Synthesis of π-Conjugated Chiral Aza/Boracyclophanes with a meta and para Substitution.

We herein describe the synthesis of a new class of axially chiral aza/boracyclophanes (BDN1, BXN1, BDB1 and BXB1) using binaphthyls as chiral building blocks and the main-group (B/N) chemistry with tunable electronic effects. All macrocycles substituted with triarylamine donors or triarylborane acceptors are strongly luminescent. These macrocycles showed two distinct meta and para π-conjugation pathways, leading to the formation of quasi figure-of-eight and square-shaped conformations. Interestingly, comparison of such structural models revealed that the former type of macrocycles BXN1 and BXB1 gave higher racemization barriers relative to the other ones. The results reported here may provide a new approach to engineer the optical stability of π-conjugated chiral macrocycles by controlling π-substitution patterns. The ring constraints induced by macrocyclization were also demonstrated to contribute to the configurational persistence as compared with the open-chain analogues p-BTT and m-BTT.

Theoretical Study of the Photocyclization Reaction-Induced Dual Aggregation-Induced Emission Phenomenon.

Photochromic molecules with aggregation-induced emission (AIE) effects are of great value and prospective in various practical applications. To explore its inherent mechanism, the open isomer ap-BBTE and the closed isomer c-BBTE were chosen to perform the theoretical calculation using the quantum mechanics/molecular mechanics model combined with thermal vibration correlation function formalism. The calculations show that the photocyclization (PC) reaction from ap-BBTE to c-BBTE facilitates an improvement in the AIE effect. It is found that the fluorescence quantum yield (ΦF) enhancement of ap-BBTE is attributed to the restriction of the low-frequency rotational motion of the benzothiophene moiety and the high-frequency stretching vibrations of the C-C bond between the benzothiophene and benzylbis(thiadiazole) vinyl groups after aggregation. For c-BBTE, the increase in ΦF upon aggregation is mainly due to the suppression of the high-frequency stretching vibration of the C-C bond between the benzothiophene and the benzobis(thiadiazole) vinyl groups. In addition, the AIE effect was also enhanced from ap-BBTE to c-BBTE, which is consistent with the experimental phenomenon. The corresponding emission spectrum red-shifted from ap-BBTE to c-BBTE in both dilute solution and the crystalline state due to the improved intramolecular conjugation of c-BBTE. Moreover, the PC reaction from ap-BBTE to c-BBTE easily occurs in an excited state with a low energy barrier transition state by forming a C-C bond between benzothiophene groups effectively in dilute solution. Our calculations provide theoretical guidance for the further rational design of efficient AIE luminogens.

Theoretical Understanding on the Facilitated Photoisomerization of a Carbonyl Supported Borane System.

Boron compound BOMes2 containing an internal B-O bond undergoes highly efficient photoisomerization, followed by sequential structural transformations, resulting in a rare eight-membered B, O-heterocycle (S. Wang, et al. Org. Lett. 2019, 21, 5285-5289). In this work, the detailed reaction mechanisms of such a unique carbonyl-supported tetracoordinate boron system in the first excited singlet (S1 ) state and the ground (S0 ) state were investigated by using the complete active space self-consistent field and its second-order perturbation (MS-CASPT2//CASSCF) method combined with time-dependent density functional theory (TD-DFT). Moreover, an imine-substituted tetracoordinated organic boron system (BNMes2 ) was selected for comparative study to explore the intrinsic reasons for the difference in reactivity between the two types of compounds. Steric factor was found to influence the photoisomerization activity of BNMes2 and BOMes2 . These results rationalize the experimental observations and can provide helpful insights into understanding the excited-state dynamics of heteroatom-doped tetracoordinate organoboron compounds, which facilitates the rational design of boron-based materials with superior photoresponsive performances.

A theoretical study on the photochemical generation of phenylborylene from phenyldiazidoborane.

