Excited-state Decay Pathways Research Articles

Achieving Ultrafast Charge Transfer by Engineering Multiple Pn Junctions in 3D Hierarchical Cathodes Toward Photo-Chargeable Zinc-Organic Batteries.

Photo-charging zinc ion batteries (PCZIBs) emerge as an innovative approach for the effective utilization and storage of solar energy. However, challenges originating from the suboptimal accessibility of photoexcited charges to electroactive sites severely restrict their practical applications. Herein, a facile methodology to balance light utilization and electrochemical performance by constructing multiple pn junctions in a 3D hierarchical PTCDA-SP/CuZnS photoelectrochemical cathode is reported. DFT calculations reveal that p-type CuZnS can adjust the local electronic environment of n-type PTCDA-SP, facilitating the formation of multiple pn junctions among the interface of this cathode. This unique nanostructure significantly promotes ultrafast charge transfer within 3ps and prevents other undesirable excited state decay pathways, as well as boosts ultrashort photo-response relaxation time less than 20s, resulting in high values of both photo current and voltage of 72.1µA cm-2 and 813mV cm-2 respectively. Additionally, all these carbonyls are responsible for photoelectrochemical Zn2+ storage cascade, ensuring significant improvements in reversible capacities (ca. 32%). This study describes a paradigm of building pn junction on 3D hierarchical cathodes to construct high-performance PCZIBs.

Distinct vibrational motions promote disparate excited-state decay pathways in cofacial perylenediimide dimers.

A complex interplay of structural, electronic, and vibrational degrees of freedom underpins the fate of molecular excited states. Organic assemblies exhibit a myriad of excited-state decay processes, such as symmetry-breaking charge separation (SB-CS), excimer (EX) formation, singlet fission, and energy transfer. Recent studies of cofacial and slip-stacked perylene-3,4:9,10-bis(dicarboximide) (PDI) multimers demonstrate that slight variations in core substituents and H- or J-type aggregation can determine whether the system follows an SB-CS pathway or an EX one. However, questions regarding the relative importance of structural properties and molecular vibrations in driving the excited-state dynamics remain. Here, we use a combination of two-dimensional electronic spectroscopy, femtosecond stimulated Raman spectroscopy, and quantum chemistry computations to compare the photophysics of two PDI dimers. The dimer with 1,7-bis(pyrrolidin-1'-yl) substituents (5PDI2) undergoes ultrafast SB-CS from a photoexcited mixed state, while the dimer with bis-1,7-(3',5'-di-t-butylphenoxy) substituents (PPDI2) rapidly forms an EX state. Examination of their quantum beating features reveals that SB-CS in 5PDI2 is driven by the collective vibronic coupling of two or more excited-state vibrations. In contrast, we observe signatures of low-frequency vibrational coherence transfer during EX formation by PPDI2, which aligns with several previous studies. We conclude that key electronic and structural differences between 5PDI2 and PPDI2 determine their markedly different photophysics.

Fused Azulenyl Squaraine Derivatives Improve Phototheranostics in the Second Near-Infrared Window by Concentrating Excited State Energy on Non-Radiative Decay Pathways.

The second near-infrared (NIR-II) theranostics offer new opportunities for precise disease phototheranostic due to the enhanced tissue penetration and higher maximum permissible exposure of NIR-II light. However, traditional regimens lacking effective NIR-II absorption and uncontrollable excited-state energy decay pathways often result in insufficient theranostic outcomes. Herein a phototheranostic nano-agent (PS-1 NPs) based on azulenyl squaraine derivatives with a strong NIR-II absorption band centered at 1092 nm is reported, allowing almost all absorbed excitation energy to dissipate through non-radiative decay pathways, leading to high photothermal conversion efficiency (90.98 %) and strong photoacoustic response. Both in vitro and in vivo photoacoustic/photothermal therapy results demonstrate enhanced deep tissue cancer theranostic performance of PS-1 NPs. Even in the 5 mm deep-seated tumor model, PS-1 NPs demonstrated a satisfactory anti-tumor effect in photoacoustic imaging-guided photothermal therapy. Moreover, for the human extracted tooth root canal infection model, the synergistic outcomes of the photothermal effect of PS-1 NPs and 0.5 % NaClO solution resulted in therapeutic efficacy comparable to the clinical gold standard irrigation agent 5.25 % NaClO, opening up possibilities for the expansion of NIR-II theranostic agents in oral medicine.

