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Radionuclide therapy employing alpha emitters holds great potential for personalized cancer treatment. However, certain challenges remain when designing alpha radiopharmaceuticals, including the lack of stability of used radioconjugates due to nuclear decay events. In this work, ultrasmall silver telluride nanoparticles with a core diameter of 2.1 nm were prepared and radiolabeled with lead‐212 using a chelator‐free method with a radiolabeling efficiency of 75%. The results from the in vitro radiochemical stability assay indicated a very high retention of bismuth‐212 despite the internal conversion effects originating from the decay of 212Pb. To further evaluate the potential of the nanoparticles, they were radiolabeled with indium‐111, and their cell uptake and subcellular distribution were determined in 2D U87 cells, showing accumulation in the nucleus. Although not intentional, it was observed that the indium‐111‐radiolabeled nanoparticles induced efficient tumor cell killing, which was attributed to the Auger electrons emitted by indium‐111. Combining the results obtained in this work with other favorable properties such as fast renal clearance and the possibility to attach targeting vectors on the surface of the nanoparticles, all well‐known from the literature, these ultra‐small silver telluride nanoparticles provide exciting opportunities for the design of theragnostic radiopharmaceuticals. [ABSTRACT FROM AUTHOR]

Femtosecond fluorescence upconversion experiments were combined with CASPT2 and time dependent DFT calculations to characterize the excited state dynamics of the mutagenic etheno adduct 1,N2‐etheno‐2'‐deoxyguanosine (ϵdG). This endogenously formed lesion is attracting great interest because of its ubiquity in human tissues and its highly mutagenic properties. The ϵdG fluorescence is strongly modified with respect to that of the canonical nucleoside dG, notably by an about 6‐fold increase in fluorescence lifetime and quantum yield at neutral pH. In addition, femtosecond fluorescence upconversion experiments reveal the presence of two emission bands with maxima at 335 nm for the shorter‐lived and 425 nm for the longer‐lived. Quantum mechanical calculations rationalize these findings and provide absorption and fluorescence spectral shapes similar to the experimental ones. Two different bright minima are located on the potential energy surface of the lowest energy singlet excited state. One planar minimum, slightly more stable, is associated with the emission at 335 nm, whereas the other one, with a bent etheno ring, is associated with the red‐shifted emission. [ABSTRACT FROM AUTHOR]

Context: It has been reported that photoexcitation of azastilbene compounds like E-1,2-bispyrazinyl-ethylene (bpe) can undergo E → Z photoisomerization of its quaternary salts via the excited triplet state. However, experimentally it is possible to get low fluorescence and photoisomerisation quantum yields in a state with higher internal conversion than intersystem crossing. We modelled bpe and its methylated derivative (bpeMe), as well as its quaternary halogen salts (bpeMeX with X = F−, Cl−, Br− and I−) to study levels of fluorescence, phosphorescence and excited state potential energy surfaces (PES). Results support experimental observations of molecules where the anion of a salt is an efficient electron donor, that molecules with weak electron-donating anions like Cl− to give increased fluorescence and photoisomerization, as compared to molecules with stronger electron-donating anions like I−, which are dominated by competing electron transfer. The fluorescence of bpeMeF and bpeMeCl was found to be stronger than bpeMeBr and bpeMeI. A deep well in the triplet excited state of bpeMeI is considered responsible for the decreased photoisomerization, compared to what was experimentally observed for bpeMeCl. Uniquely, the bpeMeI molecule is characterised by near-zero splitting of the s1 and t1 excited states that can enhance charge transfer. The quaternary salt of bpeMe with stronger electron-donating Br− anion was observed to undergo fluorescence and phosphorescence at much lower energy compared to those with weak electron-donating F− and Cl− anions. This research shows how to control the excited state fluorescence, phosphorescence and isomerization of quaternary halogen salts of methyl derivatives of 1,2-bispyrazinyl-ethylene, which aids experimental design where excited state isomerization is considered. Methods: Geometry optimization, molecular electrostatic potential (MESP), and time dependent density functional theory (TDDFT) calculations were conducted utilizing Gaussian 16 with the B3LYP functional and the 6–31 + G(d,p) basis set. The minimum energy path (MEP) for the E to Z isomerization of the molecules was established employing the Nudged-Elastic-Band (NEB) method, implemented in Orca 4.2. Precise energies of the E → Z isomerization reaction path were determined employing CASSCF and a more accurate multireference method, NEVPT2. [ABSTRACT FROM AUTHOR]