Organic borylenes are a kind of highly reactive species, which play important roles in a lot of reactions as vigorous intermediates. In this work, we investigated the photochemical generation mechanisms of phenylborylene (PhB) together with the side product N-phenylnitrenoiminoborane (PhNBN) from phenyldiazidoborane (PhBN6) by extrusion of dinitrogen in the two lowest electronic singlet states (S0 and S1) based on the complete active space self-consistent field (CASSCF) and its second-order perturbation (CASPT2) methods combined with time-dependent density functional theory (TD-DFT) calculations. Our results show that the reaction PhBN6 → PhB + 3N2 involves stepwise N2 extrusion three times and the azido region rearrangement. Moreover, we found that the studied photo-induced processes are kinetically feasible because the highest energy barrier is only 0.36 eV and excitation with light of wavelength 254 nm can provide enough excess energy to overcome these energy barriers. Importantly, we revealed that several conical intersections between S1 and S0 states participate and facilitate the studied photochemical processes. Our results not only clarify the experimental observations, (H. F. Bettinger, J. Am. Chem. Soc. 2006, 128, 2534), but also provide valuable insights into borylene chemistry.

Cooperative multiple interactions of donor-π-acceptor dyes enhance the efficiency and stability of perovskite solar cells.

Surface passivation by organic dyes has been an effective strategy for simultaneous enhancement of the efficiency and stability of perovskite solar cells. However, lack of in-depth understanding of how subtle structural changes in dyes leads to distinctly different passivation effects is a challenge for screening effective passivation molecules (PMs). In an experiment done by Han et al. (Adv. Energy Mater., 2019, 9, 1803766), three donor-π-acceptor (D-π-A) dyes (SP1, SP2, and SP3) with distinct electron donors have been applied to passivate the perovskite surface, where the efficiency and stability of PSCs are quite different. Herein, we carried out first-principles calculations and ab initio molecular dynamics (AIMD) simulations on the structures and electronic properties of SP1, SP2, SP3, and their passivated perovskite surfaces. Our results showed that SP3 enhances the carrier transfer rate, electric field, and absorption region compared to SP1 and SP2. Moreover, AIMD simulations reveal that the cooperative multiple interactions of O-Pb, S-Pb, and H-I between SP3 and the perovskite surface result in a stronger passivation effect in a humid environment than that of SP1 and SP2. This work is expected to pave the way for screening dye passivation molecules to endow perovskite solar cells with high efficiency and stability.

Designing Benzodithiophene-Based Small Molecule Donors for Organic Solar Cells by Regulation of Halogenation Effects.

The donors are key components of organic solar cells (OSCs) and play crucial roles in their photovoltaic performance. Herein, we designed two new donors (BTR-γ-Cl and BTR-γ-F) by finely optimizing small molecule donors (BTR-Cl and BTR-F) with a high performance. The optoelectronic properties of the four donors and their interfacial properties with the well-known acceptor Y6 were studied by density functional theory and time-dependent density functional theory. Our calculations show that the studied four donors have large hole mobility and strong interactions with Y6, where the BTR-γ-Cl/Y6 has the largest binding energy. Importantly, the proportion of charge transfer (CT) states increases at the BTR-γ-Cl/Y6 (50%) and BTR-γ-F/Y6 (45%) interfaces. The newly designed donors are more likely to achieve CT states through intermolecular electric field (IEF) and hot exciton mechanisms than the parent molecules; meanwhile, donors containing Cl atoms are more inclined to produce CT states through the direct excitation mechanism than those containing F atoms. Our results not only provided two promising donors but also shed light on the halogenation effects on donors in OSCs, which might be important to design efficient photovoltaic materials.

Incorporation of a Boron-Nitrogen Covalent Bond Improves the Charge-Transport and Charge-Transfer Characteristics of Organoboron Small-Molecule Acceptors for Organic Solar Cells.

An organoboron small-molecular acceptor (OSMA) MB←N containing a boron-nitrogen coordination bond (B←N) exhibits good light absorption in organic solar cells (OSCs). In this work, based on MB←N, OSMA MB-N, with the incorporation of a boron-nitrogen covalent bond (B-N), was designed. We have systematically investigated the charge-transport properties and interfacial charge-transfer characteristics of MB-N, along with MB←N, using the density functional theory (DFT) and the time-dependent density functional theory (TD-DFT). Theoretical calculations show that MB-N can simultaneously boost the open-circuit voltage (from 0.78 V to 0.85 V) and the short-circuit current due to its high-lying lowest unoccupied molecular orbital and the reduced energy gap. Moreover, its large dipole shortens stacking and greatly enhances electron mobility by up to 5.91 × 10-3 cm2·V-1·s-1. Notably, the excellent interfacial properties of PTB7-Th/MB-N, owing to more charge transfer states generated through the direct excitation process and the intermolecular electric field mechanism, are expected to improve OSCs performance. Together with the excellent properties of MB-N, we demonstrate a new OSMA and develop a new organoboron building block with B-N units. The computations also shed light on the structure-property relationships and provide in-depth theoretical guidance for the application of organoboron photovoltaic materials.