Shortwave infrared polymethine dyes for bioimaging: ultrafast relaxation dynamics and excited-state decay pathways.

Excited-state relaxation in two prototypical shortwave infrared (SWIR) polymethine dyes developed for bioimaging, heptamethine chromenylium Chrom7 and flavylium Flav7, is studied by means of femtosecond transient absorption with broadband ultraviolet-to-SWIR probing complemented by steady-state and time-resolved fluorescence and phosphorescence measurements. The relaxation processes of the dyes in dichloromethane are resolved with sub-100 fs temporal resolution using SWIR, near-IR, and visible photoexcitation. Different population members of the ground-state inhomogeneous ensemble are found to equilibrate via skeletal deformation changes with time constants of 90 fs and either 230 fs (Chrom7) and 350 fs (Flav7) followed by slower evolution matching the 1-ps timescale of diffusive solvation dynamics. Molecules excited into high-lying singlet electronic states (Sn) by visible excitation repopulate with time constants of 400 fs (Chrom7) and 450 fs (Flav7) the corresponding first excited singlet S1 states, which decay within several hundreds of picoseconds in dichloromethane and chloroform solvents. Vibrational relaxation in S1 for both Chrom7 and Flav7 in dichloromethane occurs with time constants of 350 and 800 fs for excess of vibrational energy of ∼1000 and 10 000 cm-1 deposited by near-IR and visible excitation, respectively. Two competing non-radiative processes are present in S1: temperature-independent internal conversion, and thermally-activated twisting about a carbon-carbon bond of the conjugated chain, which is substantial at room temperature but essentially nonreactive, producing traces of isomer product. Intersystem crossing in S1, and thus the triplet quantum yield, is minor. The importance of absorption bands from the excited S1 state in applications requiring high-intensity excitation conditions is discussed.

Laser Interfaced Mass Spectrometry of the Sunscreen Molecule Octocrylene Demonstrates that Protonation Does Not Impact Photostability

AbstractOctocrylene (OCR) is a widely used organic sunscreen molecules, and is a dominant component of many sunscreen formulations. Here, we perform the first measurements on the protonated form of OCR, i. e. [OCR+H]+, to probe whether protonation affects the molecule's photostability. The novel photochemical technique of UV laser‐interfaced mass spectrometry is employed from 400–216 nm, revealing that the electronic absorption spectrum of OCR across the S1 and S2 states red shift by 40 nm upon protonation. Our measurements reveal that [OCR+H]+ predominantly undergoes photofragmentation into the m/z 250 and 232 ionic products, associated with loss of its bulky alkyl side chain, and subsequent loss of water, respectively. We compare the photochemical fragmentation results with higher‐energy collisional dissociation results to investigate the nature of the photodynamics that occur following UV absorption. The excited state decay pathways over the S1 and S2 excited states of [OCR+H]+ are associated with statistical fragmentation in line with dominant ultrafast decay. This behaviour mirrors that of neutral OCR, demonstrating that protonation does not affect the ultrafast decay pathways of this sunscreen molecule. We discuss our results in the context of the known breakdown of OCR into benzophenone, identifying a potential photoactivated pathway to benzophenone formation in solution.

CASPT2//CASSCF studies on mechanistic photophysics of 3-hydroxyflavone

3-Hydroxyflavone (3-HF) as the backbone of flavonols has been extensively studied on the dual fluorescence and excited-state intramolecular proton transfer (ESIPT) after photoexcitation. However, its detailed excited-state relaxation mechanism is still unclear. Herein, the minimum-energy structures, conical intersections and singlet–triplet crossing points of 3-HF in the 1ππ∗, 1nπ∗, 3ππ∗, 3nπ∗, and S0 states in the gas phase were first optimized by the CASPT2//CASSCF method. Then, the minimum-energy proton transfer (MEPT) and excited-state decay (ESD) pathways were calculated as well. Based on the calculation results, we proposed several possible ESD pathways from the initially populated bright S2(ππ*) state. The major channel is singlet-involved and stretch-torsion coupled ESIPT pathway. 3-HF in normal (N) form first undergoes efficient 1ππ* ESIPT with a small barrier of 2.2 kcal/mol to yield the 1ππ* proton-transferred tautomer (T). Subsequently, the T tautomer approaches the nearby accessible S1/S0 conical intersection and then occurs internal conversion (IC) to fall back to the S0 state. Finally, the S0 species quickly transfers into the N conformer via the reverse ground state intramolecular proton transfer (GSIPT) to realize the ground-state recovery. In addition, the minor ESD pathways are involved less efficient intersystem crossing (ISC) processes. The present work could provide insights into understanding the photophysics of flavonols and their derivatives.