Diamondoids, of which adamantane (C 10 H 16 ) is the simplest representative, constitute an intriguing class of carbon based nanomaterials with interesting chemical, mechanical and opto-electronic properties. While neutral diamondoids have been extensively studied for decades, their cationic counterparts were a subject of recent experimental investigations motivated by their potential role in astrochemistry. Here, we perform a computational study of the adamantane cation (C 10 H 16 + ) complementing the recent experimental findings. Specifically, we extend earlier theoretical work on vibrationally resolved electronic spectroscopy by accounting for the higher lying electronically excited states of the cation in the absorption and photoelectron spectra. We also perform adiabatic and nonadiabatic (surface hopping) molecular dynamics simulations to study (fast) fragmentation processes and electronic relaxation of C 10 H 16 + . Our simulations reveal that after excitation with near-infrared–ultraviolet photons, the adamantane cation undergoes an ultrafast internal conversion to the ground (doublet) state (on a time scale of 10–100 fs depending on initial excitation energy) which can be followed by a fast fragmentation, predominantly H loss. The yield of the ultrafast hydrogen dissociation as a function of excitation energy is reported. [ABSTRACT FROM AUTHOR]

The structure of 74Se at low energy was investigated via spectroscopy of internal conversion electrons at the INFN Legnaro National Laboratories (LNL). A set of internal K-conversion coefficients and monopole transition strengths was measured. A large ρ2(E0;22+→21+)⋅103=210(130) value was deduced. This result, in addition to a low upper limit for the 03+→02+ electron transition, casts in doubt a simple interpretation of the 74Se low-lying structure, in particular the recently proposed spherical, vibrational character. New microscopic beyond-mean-field calculations generally agree with the experimental results and are capable of producing a large ρ2(E0;22+→21+) value, even if still a factor ≈7 smaller than the experiment. Triaxiality and a complex shape-coexistence and mixing scenario seem responsible for this unexpected experimental result.

Abstract Background Radionuclide therapy (RNT) has become a very important treatment modality for cancer nowadays. Comparing with other cancer treatment options, sufficient efficacy could be achieved in RNT with lower toxicity. β− emitters are frequently used in RNT due to the long tissue penetration depth of the β− particles. The dysprosium-166/holmium-166 (166Dy/166Ho) in vivo generator shows great potential for treating large malignancies due to the long half-life time of the mother nuclide 166Dy and the emission of high energy β− from the daughter nuclide 166Ho. However, the internal conversion occurring after β− decay from 166Dy to 166Ho could cause the release of about 72% of 166Ho when 166Dy is bound to conventional chelators. The aim of this study is to develop a nanoparticle based carrier for 166Dy/166Ho in vivo generator such that the loss of the daughter nuclide 166Ho induced by internal conversion is prevented. To achieve this goal, we radiolabelled platinum-gold bimetallic nanoparticles (PtAuNPs) and core–shell structured gold nanoparticles (AuNPs) with 166Dy and studied the retention of both 166Dy and 166Ho under various conditions. Results The 166Dy was co-reduced with gold and platinum precursor to form the 166DyAu@AuNPs and 166DyPtAuNPs. The 166Dy radiolabelling efficiency was determined to be 60% and 70% for the two types of nanoparticles respectively. The retention of 166Dy and 166Ho were tested in MiliQ water or 2.5 mM DTPA for a period of 72 h. In both cases, more than 90% of both 166Dy and 166Ho was retained. The results show that the incorporation of 166Dy in AuNPs can prevent the escape of 166Ho released due to internal conversion. Conclusion We developed a chelator-free radiolabelling method for 166Dy with good radiolabelling efficiency and very high stability and retention of the daughter nuclide 166Ho. The results from this study indicate that to avoid the loss of the daughter radionuclides by internal conversion, carriers composed of electron-rich materials should be used.