Understanding of Photo-Induced Reversible Rearrangement from Borepin to Borirane.

The first reversible photoisomerization between a borepin and a borirane was reported in the photo-induced reactions of B(npy)Ar2 (npy=2-(naphthalen-1-yl) pyridine, Ar=phenyl or electron rich aryl; S. Wang, et al. Angew. Chem. Int. Ed. 2019, 58, 6683-6687). In this work, the detailed mechanisms of the unprecedented reversible photoisomerization between the borepin (compound a) and the borirane (compound b) of B(npy)Ph2 in the first excited singlet (S1 ) state and the ground (S0 ) state were studied by carrying out calculations with the complete active space self-consistent field (CASSCF) and its second-order perturbation (CASPT2) methods combined with time-dependent density functional theory (TD-DFT). The calculation results show that photoexcitation of a-S0 at 365 nm and b-S0 at 450 nm populate their S1 state with evident charge transfer characteristics. The photoisomerization is triggered in the S1 state and ends in the S0 state, at which the intersection points in a (S1 /S0 )x intersection seam participate in and promote phenyl migration and ring-closure processes. Furthermore, we reveal that the not large energy difference (less than 0.6 eV) and similar conjugation properties of π electrons between a-S0 and b-S0 are responsible for their unique photo-reversible reactivity, compared with those of the isomers of the thermally reversible compound B(ppy)Mes2 . Our results contribute to an understanding of the excited-state reactivity of organoboron compounds and will be useful to support the design of new boron-based photo-responsive materials.

Suppression of reversible photocyclization reaction induced fluorescence enhancement: a theoretical study.

Aggregation-induced emission (AIE) materials with photocyclization (PC) reactions exhibit rich photophysical and photochemical activities. Understanding the mechanism behind is essential to the design of effective AIE materials. Herein, we employ a polarizable continuum model (PCM) and the hybrid quantum mechanics and molecular mechanics (QM/MM) approach, to study the luminescent properties of PC-typed AIEgens, SIP-2 and DPI, in both solution and crystalline states. The calculated results indicate that the fluorescence quantum yields (ΦF) of SIP-2 and DPI under different environments are mainly related to the competition between the PC reaction and aggregation induced restriction of phenyl ring rotational motions. In solution, SIP-2 and DPI undergo PC reactions to form a C-C bond between the phenyl rings A and B, which provides an important non-radiative decay channel and dramatically reduces the fluorescence intensity. Upon aggregation, the restricted rotational motion of rings A and B blocks the PC reaction and reduces the reorganization energy, which lowers the non-radiative decay rate constant (kIC) and benefits the ΦF. This is consistent with the experimental phenomenon that both SIP-2 and DPI exhibit the AIE effect. In addition, the introduction of the rigid spiro backbone of SIP-2 increases the steric effect, further limiting the phenyl ring rotation and PC reaction, resulting in an increase in the fluorescence intensity. Our calculations not only show the detailed mechanism of PC-typed AIEgens but also provide theoretical guidance for the further rational design of efficient AIEgens.

Theoretical insights into photo-induced isomerization mechanisms of phenylsulfinyl radical PhSO˙.

Sulfinyl radicals (R-SO˙) play important roles in lots of reactions, while the isomer oxathiyl radicals (R-OS˙) and the isomerization between them are rarely observed due to the poor stability of R-OS˙. In this work, the complete active space self-consistent field (CASSCF) and its multi-state second order perturbation (MS-CASPT2) methods were employed to study the photo-induced reaction mechanisms of phenylsulfinyl radical PhSO˙ 1 and its isomer phenoxathiyl radical PhOS˙ 2. Our results show that 1 and 2 have similar singly occupied molecular orbitals in the ground state but different properties in the excited state, which determine their diverse behaviors after irradiation. Radical 1 can generate 2 by light irradiation, but 2 produces isomerization product 3 (2-hydroxyphenylthiyl radical) and ring-opening product 4 (acyclic thioketoketene radical) in two paths via S atom migration intermediate Int1 (2-carbonylcyclohexadienthiyl radical). The former path involves consequent hydrogen shift reactions with a strongly exothermic process while the latter path involves both ring-expansion and ring-opening processes with a high barrier, resulting in a structural and energetic preference for the former path. Moreover, we revealed several conical intersections that participate in the reactions and facilitate the photochemical processes. Our calculations not only remain consistent with and clarify the experimental observations (X. Zeng, et al., J. Am. Chem. Soc., 2018, 140(31), 9972-9978) but also enrich the knowledge of sulfinyl radicals and isomer oxathiyl radicals.