Fluorescence Modulation by Amines: Mechanistic Insights into Twisted Intramolecular Charge Transfer (TICT) and Beyond

Amine groups are common constituents of organic dyes and play important roles in tuning fluorescence properties. In particular, intensive research works have demonstrated the tendency and capabilities of amines in influencing chromophore brightness. Such properties have been explained by multiple mechanisms spanning from twisted intramolecular charge transfer (TICT) to the energy gap law and beyond, which introduce additional nonradiative energy dissipation pathways. In this review, we aim to provide a focused overview of the mechanistic insights mainly for the TICT mechanism, accompanied by a few other less common or influential fluorescence quenching mechanisms in the amine-containing fluorescent molecules. Various aspects of current scientific findings including the rational design and synthesis of organic chromophores, theoretical calculations, steady-state and time-resolved electronic and vibrational spectroscopies are reviewed. These in-depth understandings of how the amine groups with diverse chemical structures at various atomic sites affect excited-state nonradiative decay pathways will facilitate the strategic and targeted development of fluorophores with desired emission properties as versatile chemosensors for broad applications.

Excited-State Deactivation Mechanism of 3,5-bis(2-hydroxyphenyl)-1H-1,2,4-triazole: Electronic Structure Calculations and Nonadiabatic Dynamics Simulations.

3,5-bis(2-Hydroxyphenyl)-1H-1,2,4-triazole (bis-HPTA) has attracted wide attention due to the important application in the detection of microorganisms and insecticidal activity. However, the mechanisms of excited-state intramolecular proton transfer (ESIPT) process and decay pathways are still a matter of debate. In this work, we have comprehensively investigated the photodynamics of bis-HPTA by executing combined electronic structure calculations and nonadiabatic surface-hopping dynamics simulations. Based on the computed electronic structure and dynamics information, we propose two nonadiabatic deactivation channels that efficiently populate the ground state from the Franck-Condon region. In the first one, after being excited to the bright S1 state, bis-HPTA molecule undergoes an ultrafast and barrierless ESIPT-1 process. Then, the system encounters with an energetically accessible S1/S0 conical intersection (CI), which funnels the system to the ground state speedily. Afterward, the keto species either arrives at the keto product or return to its enol species via a ground-state proton transfer in the S0 state. In the other excited-state decay channel, the S1 system hops to the ground state through a different CI, which involves the ESIPT-2 process. In our dynamics simulations, about 79.6% of the trajectories decay to the S0 state via the first CI, while the remaining ones employ the second conical intersection. The results of dynamics simulations also demonstrated that the lifetime of the S1 state is estimated as 315 fs. The present work will give elaborating mechanistic information of similar compounds in various environments.

Nanophotonic Approach to Study Excited-State Dynamics in Semiconductor Nanocrystals.

In semiconductor nanocrystals, excited electrons relax through multiple radiative and nonradiative pathways. This complexity complicates characterization of their decay processes with standard time- and temperature-dependent photoluminescence studies. Here, we exploit a simple nanophotonic approach to augment such measurements and to address open questions related to nanocrystal emission. We place nanocrystals at different distances from a gold reflector to affect radiative rates through variations in the local density of optical states. We apply this approach to spherical CdSe-based nanocrystals to probe the radiative efficiency and polarization properties of the lowest dark and bright excitons by analyzing temperature-dependent emission dynamics. For CdSe-based nanoplatelets, we identify the charge-carrier trapping mechanism responsible for strongly delayed emission. Our method, when combined with careful modeling of the influence of the nanophotonic environment on the relaxation dynamics, offers a versatile strategy to disentangle the complex excited-state decay pathways present in fluorescent nanocrystals as well as other emitters.

Energetic Basis and Design of Enzyme Function Demonstrated Using GFP, an Excited-State Enzyme.