With the addition of Zn2+ or Cd2+ ions, photoinduced electron transfer preferentially occurs upon photo-excitation for the forming [M:BDA-1 -H+ ]+ (M = Zn, Cd) complexes. Different from the completely suppressed radiation in the excited [Cd:BDA-1 -H+ ]+ system, fluorescence emission of the excited [Zn:BDA-1 -H+ ]+ still exhibits a considerable oscillator strength. This difference validates the zinc ion-specific fluorescence enhancement effect of BDA-1. [Display omitted] • Internal conversion suppresses the fluorescence of BDA-1 rather than photoinduced electron transfer. • Adding Zn or Cd ions causes photoinduced electron transfer in [M:BDA-1 -H+ ]+ (M = Zn, Cd) complexes upon photoexcitation. • Compared to the suppressed radiation from [Cd:BDA-1 -H+ ]+ in the S1 state, [Zn:BDA-1 -H+ ]+ has considerable oscillator strength. Ion specificity is crucial for developing fluorescence probes. Using a recently reported optical sensor (BDA-1) of Zn2+ as a representative, we carried out extensive quantum chemical calculations on its photophysical properties using density function theory. According to the calculated optimized geometries, excitation energies and transition oscillator strengths, the weak fluorescence of BDA-1 observed in experiments is attributed to the suppression of fluorescence emission by efficient internal conversion, rather than the previously proposed photoinduced electron transfer (PET) mechanism. With the addition of Zn2+ or Cd2+ ions, the tetradentate chelates [M:BDA-1 -H+ ]+ (M=Zn, Cd) are produced. According to frontier molecular orbital and interfragment charge transfer analyses of these complexes, PET is preferentially confirmed to occur upon photo-excitation. Notably, as one coordination bond in the excited [Cd:BDA-1 -H+ ]+ complex is significantly weakened in comparison to that of [Zn:BDA-1 -H+ ]+, their molecular orbital compositions in the S 1 state are completely different. As a result, absorption and radiation transitions of [Zn:BDA-1 -H+ ]+ both have considerable oscillator strength, while fluorescence radiation from the excited [Cd:BDA-1 -H+ ]+ is doubly suppressed. This difference causes that the fluorescence intensity of BDA-1 is sensitive to the addition of metal ions, and exhibits the zinc ion-specificity. [ABSTRACT FROM AUTHOR]

Increasing the spin-orbit coupling (SOC) constant by introducing heteroatoms is crucial approach for achieving efficient pure organic room-temperature phosphorescent (RTP). This research focused on the molecules 3,3″-Di(9H-carbazol-9-yl)-1,1':3′,1″-terphenyl (DCzTp) and 2,6-Bis[3-(9H-carbazol-9-yl)phenyl]pyridine (DCzPPy) using transient absorption spectroscopy experiments. For DCzTp, the femtosecond spectroscopy revealed an excited state absorption (ESA) signal at 630 nm, which reached a maximum within 1.3 ps, followed by decay of the ESA signal and appearance of triplet-triplet absorption (TTA) signal at 405 nm. An isosbestic point at 465 nm indicated the presence of intersystem crossing (ISC). In nanosecond spectroscopy, the TTA signal reached its maximum within 23 ns, and then the triplet state lifetime (τ TTA) decayed within 1.9 μs. DCzPPy exhibited faster ISC lifetime (τ ISC = 5.5 ns) and longer τ TTA (4.9 μs) compared to DCzTp. Theoretical simulations demonstrated that DCzTp transitions from the lowest singlet excited state (S 1) to the lowest triplet excited state, while DCzPPy transitions from S 1 to the higher triplet excited state (T 2). Notably, due to the heteroatom effect, the SOC constant of DCzPPy (0.27 cm−1) was greater than that of DCzTp (0.23 cm−1), leading to a faster τ ISC (5.5 ns vs. 11.4 ns). Additionally, DCzPPy exhibited an additional triplet state internal conversion process (1.1 μs), leading to a longer τ TTA (4.9 μs vs. 1.9 μs). This research provides valuable insights into how heteroatoms enhance RTP efficiency in pure organic molecules. • Photophysical processes of DCzTp and DCzPPy were detected by transient absorption spectroscopy. • DCzPPy has faster ISC process than DCzTp due to heteroatom substitution. • DCzPPy has an additional IC process, leading to a longer phosphorescence lifetime than DCzTp. [ABSTRACT FROM AUTHOR]