Mechanistic Investigation on Chemiluminescent Formaldehyde Probes.

A first-generation pair of chemiluminescent formaldehyde (FA) probes (CFAP540 and CFAP700) was reported recently. CFAP540 and CFAP700, with high selectivity and sensitivity to FA, are, respectively, suitable in cell and in vivo. Experimentalists have confirmed that both probes utilize a general 2-aza-Cope FA-reactive trigger and a chemiluminogenic phenoxydioxetane scaffold. The mechanism and detailed process of CFAP chemiluminescence (CL) remain largely unknown. In the present paper, (time-dependent) density functional theory calculations are performed on the entire reaction process of CFAP540 with FA to produce CL. The calculations elucidated the CL-producing process: FA initiates the decomposition of CFAP540 by dehydration condensation, and a phenoxy 1,2-dioxetane is formed through a series of reactions of aza-Cope rearrangement, hydrolysis of imine, and ß-elimination of alkoxyl group. Afterwards, the produced phenoxy 1,2-dioxetane decomposes to produce the m-oxybenzoate derivative in the first singlet state (S1 ) via two crossings between potential energy surfaces of the ground state (S0 ) and S1 state. This m-oxybenzoate derivative was assigned as the light emitter of the CFAP540 CL. The CL-producing process and assignment of the light emitter of CFAP700 CL are similar with the corresponding ones of CFAP540. By analyzing the D-π-A architecture of the light emitters of CFAP540 and CFAP700, a series of CFAPs is theoretically designed and a scheme to modulate their CL from visible to near-infrared region is proposed by adjusting the length and structure of the π-bridge.

Theoretical design of asymmetric A-D1A'D2-A type non-fullerene acceptors for organic solar cells.

The acceptor in organic solar cells (OSCs) is of paramount importance for achieving a high photovoltaic performance. Based on the well-known non-fullerene acceptor Y6, we designed a set of asymmetric A-D1A'D2-A type new acceptors Y6-C, Y6-N, Y6-O, Y6-Se, and Y6-Si by substituting the two S atoms of one thieno[3,2-b]thiophene unit with C, N, O, Se, and Si atoms, respectively. The electronic, optical, and crystal properties of Y6 and the designed acceptors, as well as the interfacial charge-transfer (CT) mechanisms between the donor PM6 and the investigated acceptors have been systematically studied. It is found that the newly designed asymmetric acceptors possess suitable energy levels and strong interactions with the donor PM6. Importantly, the newly designed acceptors exhibit enhanced light harvesting ability and more CT states with larger oscillator strengths in the 40 lowest excited states. Among the multiple CT mechanisms, the direct excitation of CT states is found to be more favored in the case of PM6/newly designed acceptors than that of PM6/Y6. This work not only offers a set of promising acceptors superior to Y6, but also demonstrates that designing acceptors with asymmetric structure could be an effective strategy to improve the performance of OSCs.

Theoretical Study on Photoisomerization Mechanisms of Diphenyl-Substituted N,C-Chelate Organoboron Compounds.

N,C-chelate organoboron compounds are widely employed as photoresponsive and optoelectronic materials due to their efficient photochromic reactivity. It was found in experiments that two diphenyl-substituted organoboron compounds, namely B(ppy)Ph2 (ppy=2-phenylpyridyl) and B(iba)Ph2 (iba=N-isopropylbenzylideneamine), show distinct photochemical reactivity. B(ppy)Ph2 is inert on irradiation, whereas B(iba)Ph2 undergoes photoinduced transformations, yielding BN-cyclohepta-1,3,5-triene via a borirane intermediate. In this work, the complete active space self-consistent field and its second-order perturbation (CASPT2//CASSCF) methods were used to investigate the photoinduced reaction mechanisms of B(ppy)Ph2 and B(iba)Ph2 . The calculations showed that the two compounds isomerize to borirane in the same way by passing a transition state in the S1 state and a conical intersection between the S1 and S0 states. The energy barriers in the S1 state of 0.54 and 0.26 eV for B(ppy)Ph2 and B(iba)Ph2 , respectively, were explained by analyzing the charge distributions of minima in S0 and S1 states. The results provide helpful insights into the excited-state dynamics of organoboron compounds, which could assist in rational design of boron-based photoresponsive materials.

