents from Baird-antiaromatic to Baird-aromatic in T-1 and S-1 and from Huckel-aromatic to Huckel-antiaromatic in S-0. The T-1 and S-1 states of most substituted fulvenes (159 of 225) are described by singly excited HOMO -> LUMO configurations, providing a rational for the simultaneous tuning of E(T-1) and E(S-1) along an approximate (anti)aromaticity coordinate. Key to the tunability is the exchange integral (K-H,K-L), which ideally is constant throughout the compound class, providing a constant.E(S-1 - T-1). This leads us to a geometric model for the identification of singlet fission chromophores, and we explore what factors limit the model. Candidates with calculated E(T-1) values of similar to 1 eV or higher are identified among benzannelated 4npelectron compound classes and siloles. In brief, it is clarified how the joint utilization of Baird's 4n and Huckel's 4n + 2 rules, together with substituent effects (electronic and steric) and benzannelation, can be used to tailor new chromophores with potential use in singlet fission photovoltaics.

According to the currently accepted structure-property relationships, aceno-pentalenes with an angular shape (fused to the 1,2-bond of the acene) exhibit higher antiaromaticity than those with a linear shape (fused to the 2,3-bond of the acene). To explore and expand the current view, we designed and synthesized molecules where two isomeric, yet, different, 8 pi antiaromatic subunits, a benzocyclobutadiene (BCB) and a pentalene, are combined into, respectively, an angular and a linear topology via an unsaturated six-membered ring. The antiaromatic character of the molecules is supported experimentally by H-1 NMR, UV-vis, and cyclic voltammetry measurements and X-ray crystallography. The experimental results are further confirmed by theoretical studies including the calculation of several aromaticity indices (NICS, ACID, HOMA, FLU, MCI). In the case of the angular molecule, double bond-localization within the connecting six-membered ring resulted in reduced antiaromaticity of both the BCB and pentalene subunits, while the linear structure provided a competitive situation for the two unequal [4n]pi subunits. We found that in the latter case the BCB unit alleviated its unfavorable antiaromaticity more efficiently, leaving the pentalene with strong antiaromaticity. Thus, a reversed structure-antiaromaticity relationship when compared to aceno-pentalenes was achieved.

Bright, photostable, and nontoxic fluorescent contrast agents are critical for biological imaging. "Self-healing" dyes, in which triplet states are intramolecularly quenched, enable fluorescence imaging by increasing fluorophore brightness and longevity, while simultaneously reducing the generation of reactive oxygen species that promote phototoxicity. Here, we systematically examine the self-healing mechanism in cyanine-class organic fluorophores spanning the visible spectrum. We show that the Baird aromatic triplet-state energy of cyclooctatetraene can be physically altered to achieve order of magnitude enhancements in fluorophore brightness and signal-to-noise ratio in both the presence and absence of oxygen. We leverage these advances to achieve direct measurements of large-scale conformational dynamics within single molecules at submillisecond resolution using wide-field illumination and camera-based detection methods. These findings demonstrate the capacity to image functionally relevant conformational processes in biological systems in the kilohertz regime at physiological oxygen concentrations and shed important light on the multivariate parameters critical to self-healing organic fluorophore design.

Singlet exciton fission photovoltaic technology requires chromophores with their lowest excited states arranged so that 2E(T-1) < E(S-1) and E(S-1) < E(T-2). Herein, qualitative theory and quantum chemical calculations are used to develop explicit strategies on how to use Baird's 4n rule on excited-state aromaticity, combined with Huckel's 4n + 2 rule for ground-state aromaticity, to tailor new potential chromophores for singlet fission. We first analyze the E(T-1), E(S-1), and E(T-2) of benzene and cyclobutadiene (CBD) as excited-state antiaromatic and aromatic archetypes, respectively, and reveal that CBD fulfills the criteria on the state ordering for a singlet fission chromophore. We then look at fulvenes, a class of compounds that can be tuned by choice of substituents from Baird-antiaromatic to Baird-aromatic in T-1 and S-1 and from Huckel-aromatic to Huckel-antiaromatic in S-0. The T-1 and S-1 states of most substituted fulvenes (159 of 225) are described by singly excited HOMO -> LUMO configurations, providing a rational for the simultaneous tuning of E(T-1) and E(S-1) along an approximate (anti)aromaticity coordinate. Key to the tunability is the exchange integral (K-H,K-L), which ideally is constant throughout the compound class, providing a constant.E(S-1 - T-1). This leads us to a geometric model for the identification of singlet fission chromophores, and we explore what factors limit the model. Candidates with calculated E(T-1) values of similar to 1 eV or higher are identified among benzannelated 4npelectron compound classes and siloles. In brief, it is clarified how the joint utilization of Baird's 4n and Huckel's 4n + 2 rules, together with substituent effects (electronic and steric) and benzannelation, can be used to tailor new chromophores with potential use in singlet fission photovoltaics.