Using femtosecond differential spectroscopy, excitation energy transfer in reaction centers (RCs) of the carotenoidless strain of purple bacteria Rhodospirillum rubrum G9 was studied at room temperature. Excitation and probing of the Q y , Q x and Soret absorption bands of the RCs were carried out by pulses with duration of 25–30 fs. Modeling of Δ A (light – dark) kinetics made it possible to estimate the characteristic time of various stages of excitation energy transformation. It is shown that the dynamics of the downhill energy flow in the RCs is determined both by the internal energy conversion Soret→ Q x → Q y in each cofactor and by the energy transfer H* → B* → P* (H – bacteriopheophytin, B – bacteriochlorophyll a , P – bacteriochlorophyll a dimer) between cofactors. The transfer of energy between the upper excited levels (Soret and Q x) of the cofactors accelerates its arrival to the lower exciton level of the P, from where charge separation begins. It turned out that all conversion and energy transfer processes occur within 40–160 fs: the conversion Soret → Q x occurs in 40–50 fs, the conversion Q x → Q y occurs in 100–140 fs, the transfer H* → B* has a time constant of 80–120 fs, and the transfer B* → P* has a time constant of 130–160 fs. The rate of energy transfer between the upper excited levels is close to the rate of transfer between Q y levels. • Energy transfer and internal conversion make a comparable contribution to the dynamics of the downward energy flow in Rsp. rubrum G9 reaction centers. • The characteristic times of energy transfer and internal conversion are in the range of 40-160 fs. • Energy transfer between highly excited states of cofactors accelerates the dynamics of this process. • The rate of energy transfer between highly excited levels of cofactors is comparable to that for transfer between Qy levels. [ABSTRACT FROM AUTHOR]

Transient absorption dynamics of chlorophylls a and d dissolved in tetrahydrofuran was measured by the broadband femtosecond laser pump-probe spectroscopy in a spectral range from 400 to 870 nm. The absorption spectra of the excited S1 singlet states of chlorophylls a and d were recorded, and the dynamics of the of the Qy band shift of the stimulated emission (Stokes shift of fluorescence) was determined in a time range from 60 fs to 4 ps. The kinetics of the intramolecular conversion Qx→Qy (electronic transition S2→S1) was measured; the characteristic relaxation time was 54 ± 3 and 45 ± 9 fs for chlorophylls a and d, respectively. [ABSTRACT FROM AUTHOR]

Top-down ultraviolet photodissociation (UVPD) allows greater sequence coverage than any other currently available method, often fracturing the vast majority of peptide bonds in whole proteins. At the same time, UVPD can be used to dissociate noncovalent complexes assembled from multiple proteins without breaking any covalent bonds. Although the utility of these experiments is unquestioned, the mechanism underlying these seemingly contradictory results has been the subject of many discussions. Herein, some fundamental considerations of photochemistry are briefly summarized within the context of a proposed mechanism that rationalizes the experimental results obtained by UVPD. Considerations for future instrument design, in terms of wavelength choice and power, are briefly discussed. Graphical Abstract ᅟ.