Insights into the Photoinduced Isomerization Mechanisms of a N,C-Chelate Organoboron Compound: A Theoretical Study.

As the first discovered organoboron compound with photochromic property, B(ppy)Mes2 (ppy=2-phenylpyridine, Mes=mesityl) displays rich photochemistry that constitutes a solid foundation for wide applications in optoelectronic fields. In this work, we investigated the B(ppy)Mes2 to borirane isomerization mechanisms in the three lowest electronic states (S0 , S1 , and T1 ) based on the complete active space self-consistent field (CASSCF) and its second-order perturbation (CASPT2) methods combined with time-dependent density functional theory (TD-DFT) calculations. Our results show that the photoisomerization in the S1 state is dominant, which is initiated by the cleavage of the B-Cppy bond. After overcoming a barrier of 0.5 eV, the reaction pathway leads to a conical intersection between the S1 and S0 states (S1 /S0 )x , from which the decay path may go back to the reactant B(ppy)Mes2 via a closed-shell intermediate (Int1-S0 ) or to the product borirane via a biradical intermediate (Int2-S0 ). Although triplet states are probably involved in the photoinduced process, the possibility of the photoisomerization in T1 state is very small owing to the weakly allowed S1 →T1 intersystem crossing and the high energy barrier (0.77 eV). In addition, we found the photoisomerization is thermally reversible, which is consistent with the experimental observations.

Theoretical study on the photochemistry of furoylazides: Curtius rearrangement and subsequent reactions.

Organic azides are an efficient source of nitrenes, which serve as vigorous intermediates in many useful organic reactions. In this work, the complete active space self-consistent field (CASSCF) and its second-order perturbation (CASPT2) methods were employed to study the photochemistry of 2-furoylazide 1 and 3-furoylazide 5, including the Curtius rearrangement to two furylisocyanates (3 and 7) and subsequent reactions to the final product cyanoacrolein 9. Our calculations show that the photoinduced Curtius rearrangement of the two furoylazides takes place through similar stepwise mechanisms via two bistable furoylnitrenes 2 and 6. However, the decarbonylation and ring-opening process of 7 to 9 prefers a stepwise mechanism involving the 3-furoylnitrene intermediate 8, while 3 to 9 goes in a concerted asynchronous way without the corresponding 2-furoylnitrene intermediate 4. Importantly, we revealed that several conical intersections play key roles in the photochemistry of furoylazides. Our results are not only consistent and also make clear the experimental observations (X. Zeng, et al., J. Am. Chem. Soc., 2018, 140, 10-13), but additionally provide important information on the chemistry of furoylazides and nitrenes.

A Two-Dimensional Spin-Crossover Coordination Polymer Exhibiting Interlayer Multiple C-Hδ+···Hδ--B Dihydrogen Bonds.

The reaction of 1,1,2,2-tetrakis(4-(pyridin-4-yl)phenyl)ethene (tppe) with [Fe(NCBH3)2] produced a two-dimensional coordination polymer [Fe(NCBH3)2(tppe)]n (1), which was pillared in an ABAB manner through interlayer multiple [C-Hδ+···Hδ--B] dihydrogen bonds (DHBs) to form a stable porous three-dimensional (3D) supramolecular structure that showed guest-molecule-dependent spin-crossover behaviors.

Theoretical study on the regioselective photoisomerization of asymmetric N,C-chelate organoboron compounds.

Herein, the complete active space self-consistent field (CASSCF) and its second-order perturbation (CASPT2) methods combined with time-dependent density functional theory (TD-DFT) calculations were employed to investigate the isomerization reaction mechanisms of an asymmetric N,C-chelate organoboron compound, B(ppy)MesPh, in the ground (S0) state and the first singlet excited (S1) state. Our calculations show that isomerizations proceed via different pathways in the S0 and S1 states,; however, the energy barriers for mesityl isomerization are higher than those for phenyl isomerization in both states; this is in good agreement with the experimentally observed regioselectivity (S. Wang, et al. Angew. Chem., Int. Ed., 2017, 56, 6093-6097). Photoisomerization is motivated by charge transfer from two phenyl rings to the pyridyl moiety and initiated by the cleavage of the B-Cppy bond, followed by the formation of a boracyclopropane ring via an (S1/S0)X conical intersection and a biradical intermediate. Both steric and electronic features were found to be important for regioselective photoisomerization. Our results not only shed light on the experimental observations, but also provide valuable details on the excited state dynamics of organoboron compounds and can facilitate further syntheses and applications.