Due to the reversal in electron counts for aromaticity and antiaromaticity in the closed-shell singlet state (normally ground state, S-0) and lowest * triplet state (T-1 or T-0), as given by Huckel's and Baird's rules, respectively, fulvenes are influenced by their substituents in the opposite manner in the T-1 and S-0 states. This effect is caused by a reversal in the dipole moment when going from S-0 to T-1 as fulvenes adapt to the difference in electron counts for aromaticity in various states; they are aromatic chameleons. Thus, a substituent pattern that enhances (reduces) fulvene aromaticity in S-0 reduces (enhances) aromaticity in T-1, allowing for rationalizations of the triplet state energies (E-T) of substituted fulvenes. Through quantum chemical calculations, we now assess which substituents and which positions on the pentafulvene core are the most powerful for designing compounds with low or inverted E-T. As a means to increase the -electron withdrawing capacity of cyano groups, we found that protonation at the cyano N atoms of 6,6-dicyanopentafulvenes can be a route to on-demand formation of a fulvenium dication with a triplet ground state (T-0). The five-membered ring of this species is markedly Baird-aromatic, although less than the cyclopentadienyl cation known to have a Baird-aromatic T-0 state.

Compounds with dibenzannelated heterocycles with eight pi-electrons are found in a range of applications. These molecules often adopt a bent structure in the ground state (S-0) but can become planar in the first excited states (S-1 and T-1) because of the cyclically conjugated 4n pi central ring, which fulfils the requirements for excited state aromaticity. We report on a quantum chemical investigation of the aromatic character in the S-1 and T-1 states of dibenzannelated seven- and six-membered heterocycles with one, two, or three heteroatoms in the 8 pi-electron ring. These states could have pi pi* or n pi* character. We find that compounds with one or two heteroatoms in the central ring have pi pi* states as their S-1 and T-1 states. They are to a significant degree influenced by excited state aromaticity, and their optimal structures are planar or nearly planar. Among the heteroatoms, nitrogen provides for the strongest excited state aromaticity whereas oxygen provides for the weakest, following the established trend of the S-0 state. Yet, dibenzannelated seven-membered-ring compounds with N=N bonds have non-aromatic n pi* states with strongly puckered structures as their S-1 and T-1 states.

La presencia de mascotas en la sociedad cada vez está en crecimiento, en gran medida los perros. Este hecho implica tener un cuidado diario de tal mascota, con el fin de ofrecer las necesidades nutricionales. No todos los dueños pueden estar presente para ofrecer una dieta equilibrada a sus mascotas por muchos motivos. Este proyecto, entre otros, trata de dar una solución a dicho problema beneficiando tanto al dueño como a la mascota. El presente proyecto consiste en el diseño y fabricación de un sistema electrónico basado en IoT, con el fin de dispensar comida para mascotas de forma automática en determinadas horas programadas, que puede ser programado y monitorizado en tiempo real de forma local y remota. El usuario puede programar la fecha y hora real, personalizar el tiempo de dosificación y la cantidad según las necesidades de nutrición de la mascota. En este trabajo, se diseña un prototipo funcional para gatos, y perros de tamaño mediano y pequeño. Mediante la pantalla LCD y la APP el usuario puede interactuar y visualizar los diferentes parámetros del sistema como: la fecha, la hora, los horarios programados, los avisos etc. El software del sistema es implementado en un microcontrolador Arduino.