The past decades have witnessed an explosion of de novo protein designs with a remarkable range of scaffolds. It remains challenging, however, to design catalytic functions that are competitive with naturally occurring counterparts as well as biomimetic or nonbiological catalysts. Although directed evolution often offers efficient solutions, the fitness landscape remains opaque. Green fluorescent protein (GFP), which has revolutionized biological imaging and assays, is one of the most redesigned proteins. While not an enzyme in the conventional sense, GFPs feature competing excited-state decay pathways with the same steric and electrostatic origins as conventional ground-state catalysts, and they exert exquisite control over multiple reaction outcomes through the same principles. Thus, GFP is an "excited-state enzyme". Herein we show that rationally designed mutants and hybrids that contain environmental mutations and substituted chromophores provide the basis for a quantitative model and prediction that describes the influence of sterics and electrostatics on excited-state catalysis of GFPs. As both perturbations can selectively bias photoisomerization pathways, GFPs with fluorescence quantum yields (FQYs) and photoswitching characteristics tailored for specific applications could be predicted and then demonstrated. The underlying energetic landscape, readily accessible via spectroscopy for GFPs, offers an important missing link in the design of protein function that is generalizable to catalyst design.

Quantum mechanics/molecular mechanics studies on excited state decay pathways of 5-azacytosine in aqueous solution

In this work, we have used the QM(CASPT2//CASSCF)/MM approach to study the photophysical properties and relaxation mechanism of 5-azacytosine (5-AC) in aqueous solution. Based on the relevant minimum-energy structures and intersection structures, and excited-state decay paths in the S1, S2, T1, T2, and S0 states, several feasible excited-state nonradiative decay channels from the initially populated S2(ππ*) state are proposed. Two major channels are singlet-mediated nonradiative pathways, in which the S2 system will internally convert (IC) to the S0 state directly or mediated by the 1nπ* state via a 1ππ*/1nπ* conical intersection. The minor ones are related to intersystem crossing (ISC) processes. The system would populate to the T1 state via the S2 → S1 → T1 or S2 → T2 → T1 ISC process, followed by further decay to the S0 state via the transition from T1 to S0. However, due to small spin-orbit couplings (SOCs) at the singlet-triplet crossing points, the related ISC would be less efficient and probably take longer. The present work rationalizes the ultrafast excited-state decay dynamics of 5-AC in aqueous solution and its low quantum yields of triplets and fluorescence. It provides important mechanistic insights into understanding 5-AC's derivatives and analogues.

Mechanistic Investigation of Molybdenum Disulfide Defect Photoluminescence Quenching by Adsorbed Metallophthalocyanines.

Lattice defects play an important role in determining the optical and electrical properties of monolayer semiconductors such as MoS2. Although the structures of various defects in monolayer MoS2 are well studied, little is known about the nature of the fluorescent defect species and their interaction with molecular adsorbates. In this study, the quenching of the low-temperature defect photoluminescence (PL) in MoS2 is investigated following the deposition of metallophthalocyanines (MPcs). The quenching is found to significantly depend on the identity of the phthalocyanine metal, with the quenching efficiency decreasing in the order CoPc > CuPc > ZnPc, and almost no quenching by metal-free H2Pc is observed. Time-correlated single photon counting (TCSPC) measurements corroborate the observed trend, indicating a decrease in the defect PL lifetime upon MPc adsorption, and the gate voltage-dependent PL reveals the suppression of the defect emission even at large Fermi level shifts. Density functional theory modeling argues that the MPc complexes stabilize dark negatively charged defects over luminescent neutral defects through an electrostatic local gating effect. These results demonstrate the control of defect-based excited-state decay pathways via molecular electronic structure tuning, which has broad implications for the design of mixed-dimensional optoelectronic devices.

Impact of Ring-Fusion on the Excited State Decay Pathways of N-Annulated Perylene Diimides

N-Annulated perylene diimide (PDI) dimers offer added advantages over conventional (non-annulated) dimers or S/Se-annulated dimers due to the two extra positions of functionalization that they prov...

Photophysics of First-Generation Photomolecular Motors: Resolving Roles of Temperature, Friction, and Medium Polarity.

Light-driven unidirectional molecular rotary motors have the potential to power molecular machines. Consequently, optimizing their speed and efficiency is an important objective. Here, we investigate factors controlling the photochemical yield of the prototypical unidirectional rotary motor, a sterically overcrowded alkene, through detailed investigation of its excited-state dynamics. An isoviscosity analysis of the ultrafast fluorescence decay data resolves friction from barrier effects and reveals a 3.4 ± 0.5 kJ mol-1 barrier to excited-state decay in nonpolar media. Extension of this analysis to polar solvents shows that this barrier height is a strong function of medium polarity and that the decay pathway becomes near barrierless in more polar media. Thus, the properties of the medium can be used as a route for controlling the motor's excited-state dynamics. The connection between these dynamics and the quantum yield of photochemical isomerization is probed. The photochemical quantum yield is shown to be a much weaker function of solvent polarity, and the most efficient excited-state decay pathway does not lead to a strongly enhanced quantum yield for isomerization. These results are discussed in terms of the solvent dependence of the complex multidimensional excited-state reaction coordinate.