• Slow internal conversion can be used for anti-dissipative solar energy conversion. • Bimolecular reactivity of high-energy MLCT states can produce high-energy species. • Polypyridines with meta topology display slow inter-ligand electron transfer. • Diimines with rigid backbones display slow hole reconfiguration. • Significant ligand backbone-solvent interactions retard internal conversion. Important fractions of the energy absorbed in natural and artificial photosynthetic schemes are dissipated via fast internal conversion processes. In contrast, chromophores that undergo internal conversion on slow timescales allow high-energy excited states to engage in bimolecular or long-range reactivity, outcompeting dissipation. This provides opportunities to improve solar energy conversion efficiencies. This review focuses on MLCT chromophores and analyzes fast and slow internal conversion processes in the form of inter-ligand electron transfer and hole reconfiguration. It discusses the current scenario, the obstacles, and the progress required to establish anti-dissipative molecular energy conversion schemes. [ABSTRACT FROM AUTHOR]

Background: Radionuclide therapy (RNT) has become a very important treatment modality for cancer nowadays. Comparing with other cancer treatment options, sufficient efficacy could be achieved in RNT with lower toxicity. β− emitters are frequently used in RNT due to the long tissue penetration depth of the β− particles. The dysprosium-166/holmium-166 (166Dy/166Ho) in vivo generator shows great potential for treating large malignancies due to the long half-life time of the mother nuclide 166Dy and the emission of high energy β− from the daughter nuclide 166Ho. However, the internal conversion occurring after β− decay from 166Dy to 166Ho could cause the release of about 72% of 166Ho when 166Dy is bound to conventional chelators. The aim of this study is to develop a nanoparticle based carrier for 166Dy/166Ho in vivo generator such that the loss of the daughter nuclide 166Ho induced by internal conversion is prevented. To achieve this goal, we radiolabelled platinum-gold bimetallic nanoparticles (PtAuNPs) and core–shell structured gold nanoparticles (AuNPs) with 166Dy and studied the retention of both 166Dy and 166Ho under various conditions. Results: The 166Dy was co-reduced with gold and platinum precursor to form the 166DyAu@AuNPs and 166DyPtAuNPs. The 166Dy radiolabelling efficiency was determined to be 60% and 70% for the two types of nanoparticles respectively. The retention of 166Dy and 166Ho were tested in MiliQ water or 2.5 mM DTPA for a period of 72 h. In both cases, more than 90% of both 166Dy and 166Ho was retained. The results show that the incorporation of 166Dy in AuNPs can prevent the escape of 166Ho released due to internal conversion. Conclusion: We developed a chelator-free radiolabelling method for 166Dy with good radiolabelling efficiency and very high stability and retention of the daughter nuclide 166Ho. The results from this study indicate that to avoid the loss of the daughter radionuclides by internal conversion, carriers composed of electron-rich materials should be used. [ABSTRACT FROM AUTHOR]

The current activities in detecting neutrinos as carriers of information from far out in our Universe prompt us to look back on the research activities a century ago that led to the discovery of these weakly interacting particles. One of the leading researchers was Lise Meitner, who observed electrons with well-defined energy, besides the continuous energy spectrum emitted in ß decay. These electron lines are well understood as radiationless nuclear transitions competing with ?-ray emission. It is proposed to name the electrons resulting out of this so-called internal conversion process after Lise Meitner and Charles D. Ellis. The equivalent process within the electronic (atomic) shell is the Auger effect, competing with X-ray emission. In this context, the radioactive decay of UX1 or 234Th, well studied a century ago by Lise Meitner and Charles Ellis, is re-visited, and the mono-energetic electrons are ascribed entirely to the internal conversion process. [ABSTRACT FROM AUTHOR]