Electrides are ionic substances containing isolated electrons. These confined electrons are topologically characterised by a quasi-atom, that is, a non-nuclear attractor (NNA) of the electron density. The electronic structure of the octahedral 4 A1g Li6+ and 5 A1g Be6 species shows that these species have a large number of NNAs. These NNAs have highly delocalised electron densities and, as a result, the chemical bonding pattern of these systems is reminiscent of that in solid metals, in which metal cations are surrounded by a "sea" of delocalised valence electrons. We propose the term metal cluster electrides to refer to this new class of compounds. In this study, we establish a computational protocol to identify, characterize, and design metal cluster electrides and we elucidate the intricate bonding patterns of this particular type of species.

Developing norbornadiene-quadricyclane (NBD-QC) systems for molecular solar-thermal (MOST) energy storage is often a process of trial and error. By studying a series of norbornadienes (NBD-R-2) doubly substituted at the C7-position with R = H, Me, and iPr, we untangle the interrelated factors affecting MOST performance through a combination of experiment and theory. Increasing the steric bulk along the NBD-R-2 series gave higher quantum yields, slightly red-shifted absorptions, and longer thermal lifetimes of the energy-rich QC isomer. However, these advantages are counterbalanced by lower energy storage capacities, and overall R = Me appears most promising for short-term MOST applications. Computationally we find that it is the destabilization of the NBD isomer over the QC isomer with increasing steric bulk that is responsible for most of the observed trends and we can also predict the relative quantum yields by characterizing the S-1/S-0 conical intersections. The significantly increased thermal half-life of NBD-iPr(2) is caused by a higher activation entropy, highlighting a novel strategy to improve thermal half-lives of MOST compounds and other photo-switchable molecules without affecting their electronic properties. The potential of the NBD-R-2 compounds in devices is also explored, demonstrating a solar energy storage efficiency of up to 0.2%. Finally, we show how the insights gained in this study can be used to identify strategies to improve already existing NBD-QC systems.

Compounds that can be labeled as "aromatic chameleons" are pi-conjugated compounds that are able to adjust their pi-electron distributions so as to comply with the different rules of aromaticity in different electronic states. We used quantum chemical calculations to explore how the fusion of benzene rings onto aromatic chameleonic units represented by biphenylene, dibenbzocyclooctatetraene, and dibenzo[a,e]pentalene modifies the first triplet excited states (T-1) of the compounds. Decreases in T-1 energies are observed when going from isomers with linear connectivity of the fused benzene rings to those with cis- or transbent connectivities. The T-1 energies decreased down to those of the parent (isolated) 4n pi-electron units. Simultaneously, we observe an increased influence of triplet State aromaticity of the central 4n ring as given by Baird's rule and evidenced by geometric, magnetic, and electron density based aromaticity indices (HOMA, NICS-XY, ACID, and FLU). Because of an influence of,triplet state aromaticity in the central 4n pi-electron units,, the most stabilized, compounds, retain the triplet excitation in Baird pi-quartets or octets, enabling the outer benzene rings to adapt closed-shell singlet Clar pi-sextet character. Interestingly, the T-1 energies go down as the total number of aromatic cycles within a molecule in the T-1 state increases.

Les piridazinones són compostos orgànics que es troben en molts fàrmacs, en pesticides i en productes naturals amb activitat biològica. Fins al moment, s’ha publicat un nombre considerable de rutes sintètiques sobre l’obtenció de piridazinones, tot i que sols unes poques descriuen formes eficients de preparar piridazinones N-arilades. A diferència dels mètodes publicats a la bibliografia, en què se solen utilitzar condicions de reacció dràstiques o catalitzadors metàl·lics, el present treball proposa una nova ruta per a l’obtenció de piridazinones N-arilades mitjançant l’ús de sals d’arildiazoni i derivats de furan sota condicions de reacció suaus, incloent-hi l’aigua com a dissolvent. Les sals de diazoni són compostos de gran reactivitat, la qual cosa representa un avantatge important pel que fa a l’eficiència del procés. L’elucidació del mecanisme de la reacció s’ha dut a terme emprant càlculs DFT i s’ha confirmat amb la realització de proves empíriques.Paraules clau: Piridazinones N-arilades, sals d’arildiazoni, càlculs DFT., Pyridazinones are organic compounds that are commonly found in drugs, pesticides, and natural products with biological activity. To date, a considerable number of synthetic routes to obtain pyridazinones have been published although only a few have described efficient pathways to prepare N-arylated pyridazinones. In contrast to methods found in literature in which strong reaction conditions or metallic catalysts are employed, this study proposes a new route to obtain N-arylated pyridazinones using aryldiazonium salts and furan derivatives in mild reaction conditions with water as the solvent. Diazonium salts are highly reactive compounds and so their use results in an important gain in terms of the efficiency of the process. The reaction mechanism is elucidated by DFT calculations and confirmed by empirical tests.Keywords: N-arylated pyridazinones, aryldiazonium salts, DFT calculations.