Solvatochromism and excited-state characteristics of fluorenone-1-carboxylic acid

The solvatochromism of the fluorenone derivative 9-fluorenone-1-carboxylic acid (9F1C) was examined in binary cyclohexane-tetrahydrofuran mixtures, along with a theoretical investigation of possible excited state decay pathways. This fluorenone derivative differs from many previously investigated derivatives in that it possesses an electron withdrawing substituent and possibly undergoes intramolecular hydrogen bonding and proton transfer. A conventional Lippert-Mataga analysis was applied to the measured steady-state absorption and emission spectra to estimate the dipole moment difference between ground and emitting excited states. The estimated difference of ~2.8 D was found to be slightly larger than the average value of previously estimated differences for unsubstituted fluorenone (~2.4 D). The 9F1C derivative also differed from unsubstituted fluorenone in that fluorescence emission decreased, rather than increased, with increasing solvent polarity. Interpreting the possible cause of this difference prompted time-dependent density functional theory (TD-DFT) calculations of the relative energies of non-hydrogen bonded and intra-molecular hydrogen bonded excited states. These calculations suggested that an explanation for the decrease in emission for non-hydrogen bonded species could be enhancement of an intersystem-crossing (ISC) pathway. However, these same calculations suggested this explanation could not account for possible decreased emission from intra-molecular hydrogen-bonded species.

Ab Initio Nonadiabatic Molecular Dynamics with Hole-Hole Tamm-Dancoff Approximated Density Functional Theory.

The study of photoinduced dynamics in chemical systems necessitates accurate and computationally efficient electronic structure methods, especially as the systems of interest grow larger. The linear response hole-hole Tamm-Dancoff approximated (hh-TDA) density functional theory method was recently proposed to satisfy such demands. The N-electron electronic states are obtained by means of double annihilations on a doubly anionic (N + 2)-electron reference state, allowing for the ground and excited states to be formed on the same footing and thus enabling the correct description of conical intersections. Dynamic electron correlation effects are incorporated by means of the exchange-correlation functional. The accuracy afforded by the simultaneous treatment of static and dynamic correlation in addition to the relatively low computational cost, comparable to that of time-dependent density functional theory (TDDFT), makes it a promising ab initio electronic structure method for on-the-fly generation of potential energy surfaces in nonadiabatic dynamics simulations of photochemical systems, particularly those for which the nπ* and ππ* electronic excitations are most relevant. Here, we apply the hh-TDA method to nonadiabatic dynamics simulations of prototypical photochemical processes. First, we demonstrate the ability of hh-TDA to adequately describe conical intersection geometries. We next examine its ability to describe the ultrafast excited state dynamics of photoexcited ethylene through an ab initio multiple spawning (AIMS) dynamics simulation. Finally, we present an alternative variant of the hh-TDA method, which uses orbitals from a fractional occupation number Kohn-Sham (FON-KS) calculation applied to an ensemble with N-electrons. The resulting method is termed floating occupation molecular orbital hh-TDA (FOMO-hh-TDA). This scheme allows us to combine hh-TDA with global hybrid functionals and allows us to avoid unbound valence orbitals that may result from an (N + 2)-electron self-consistent field (SCF) procedure. FOMO-hh-TDA-BHLYP faithfully reproduces the nonadiabatic dynamics of trans-azobenzene (TAB) and is used to characterize the excited state decay pathways from the first (nπ*) excited state.

Theoretical Insights into the Excited State Decays of a Donor-Acceptor Dyad: Is the Twisted and Rehybridized Intramolecular Charge-Transfer State Involved?

