The triplet state in trans → cis‐photoisomerization of thioindigo

Karstens, Ties; Kobs, K.; Memming, R.

doi:10.1002/bbpc.19790830511

Cited by 25 publications

(5 citation statements)

References 15 publications

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“…It can be seen that for TI , besides the intense transient maxima at 580 nm, a depletion band is obtained at 540 nm (matching the visible absorption band in Figure ). The transient signals were identified as triplets since they were quenched by oxygen with diffusion-controlled rate constants (∼10 9 M –1 s –1 , see Experimental section); moreover, the transient with maxima at 580 nm matches those previously reported for TI triplets − (with values ranging from 575 to 600 nm depending on solvent and substitution on TI ). Others have also obtained a triplet signal for TI in dichloromethane solution with k q = 3.2 × 10 9 M –1 s –1 and a lifetime of 158 ns (279 ns in benzene), which again corroborates our values: k q = 2.1 × 10 9 M –1 s –1 and τ T = 389 ns in Table .…”

Section: Resultssupporting

confidence: 72%

Thio-Mayan-like Compounds: Excited State Characterization of Indigo Sulfur Derivatives in Solution and Incorporated in Palygorskite and Sepiolite Clays

Rondão

Melo

2012

J. Phys. Chem. C

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Following what may mirror the recipe used by the ancient Maya civilization, consisting of a mixture of indigo and palygorskite, leading to the organic/inorganic pigment known as Maya Blue, we have switched indigo with thioindigo (TI) and a derivative (Ciba Brilliant Pink, CBP) and synthesized what was Christianized as "Maya Pink". The spectral and photophysical behavior of TI and CBP was investigated in solution and solid state (in powder and incorporated in palygorskite clays). In solution, TI was investigated in different organic solvents (benzene, toluene, and dioxane) at room and low temperatures and further compared with indigo. TI displays a different spectral and photophysical behavior when compared to indigo: fluorescence dominating the deactivation of the first excited singlet state (50−70% depending on the solvent), with the S 1 -→S 0 internal conversion and the S 1 -→T 1 intersystem crossing deactivation channels representing the remaining quanta loss. Moreover, whereas in the case of indigo the proton transfer process in the excited state (between the N−H and CO groups), involving the formation of two excited species, leads to an efficient internal conversion radiationless process, with TI this process is precluded leading to a single exponential fluorescence decay. Incorporation of TI and CBP in palygorskite and sepiolite clays has showed different photophysical properties with decrease of the fluorescence quantum yields, a single exponential decay for TI and a multiexponential decay for CBP in palygorskite. Based on molecular fluorescence data, potential locations of TI and CBP in the clay are equated.

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Section: Resultssupporting

confidence: 72%

Thio-Mayan-like Compounds: Excited State Characterization of Indigo Sulfur Derivatives in Solution and Incorporated in Palygorskite and Sepiolite Clays

Rondão

Melo

2012

J. Phys. Chem. C

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“…Most studies on isoindigo chromophores have focused on singlet excited state properties; as such, the triplet excited state of this versatile acceptor remains unexplored to date. By contrast, the triplet excited state properties of indigo and thioindigo dyes were explored several decades ago. − One approach to enhancing the efficiency for formation of the triplet excited state is to incorporate heavy metals into a π-conjugated electronic system to induce spin–orbit coupling (SOC) and enhance singlet–triplet intersystem crossing (ISC). Considering the importance of triplet excited states in optoelectronics, it is necessary to explore the triplet excited state properties of isoindigo based chromophores.…”

Section: Introductionmentioning

confidence: 99%

π-Conjugated Organometallic Isoindigo Oligomer and Polymer Chromophores: Singlet and Triplet Excited State Dynamics and Application in Polymer Solar Cells