Les piridazinones són compostos orgànics que es troben en molts fàrmacs, en pesticides i en productes naturals amb activitat biològica. Fins al moment, s’ha publicat un nombre considerable de rutes sintètiques sobre l’obtenció de piridazinones, tot i que sols unes poques descriuen formes eficients de preparar piridazinones N-arilades. A diferència dels mètodes publicats a la bibliografia, en què se solen utilitzar condicions de reacció dràstiques o catalitzadors metàl·lics, el present treball proposa una nova ruta per a l’obtenció de piridazinones N-arilades mitjançant l’ús de sals d’arildiazoni i derivats de furan sota condicions de reacció suaus, incloent-hi l’aigua com a dissolvent. Les sals de diazoni són compostos de gran reactivitat, la qual cosa representa un avantatge important pel que fa a l’eficiència del procés. L’elucidació del mecanisme de la reacció s’ha dut a terme emprant càlculs DFT i s’ha confirmat amb la realització de proves empíriques.Paraules clau: Piridazinones N-arilades, sals d’arildiazoni, càlculs DFT., Pyridazinones are organic compounds that are commonly found in drugs, pesticides, and natural products with biological activity. To date, a considerable number of synthetic routes to obtain pyridazinones have been published although only a few have described efficient pathways to prepare N-arylated pyridazinones. In contrast to methods found in literature in which strong reaction conditions or metallic catalysts are employed, this study proposes a new route to obtain N-arylated pyridazinones using aryldiazonium salts and furan derivatives in mild reaction conditions with water as the solvent. Diazonium salts are highly reactive compounds and so their use results in an important gain in terms of the efficiency of the process. The reaction mechanism is elucidated by DFT calculations and confirmed by empirical tests.Keywords: N-arylated pyridazinones, aryldiazonium salts, DFT calculations.

Depuis quelques années déjà, la technologie s’enracine véritablement dans les enseignements de nos voisins d’outre-Atlantique. Les cours en lignes (Massive Online Open Courses), les Tableaux Interactifs (TIC) n’en sont que quelques exemples. Cette vague du digital s’implante désormais sur le vieux continent. De plus, le monde de l’éducation est sujet à de nombreuses modifications comme en témoigne la « refondation de L’école » entamée par l’Education Nationale. Cependant, cette révolution numérique est-elle vraiment un élément incontournable de l’enseignement de demain ? Sommes-nous certains de la contribution des technologies? Ou suivons-nous, plus simplement, une mode lancée par les Etats-Unis ? Le manque de recul quant aux technologies nous incite à la prudence et à la réflexion. Suivre naïvement une mode sans en cerner tous les avantages, toutes les subtilités ne présente que peu d’intérêts. Et c’est pourquoi, nous avons choisi de nous démarquer de nombre de projets travaillant sur la salle de classe du futur. En effet, l’apport d’une nouvelle technologie, aussi grandiose soit elle, est à double tranchant : Si la nouveauté ne répond pas aux besoins des utilisateurs, elle ne sera guère plus qu’un échec, comme en témoigne l’implantation des tableaux interactifs. Massivement mis en place dans de nombreux établissements, ils sont pourtant peu et mal utilisés ! Aussi, nous prônons un usage réfléchi des technologies dans la salle de classe du futur. Cette année notre projet GAIA consiste en la réalisation d’une maquette à l’échelle 1 de la Salle de Classe du futur. Notre groupe projet est composé de trois composantes dont les formations sont différentes. Tout d’abord, la composante Design Global qui comporte deux étudiantes. Disposant de connaissances nombreuses en architecture, dessins mais également en maitrise de logiciel de conception 3D, elles apportent au groupe une réelle valeur ajoutée. De plus, nous avons la chance de pouvoir compter sur une composante expert, Outgoing