A time resolved double pump–probe experimental technique to characterize excited-state parameters of organic dyes
46
Citation
10
Reference
10
Related Paper
Citation Trend
Abstract:
We report a novel time resolved double pump–probe experimental technique that may be used to characterize the excited-state parameters of organic dyes. We show that by monitoring the time evolution of the transmittance of a dye after excitation with two pump pulses, the excited singlet and triplet absorption cross sections, the lifetime of the excited singlet state, and the triplet quantum yield may all be measured. This technique has been demonstrated for silicon 2,3-naphthalocyanine bis(trihexylsiloxide).Keywords:
Singlet fission
Quantum yield
Cite
Singlet fission
Pentacene
Annihilation
Acene
Exothermic reaction
Cite
Citations (68)
A recent computational investigation of Jahn−Teller effects in unsaturated 16-electron d4d6 [CpMLn] complexes (Abu-Hasanayn, F.; Cheong, P.; Oliff, M. Angew. Chem. 2002, 41, 2120) highlighted the typical presence of two spin-triplet and two singlet states of competing stability in these complexes and pointed out the necessity to account for more than one electronic state in studies thereof. Consequently, we have reinvestigated the addition of N2 to all the four low-energy states of CpMoCl(PH3)2, a reaction for which previously only one singlet and one triplet state have been considered (Keogh, D. W.; Poli, R. J. Am. Chem. Soc. 1997, 119, 2516). The present study was performed using density functional theory (DFT) and the thus obtained relative stabilities of the four electronic states of the educt are in good accord with those obtained using a multireference MP2 method. The spin-singlet ground state of the 18e- product of N2 addition turns out to be derived from the fourth lowest state (21A') of the 16e- educt, immediately demonstrating the importance of accounting for more than one triplet and one singlet state in such reactions. The barrier to N2 addition was found to arise from the enthalpic cost of obtaining identical geometries for this singlet state and the spin-triplet ground state of the educt (3A' ') in the minimum energy crossing point (MECP). With a spin-triplet ground-state reactant complex, a triplet−singlet MECP defining the rate-limiting step, and a singlet product, our calculated activation (14.4 kcal/mol) as well as reaction enthalpies (21.2 kcal/mol) of N2 addition to CpMoCl(PMe3)2 are found to be within the experimental error bars of those measured for Cp*MoCl(PMe3)2. For the corresponding reaction with CO, there is a delicate balance between the transition state (TS) of addition on the triplet potential energy surface (PES) and the point of crossing between the triplet and singlet PES. Our optimized TS and MECPs for this reaction suggest that the rate is controlled by the barrier defined by the spin-triplet TS, with spin inversion occurring after this point. Our calculated activation enthalpy (6.7 kcal/mol) based on the spin-triplet TS is in excellent agreement with that measured for Cp*MoCl(PMe3)2.
Cite
Citations (15)
Coupled cluster
Singlet fission
Basis (linear algebra)
Cite
Citations (45)
Singlet fission
Cite
Citations (0)
The photophysical processes of singlet fission and triplet fusion have numerous emerging applications. They respectively involve the separation of a photo-generated singlet exciton into two dark triplet excitons and the fusion of two dark triplet excitons into an emissive singlet exciton. The role of the excimer state, and the nature of the triplet-pair state in these processes have been a matter of contention. Here we carefully analyse the room temaperature time-resolved emission of a neat liquid singlet fission chromophore, 5,12-bis(n-octyldiisopropylsilylethynyl)tetracene. It is demonstrated to exhibit three spectral components: Two that correspond to the bright singlet and excimer states, and a third component that becomes more prominent during triplet fusion. A spectrum consistent with this third compoment is found to be enhanced with magnetic fields, confirming its origins in radiation from weakly-coupled triplet pairs. This magnetically enhanced emission is attributed to the emission from the strongly coupled triplet pair state. These observations serve to unite the view that there is an emissive intermediate in singlet fission and triplet fusion, and that this species is distinct from the broad, unstructured excimer emission.