The design and application of molecular photoswitches have attracted much attention. Herein, we performed a detailed computational study on the photoswitch benzylidene-oxazolone system based on static electronic structure calculations and on-the-fly excited-state dynamic simulations. For the Z and E isomer, we located six and four minimum energy conical intersections (MECIs) between the first excited state (S 1 ) and the ground state (S 0 ), respectively. Among them, the relaxation pathway driven by ring-puckering motion is the most competitive channel with the photoisomeization process, leading to the low photoisomerization quantum yield. In the dynamic simulations, about 88 % and 66 % trajectories decay from S 1 to S 0 for Z and E isomer, respectively, within the total simulation time of ~2 ps. The photoisomeization quantum yields obtained in our study (0.20 for Z→E and 0.12 for E→Z) agree well with the experimental measured values (0.25 and 0.11), even though the number of trajectories is limited to 50. Our study sheds light on the complexity of the benzylidene-oxazolone system 's deactivation process and the competitive mechanisms among different reaction channels, which provides theoretical guidance for further design and development of benzylidene-oxazolone based molecular photoswitches., (© 2024 The Authors. ChemPhysChem published by Wiley-VCH GmbH.)

This paper presents a unified model of gas phase acetone photophysics and photochemistry that is based on experimental data, which are reviewed and discussed in detail, and a detailed microcanonical master equation formulation. The model accounts for experimental measurements in molecular beams as well as in thermal systems, leads to a new interpretation of some experiments, and reveals a fundamental property of quantum yield measurements that are relevant to atmospheric chemistry. It also furnishes a platform for future theoretical and experimental developments. [ABSTRACT FROM AUTHOR]

Experimental triplet quantum yields of terthiophene and quaterthiophene are investigated based on the combined analysis of computed energetics, spin‐orbit coupling constants, and quantum dynamics simulations. We discuss the triplet state generation via the S1‐T3 intersystem crossing pathway. Initial Franck–Condon conditions are employed while performing the wavepacket dynamics in the triplet manifold. The wavepacket evolving on T3 state exhibits a similar electronic population decay profile in both molecules. Finally, we illustrate how the triplet quantum yield quantity depends on the two processes: the triplet state formation and its decay. [ABSTRACT FROM AUTHOR]

Ferulic acid and its derivative γ-oryzanol are common in Rice. They have the same molecular skeleton with some sunscreens that used commonly, but there were no reports on them as rice UV protection. In this work, UV absorption and fluorescence emission spectrum are performed to measure ferulic acid and γ-oryzanol effect of fighting with ultraviolet irradiation. We demonstrated that both ferulic acid and γ-oryzanol have good absorption intensity at UVA, UVB and UVC regions, with superior photostability. Furthermore, the optimized molecular conformation and potential energy surfaces (PES) in ground and excited states are obtained by using the time-dependent density functional theory (TD-DFT) method. From the calculation results, it can conclude that their S1 states decay to the S0 state via internal conversion (IC) process at the S1/S0 conical intersection (CI) point of PES followed by trans–cis photoisomerization. For the first time, we elucidated the mechanism of UV protection for ferulic acid and γ-oryzanol as UV protection in rice from our excited state non-adiabatic dynamics. [ABSTRACT FROM AUTHOR]

Cations of diamondoids and derivatives thereof have recently become the subject of experimental, spectroscopic studies due to their potential role in astrochemistry. In particular, their electronic spectra and photoinduced dynamics trigger great interest. Here, we report on computational investigations of two nitrogen-containing derivatives of the adamantane cation (Ada+, C10H16+), the amantadine cation (Ama+, C10H15NH2+) and the 1-cyanoadamantane cation (Ada-CN+, C10H15CN+). Specifically, we study electronic (vibrationally resolved) spectra and nonadiabatic molecular dynamics (modeled using the surface hopping approach based on semiempirical electronic structure theory) of these radical cations. The internal conversion time constants as well as reactive relaxation outcomes (cage-opening and hydrogen loss) are compared for the two derivatives and also with the case of Ada+ [Roy et al., Theor. Chem. Acc.2023, 142, 71]. Remarkably, we find a longer ground-state recovery time for Ada-CN+ than for Ama+ (for the same excitation energy window), despite a smaller excitation energy for the former. Thus, a static energy gap law cannot be used to rationalize nonadiabatic dynamics and excited-state lifetimes in this case: Dynamics and details of the couplings between several states play a decisive role., (© 2024 Wiley‐VCH GmbH.)

