Thermodynamic equilibrium between locally excited and charge-transfer states through thermally activated charge transfer in 1-(pyren-2′-yl)-<i>o</i>-carborane

Ji, Lei; Riese, Stefan; Schmiedel, Alexander; Holzapfel, Marco; Fest, Maximillian; Nitsch, Jörn; Curchod, Basile F. E.; Friedrich, Alexandra; Wu, Lin; Mamari, Hamad H. Al; Hammer, Sebastian; Pflaum, Jens; Fox, Mark A.; Tozer, David J.; Finze, Maik; Lambert, Christoph; Marder, Todd B.

doi:10.1039/d1sc06867a

Cited by 32 publications

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“…In addition, in our analysis of the S 1 state, a new conformation corresponding to a pure CT character (the rightmost conformation in Figure 1 ) is revealed (vide infra) for the first time in the literature as a result of further elongation of the C 1 –C 2 bond. We also note that Ji et al 62 have shown the existence of a similar CT state (C 1 –C 2 = 2.62 Å) for a 1-(pyren-2-yl)- o -carborane system in a very recent study. In this work, this state is named as the S 1 -M (mixed) state, while the twisted confirmation for the 1-(pyren-2-yl)- o -carborane system is called S 1 -CT.…”

Section: Methodssupporting

confidence: 69%

“…While this conformation exhibits a highly energetic S 0 point (1.48 eV as shown in Figure ), the calculated energy barriers on the S 1 surfaces are quite reasonable (0.3–0.4 eV), suggesting that the molecule can reach this geometry via electronic-vibronic couplings upon photoexcitation. In a very recent study, the existence of a similar CT state has also been confirmed for the 1-(pyren-2-yl)- o -carborane system, where the C 1 –C 2 bond length becomes 2.62 Å . In both cases, the energy gap between the S 0 and the S 1 surfaces becomes quite small around this point, which can further increase the nonradiative decay rate according to the energy gap law.…”

Section: Resultsmentioning

confidence: 59%

“…In a very recent study, the existence of a similar CT state has also been confirmed for the 1-(pyren-2-yl)- o -carborane system, where the C 1 –C 2 bond length becomes 2.62 Å. 62 In both cases, the energy gap between the S 0 and the S 1 surfaces becomes quite small around this point, which can further increase the nonradiative decay rate according to the energy gap law. These findings along with previous experimental evidence suggest that the CT state resulting from a fully elongated C 1 –C 2 bond could be an important pathway on the fluorescence quenching of o -CB– Ant and its derivatives.…”

Section: Resultsmentioning

confidence: 65%

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Revisiting the Role of Charge Transfer in the Emission Properties of Carborane–Fluorophore Systems: A TDDFT Investigation

2022

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In this study, we performed a detailed investigation of the S 1 potential energy surface (PES) of o -carborane–anthracene ( o -CB– Ant ) with respect to the C–C bond length on o -CB and the dihedral angle between o -CB and Ant moieties. The effects of different substituents (F, Cl, CN, and OH) on carbon- or boron-substituted o -CB, along with a π-extended acene-based fluorophore, pentacene, on the nature and energetics of S 1 → S 0 transitions are evaluated. Our results show the presence of a non-emissive S 1 state with an almost pure charge transfer (CT) character for all systems as a result of significant C–C bond elongation (C–C = 2.50–2.56 Å) on o -CB. In the case of unsubstituted o -CB– Ant , the adiabatic energy of this CT state corresponds to the global minimum on the S 1 PES, which suggests that the CT state could be involved in emission quenching. Despite large deformations on the o -CB geometry, predicted energy barriers are quite reasonable (0.3–0.4 eV), and the C–C bond elongation can even occur without a noticeable energy penalty for certain conformations. With substitution, it is shown that the dark CT state becomes even more energetically favorable when the substituent shows −M effects (e.g., −CN), whereas substituents showing +M effects (e.g., −OH) can result in an energy increase for the CT state, especially for partially stretched C–C bond lengths. It is also shown that the relative energy of the CT state on the PES depends strongly on the LUMO level of the fluorophore as this state is found to be energetically less favorable compared to other conformations when anthracene is replaced with π-extended pentacene. To our knowledge, this study shows a unique example of a detailed theoretical analysis on the PES of the S 1 state in o -CB– fluorophore systems with respect to substituents or fluorophore energy levels. Our findings could guide future experimental work in emissive o -CB– fluorophore systems and their sensing/optoelectronic applications.