Effect of π-bridge units on properties of A-π-D-π-A-type nonfullerene acceptors for organic solar cells.

Acceptor-π-donor-π-acceptor (A-π-D-π-A)-types of small molecules are very promising nonfullerene acceptors to overcome the drawbacks of fullerene derivatives such as the weak absorption ability and electronic adjustability. However, only few attempts have been made to develop π-bridge units to construct highly efficient acceptors in OSCs. Herein, taking the reported acceptor P1 as a reference, five small-structured acceptors (P2, P3, P4, P5, and P6) have been designed via the replacement of the π-bridge unit. A combination of quantum chemistry and Marcus theory approaches is employed to investigate the effect of different π-bridge units on the optical, electronic, and charge transport properties of P1-P6. The calculation results show that the designed molecules P2 and P5 can become potential acceptor replacements of P1 due to their red-shifted absorption bands, appropriate energy levels, low exciton binding energy, and high electron affinity and electron mobility. Additionally, compared with P3HT/P1, P3HT/P2 and P3HT/P5 exhibit stronger and wider absorption peaks, larger electron transfer distances (DCT), greater transferred charge amounts (Δq), and smaller overlaps (Λ), which shows that P2 and P5 have more significant electron transfer characteristics and favorable exciton dissociation capabilities for enhancing the short-circuit current density (JSC) and thus, they are potential acceptors in OSCs.

Theoretical study of non-Hammett vs. Hammett behaviour in the thermolysis and photolysis of arylchlorodiazirines.

Arylchlorodiazirines (ACDA) are thermal and photochemical precursors of carbenes that form these molecules via nitrogen elimination. We have studied this reaction with multireference quantum chemical methods (CASSCF and CASPT2) for a series of ACDA derivatives with different substitution at the aromatic ring. The calculations explain the different reactivity trends found in the ground and excited state, with good correlation between the calculated barriers and the experimental reaction rates. The ground state mechanism can be described as a reverse cycloaddition with small charge transfer from the aromatic ring to the diazirine moiety. This is consistent with the lack of correlation between the Hammett σ descriptors and the experimental rates. In contrast, the excited state reaction is the cleavage of a single C-N bond mediated by small barriers of 4-6 kcal mol-1. The reaction path goes through a conical intersection with the ground state, which facilitates radiationless decay and explains the disappearance of the transient absorption signal measured experimentally. This leads to a diazomethane intermediate that ultimately yields the carbene. Electronically, excitation to S1 is characterized initially by significant charge transfer from the phenyl ring to the diazirine. The charge transfer is reversed during the C-N cleavage reaction, and this explains the preferential stabilization of the excited-state minimum by polar solvents and electron-donating substituents. Therefore, our calculations reproduce and explain the relationship found experimentally between the Hammett σ+ parameters and the life time of S1 (Y. L. Zhang, et al. J. Am. Chem. Soc., 2009, 131, 16652-16653).

Photochemical Generation of Chiral N,B,X-Heterocycles by Heteroaromatic C-X Bond Scission (X=S, O) and Boron Insertion.

Chiral organoboron compounds with a chelate backbone and mesityl/heterocycle substituents (thienyl, furyl, and derivatives thereof) undergo a quantitative phototransformation that yields rare, chiral N,B,X-containing heterocycles, such as base-stabilized 1,2-thiaborinines and 1,2-oxaborinines. Boriranes were observed as intermediates in some of these transformations. The oxaborinines display further reactivity, generating 4a,12b-dihydrobenzo[h][1,2]oxaborinino[4,3-f]quinolines through a sequential conrotatory electrocyclization and a [1,5]-H shift. The N,B,X-containing heterocycles display strong blue-green to orange-red emission in the solid state. Combined DFT//CASP2T calculations suggest that a common biradical intermediate is responsible for the formation of these compounds as well as their interconversion.