In MLCT chromophores, internal conversion (IC) in the form of hole reconfiguration pathways (HR) is a major source of dissipation of the absorbed photon energy. Therefore, it is desirable to minimize their impact in energy conversion schemes by slowing them down. According to previous findings on {Ru(bpy)} chromophores, donor-acceptor interactions between the Ru ion and the ligand scaffold might allow to control HR/IC rates. Here, a series of [Ru(tpm)(bpy)(R-py)] 2+ chromophores, where tpm is tris(1-pyrazolyl)methane, bpy is 2,2'-bipyridine and R-py is a 4-substituted pyridine, were prepared and fully characterized employing electrochemistry, spectroelectrochemistry, steady-state absorption/emission spectroscopy and electronic structure computations based on DFT/TD-DFT. Their excited-state decay was monitored using nanosecond and femtosecond transient absorption spectroscopy. HR/IC lifetimes as slow as 568 ps were obtained in DMSO at room temperature, twice as slow as in the reference species [Ru(tpm)(bpy)(NCS)] + ., (© 2024 The Authors. ChemPhysChem published by Wiley-VCH GmbH.)

In this work, the electronic excited states of hypoxanthine in solution such as water and acetonitrile are investigated by the time-dependent density functional theory (TDDFT) method. We demonstrated for the first time that the intermolecular excited-state electron transfer (ESET) from solvents to the hypoxanthine through excited-state intermolecular hydrogen-bonds cluster exhibits obvious site-selectivity. Excited-state electron transfer could only occur at the N7 site of hypoxanthine molecule in water solution, while that is the N9 site in acetonitrile. Potential energy surfaces for different electronic states of hypoxanthine with and without the influence of the excited-state hydrogen bonding cluster are also discussed. Site-selective ESET is proposed to induce the internal conversion of hypoxanthine from S2 state to S1 at a conical intersection, which is responsible for the ultrashort lifetime of hypoxanthine in excited state in solution. These results pave a novel way to understand the photophysical and photochemical behaviors of DNA bases and their derivatives in solution phase. [ABSTRACT FROM AUTHOR]

[Display omitted] • Modifying C 60 using threonine decreases the excitation degeneration and redshifts low-lying and excited states. • Calculated ISC rate constants for S 1 → T 1 transitions indicate a fairly effective process of saturation the triplet state. • Calculated IC rate constants for S 1 → S 0 two orders of magnitude less than for ISC marking that IC cannot compete with ISC. • The main source of the IC process is the anharmonic C-H vibrations of hydrogens bound to fullerene. DFT calculations showed that disruption of the π network of the fullerene due to the addition of up to four threonines does not affect the efficiency of saturation of the T 1 state by intersystem crossing compared to pure C 60. Internal conversion from S 1 to the ground state does not compete with intersystem crossing to T 1 state. The regulating of C-H vibrations associated with hydrogens bound to fullerene may govern the quantum yield of the triplet state saturation. Resulting phosphorescence lifetimes high enough to guarantee a high probability of quenching the triplet state by molecular oxygen. [ABSTRACT FROM AUTHOR]

Singlet fission (SF) holds the potential to boost the maximum power conversion efficiency of photovoltaic devices. Internal conversion (IC) has been considered as one of the major competitive deactivation pathways to transform excitation energy into heat. Now, using time‐resolved spectroscopy and theoretical calculation, it is demonstrated that, instead of a conventional IC pathway, an unexpected intramolecular singlet fission (iSF) process is responsible for excited state deactivation in isoindigo derivatives. The 1TT state could form at ultrafast rate and nearly quantitatively in solution. In solid films, the slipped stacked intermolecular packing of a thiophene‐functionalized derivative leads to efficient triplet pair separation, giving rise to an overall triplet yield of 181 %. This work not only enriches the pool of iSF‐capable materials, but also contributes to a better understanding of the iSF mechanism, which could be relevant for designing new SF sensitizers. [ABSTRACT FROM AUTHOR]