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Section: Methodssupporting

confidence: 69%

Section: Resultsmentioning

confidence: 59%

Section: Resultsmentioning

confidence: 65%

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Revisiting the Role of Charge Transfer in the Emission Properties of Carborane–Fluorophore Systems: A TDDFT Investigation

2022

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“…As such, carboranes have been utilized as important building blocks to construct functional molecules − and tunable pharmacophores (especially for Boron Neutron Capture Therapy (BNCT) drugs). − Among these studies, carboranes are generally treated as an “appended” structural unit. However, it would be more interesting and distinct if carborane-embedded polycyclic systems would be developed with carborane playing a central role. − In such a way, the carborane together with the extended part can serve as a new and united structural skeleton. So far, such a “cage extension strategy” to construct boron cluster-cored polycyclics is much less established in contrast to the classical extension of 2D aromatic rings.…”

Section: Introductionmentioning

confidence: 99%

Facile Construction of New Hybrid Conjugation via Boron Cage Extension

et al. 2023

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Aromatic polycyclic systems have been extensively utilized as structural subunits for the preparation of various functional molecules. Currently, aromatics-based polycyclic systems are predominantly generated from the extension of two-dimensional (2D) aromatic rings. In contrast, polycyclic compounds based on the extension of three-dimensional (3D) aromatics such as boron clusters are less studied. Here, we report three types of boron cluster-cored tricyclic molecular systems, which are constructed from a 2D aromatic ring, a 3D aromatic nido-carborane, and an alkyne. These new tricyclic compounds can be facilely accessed by Pd-catalyzed B–H activation and the subsequent cascade heteroannulation of carborane and pyridine with an alkyne in an isolated yield of up to 85% under mild conditions without any additives. Computational results indicate that the newly generated ring from the fusion of the 3D carborane, the 2D pyridyl ring, and an alkyne is non-aromatic. However, such fusion not only leads to a 1H chemical shift considerably downfield shifted owing to the strong diatropic ring current of the embedded carborane but also devotes to new/improved physicochemical properties including increased thermal stability, the emergence of a new absorption band, and a largely red-shifted emission band and enhanced emission efficiency. Besides, a number of bright, color-tunable solid emitters spanning over all visible light are obtained with absolute luminescence efficiency of up to 61%, in contrast to aggregation-caused emission quenching of, e.g., Rhodamine B containing a 2D-aromatics-fused structure. This work demonstrates that the new hybrid conjugated tricyclic systems might be promising structural scaffolds for the construction of functional molecules.

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“…Ortho -carborane can act as a multifunctional acceptor in charge transfer (CT) processes when connected to π-systems. 62–65 Additionally, carborane itself has been shown to lower the LUMO energy of boranes, especially when the p z orbital on boron aligns with the C1–C2 σ*-anti-bonding orbital. 48,66–68 A similar effect can be observed when the carborane is attached to boron via a conjugated π-system.…”

Section: Introductionmentioning

confidence: 99%

Backbone-controlled LUMO energy induces intramolecular C–H activation inortho-bis-9-borafluorene-substituted phenyl ando-carboranyl compounds leading to novel 9,10-diboraanthracene derivatives

et al. 2022

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Thermodynamic equilibrium between locally excited and charge-transfer states through thermally activated charge transfer in 1-(pyren-2′-yl)-o-carborane

Abstract: Reversible conversion between excited-states is key to many photophysical phenomena. We studied the equilibrium between LE and CT states by time-resolved and temperature-dependent fluorescence, fs- and ns-transient absorption, and LR-TDDFT calculations.

Cited by 32 publications

References 97 publications

Revisiting the Role of Charge Transfer in the Emission Properties of Carborane–Fluorophore Systems: A TDDFT Investigation

Revisiting the Role of Charge Transfer in the Emission Properties of Carborane–Fluorophore Systems: A TDDFT Investigation

Facile Construction of New Hybrid Conjugation via Boron Cage Extension

Backbone-controlled LUMO energy induces intramolecular C–H activation inortho-bis-9-borafluorene-substituted phenyl ando-carboranyl compounds leading to novel 9,10-diboraanthracene derivatives

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