Goswami

Gish

Wang

et al. 2015

ACS Appl. Mater. Interfaces

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An isoindigo based π-conjugated oligomer and polymer that contain cyclometalated platinum(II) "auxochrome" units were subjected to photophysical characterization, and application of the polymer in bulk heterojunction polymer solar cells with PCBM acceptor was examined. The objective of the study was to explore the effect of the heavy metal centers on the excited state properties, in particular, intersystem crossing to a triplet (exciton) state, and further how this would influence the performance of the organometallic polymer in solar cells. The materials were characterized by electrochemistry, ground state absorption, emission, and picosecond-nanosecond transient absorption spectroscopy. Electrochemical measurements indicate that the cyclometalated units have a significant impact on the HOMO energy level of the chromophores, but little effect on the LUMO, which is consistent with localization of the LUMO on the isoindigo acceptor unit. Picosecond-nanosecond transient absorption spectroscopy reveals a transient with ∼100 ns lifetime that is assigned to a triplet excited state that is produced by intersystem crossing from a singlet state on a time scale of ∼130 ps. This is the first time that a triplet state has been observed for isoindigo π-conjugated chromophores. The performance of the polymer in bulk heterojunction solar cells was explored with PC61BM as an acceptor. The performance of the cells was optimum at a relatively high PCBM loading (1:6, polymer:PCBM), but the overall efficiency was relatively low with power conversion efficiency (PCE) of 0.22%. Atomic force microscopy of blend films reveals that the length scale of the phase separation decreases with increasing PCBM content, suggesting a reason for the increase in PCE with acceptor loading. Energetic considerations show that the triplet state in the polymer is too low in energy to undergo charge separation with PCBM. Further, due to the relatively low LUMO energy of the polymer, charge transfer from the singlet to PCBM is only weakly exothermic, which is believed to be the reason that the photocurrent efficiency is relatively low.

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“…Both possible phenomena increase drastically the intersystem crossing rate already on the initial stage of the rotation. [4][5][6] This picture of the preferential cis intersystem crossing differs somewhat from that of the model of Memming et al 7,s where the possibility of the large rotation angles in the $1 (cis) state is assumed. lrans c s FIGURE 5 The proposed scheme of trans cis photoisomerization of thioindigoid dyes.…”

Section: Picosecond Thioindigoid Isomerizationmentioning

confidence: 64%

“…The common point of view on the mechanism of thioindigoid dyes photoisomerization is absent at present. An involvement of the trans isomer triplet state in the trans--cis photoisomerization was established [1][2][3][4] by nanosecond absorption spectroscopy. The results of the fluorescence studies, 5'6 were interpreted on the other hand in terms of photoisomerization in the singlet state of the trans isomer.…”

Section: Introductionmentioning

confidence: 99%

Picosecond Laser Study of Thioindigoid Dyes Photoisomerization

Krysanov

Алфимов

1983

Laser Chemistry

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The transient species in the trans ⇌ cis photoisomerization of the perinaphto–thioindigoid dye were identified by picosecond laser spectroscopy in the time domain 10 ps–5 ns. An excitation of the trans isomer with a 6 ps, 528 nm pulse to the singlet state S1 (the peak of S′n ← S1 absorption at 700 nm) results in the intersystem crossing S1 ⇝ T1 (the peak of Tn ← T1 absorption at 730 nm) with the quantum yield of 0.7 and rate constant (1.4 ± 0.3)· 109s−1. An excitation of the cis isomer results also in the intersystem crossing (the peak of Tn> ← T1 absorption at 670 nm) with the rate constant (3.7 ± 1.2)· 1010s−1. The triplet mechanism of the photoisomerization in the both directions is proposed.

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The triplet state in trans → cis‐photoisomerization of thioindigo

Cited by 25 publications

References 15 publications

Thio-Mayan-like Compounds: Excited State Characterization of Indigo Sulfur Derivatives in Solution and Incorporated in Palygorskite and Sepiolite Clays

Thio-Mayan-like Compounds: Excited State Characterization of Indigo Sulfur Derivatives in Solution and Incorporated in Palygorskite and Sepiolite Clays

π-Conjugated Organometallic Isoindigo Oligomer and Polymer Chromophores: Singlet and Triplet Excited State Dynamics and Application in Polymer Solar Cells

Picosecond Laser Study of Thioindigoid Dyes Photoisomerization

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