Singlet fission
Excimer
Tetracene
Chromophore
Cite
Citations (2)
The authors have previously proposed a theoretical model for exotic spin alignment in organic molecular assemblages: The alternating chain of organic biradicals in a singlet (Sb = 0) ground state and monoradicals with S = 1/2 has a ferrimagnetic ground state for the whole chain, which has been termed generalized ferrimagnetism. An important feature of the generalized ferrimagnetic spin alignment has been found in the deviation of the expectation value 〈Sb2〉 of the biradical spin from zero. Even a triplet-like spin state 〈Sb2〉 = 2 (Sb = 1) has been predicted in the theoretical calculations. In this study, we have found experimental evidence for the pseudo-triplet state appearing in the ground-state singlet biradical of a real open-shell compound. At first, we have demonstrated from theoretical calculations that the singlet biradical has 〈Sb2〉 = 2 (Sb = 1) in a molecular pair with an S = 1 metal ion as well as with the S = 1/2 monoradical. The pseudo-triplet state of the biradical affords a singlet state of the whole system of the biradical-metal ion pair, which is readily detectable in experiments for verifying the theoretical prediction. As a model compound for the biradical-metal ion pair, a transition metal complex, [(bnn)(Ni(hfac)2)1.5(H2O)] (1), has been synthesized from a nitronyl nitroxide-based ground-state singlet biradical bnn and Ni(hfac)2. From X-ray crystallographic analyses, the compound contains a molecular pair of bnn and Ni(hfac)2, which serves as a model system under the above theoretical studies. It has been found from the analysis of the temperature dependence of magnetic susceptibility that the bnn−Ni(hfac)2 pair has the singlet (S = 0) ground state. The singlet ground state of the pair results from an antiparallel coupling of the pseudo-triplet of the biradical and the S = 1 spin on the Ni ion. The pseudo-triplet state in the ground-state singlet biradical has thus been verified experimentally, which is crucially important to realize the generalized ferrimagnetic spin alignment.
Ferrimagnetism
Diradical
Spin states
Cite
Citations (5)
The Equilibrium geometrical optimizations on OCS linear and nonlinear molecules in the singlet and triplet states have been made using density functional theory B3LYP method with 6-31l++G~(**)and aug-CC-pVTZ basis sets.The ground state is ~1∑with linear C_(∞v) symmetry The linear and nonlinear structures in singlet state can be stable,and there is only nonlinear stablestructure in triplet state.
Singlet fission
Basis (linear algebra)
Cite
Citations (0)
Quantum yield
Hexane
Cite
Citations (12)
Extensive density functional calculations were used to explore the geometries and relative stabilities of metallabenzenes with various spin multiplicities. The structural modification effects on the energy splittings between the singlet and triplet states, including the replacement of metal, the change of ligand environment, and the substitution of hydrogen and carbon atoms in the aromatic ring, were investigated. Calculations show that the stability of the singlet and triplet metallabenzenes strongly depends on the metal center, and the first-row transition metal metallabenzenes most probably have the triplet ground state. The stability of the triplet state can be enhanced by the strong π- and weak-field ligands as well as the electron-withdrawing substituent for hydrogen at the aromatic carbon such as - PPh 3+ . Present results can help us understand the magnetic properties of metallabenzenes and construct the function-orientated metallacyclic compounds.
Spin states
Polar effect
Cite
Citations (7)
We report the first theoretical calculations of excited state absorptions (ESAs) from the singlet and triplet excitons, as well as the key intermediate in the singlet fission (SF) process, the spin singlet multiexciton triplet-triplet state, for solid pentacene with herringbone crystal structure. Our goal is to compare theoretical results against ultrafast transient photoinduced absorption (PA) measurements and their interpretations, which have remained controversial. We show that the elusive triplet-triplet state absorbs both in the visible and near infrared (NIR), at or close to the PA energies assigned to the free triplet exciton. In contrast, the triplet PA has nearly vanishing oscillator strength in the NIR within the rigid herringbone structure. Observable oscillator strength for NIR triplet PA requires photoinduced enhancement of coupling between a pair of neighboring pentacene molecules that confers significant charge-transfer (CT) character to the triplet exciton. We discuss the implication of our results for efficient SF in pentacene and related materials.
Singlet fission
Pentacene
Oscillator strength
Cite
Citations (5)