The twisted intramolecular charge transfer has been proposed for a number of years and widely accepted to explain the excited-state dynamics of organic molecules. Recently, a new state termed as "twisted and rehybridized intramolecular charge transfer" has been proposed to explain the excited-state dynamics of an aniline-triazine electron donor-acceptor dyad with an alkyne spacer based on ultrafast time-resolved spectroscopy. However, the change of the geometries along the excited-state decay pathway remains unknown. In this study, by optimization of the excited-state geometry of the donor-acceptor dyad and potential energy surface scan along the twisting angle, we successfully reproduce the experimentally observed band in time-resolved infrared absorption spectroscopy. Our calculation results demonstrated that the rehybridization process is not involved and only the twisted intramolecular charge transfer state is formed. Moreover, we located a minimum energy conical intersection between the ground and first excited-state of the donor-acceptor dyad, which is easily reached and corresponding to the primary nonradiative decay pathway of the donor-acceptor dyad. The energy of minimum energy conical intersection is solvent-dependent and consistent with the experimentally observed solvent-dependent lifetime of excited state.

Nonadiabatic Dynamics Simulations on Early-Time Photochemistry of Spirobenzopyran.

Photoinduced ring-opening, decay, and isomerization of spirobenzopyran have been explored by the OM2/MRCI nonadiabatic dynamics simulations based on Tully's fewest-switches surface hopping scheme. The efficient S1 to S0 internal conversion as observed in experiments is attributed to the existence of two efficient excited-state decay pathways. The first one is related to the C-N dissociation, and the second one is done to the C-O dissociation. The C-O dissociation pathway is dominant, and more than 90% trajectories decay to the S0 state via the C-O bond-fission related S1/S0 conical intersections. Near these regions in the S0 state, trajectories can either return to spirobenzopyran or proceed to various intermediates including merocyanine via a series of bond rotations. Our nonadiabatic dynamics simulations also demonstrate that the hydrogen-out-of-plane (HOOP) motion is important for efficient and ultrafast excited-state deactivation. On the other hand, we have also found that the replacement of methyl groups by hydrogen atoms in spirobenzopyran can artificially introduce different intramolecular hydrogen transfers leading to hydrogen-transferred intermediates. This finding is important for the community and demonstrates that such a kind of structural truncation, sometimes, could be problematic, leading to incorrect photodynamics. Our present work provides valuable insights into the photodynamics of spirobenzopyran, which could be helpful for the design of spiropyran-based photochromic materials.

Computing the Ultrafast and Radiationless Electronic Excited State Decay of Cytosine and 5‐methyl‐cytosine Cations: Uncovering the Role of Dynamic Electron Correlation

AbstractPhotoionisation in DNA, i. e. the process of photoinduced electron removal from the chromophoric species – the nucleobases – leading to their cationic form, has been scarcely studied despite being considered to be responsible for significant damaging instances in our genetic material. In this contribution we theoretically characterise the electronic ground and excited state decay pathways of cationic DNA nucleobase cytosine+ and its epigenetic derivative 5‐methyl‐cytosine+, including the effects of dynamic electron correlation on energies and geometries of minima and conical intersections. We do this by comparing the results of XMS‐CASPT2 calculations with CASSCF estimates and we find some significant differences between the results of these two methods. In particular, including dynamic electron correlation is found to significantly reduce the barrier to access the conical intersection. We find notable similarities in both cytosine and 5‐methyl‐cytosine cations, and accessible conical intersections in the vicinity of the Franck‐Condon region are found. This points towards an ultrafast depopulation of their electronic excited states. Moreover, the shape of the ground state potential energy surface strongly directs the decaying excited state population towards the cationic ground state minimum on ultrafast timescales, preventing photo‐fragmentation and thus explaining their photostability. To better compare our calculations with the available experimental data we compute the UV (ground and excited state) and IR absorptions.

Stereoselective Excited-State Isomerization and Decay Paths in cis-Cyclobiazobenzene.

Herein, we have employed OM2/MRCI-based full-dimensional nonadiabatic dynamics simulations to explore the photoisomerization and subsequent excited-state decay of a macrocyclic cyclobiazobenzene molecule. Two S1/S0 conical intersection structures are found to be responsible for the excited-state decay. Related to these two conical intersections, we found two stereoselective photoisomerization and excited-state decay pathways, which correspond to the clockwise and counterclockwise rotation motions with respect to the N═N bond of the azo group. In both pathways, the excited-state isomerization is ultrafast and finishes within ca. 69 fs, but the clockwise isomerization channel is much more favorable than the counterclockwise one with a ratio of 74% versus 26%. Importantly, the present work demonstrates that stereoselective pathways exist not only in the photoisomerization of isolated azobenzene (AB)-like systems but also in macrocyclic systems with multiple ABs. This finding could provide useful insights for understanding and controlling the photodynamics of macrocyclic nanostructures with AB units as the main building units.