Effect of temperature on symmetry breaking excited state charge separation: restoration of symmetry at elevated temperature

Khandelwal, Hitesh; Mallia, Ajith R.; Cheriya, Rijo T.; Hariharan, Mahesh

doi:10.1039/c2cp42452e

Cited by 21 publications

(36 citation statements)

References 29 publications

(34 reference statements)

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“…This is why the decline of the fluorescence yield and no appearance of ISC process in THHBI-PhNPh 2 . This process could be more remarkable with the increase of the solvent polarity 11 31 53 .…”

Section: Resultsmentioning

confidence: 94%

Ultrafast Investigation of Intramolecular Charge Transfer and Solvation Dynamics of Tetrahydro[5]-helicene-Based Imide Derivatives

Zhu

et al. 2016

Sci Rep

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We report the excited-state intramolecular charge transfer (ICT) characteristics of four tetrahydro[5] helicene-based imide (THHBI) derivatives with various electron-donating substitutes in different polarity of solvents using steady-state, time-resolved transient absorption (TA) spectroscopy. It is found that, the small bathochromic-shift of the absorption spectra but large red shift of the emission spectra for all dyes with increasing solvent polarity indicates the larger dipole moment of the excited state compared to ground state. The results of theoretical calculations exhibit the charge transfer from the terminal donors to helical backbone, which accounts for the degrees of red shift of the emission spectra from different extent of ICT nature. Time-resolved TA spectra recorded as a function of electron-donating substitutes and solvent polarity show the dye with stronger donors (THHBI-PhNPh2) in more polar solvent behaves faster excited-state ICT relaxation, leading to the formation of solvent-stabilized ICT state (ICT’ state) from the excited ICT state; The dyes (THHBI-Ph, THHBI-PhCF3 and THHBI-PhOMe) with relative weaker donors show weaker dependence on solvent polarity, and instead of that intersystem crossing (ISC) becomes possible from ICT state to triplet state.

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Section: Resultsmentioning

confidence: 94%

Ultrafast Investigation of Intramolecular Charge Transfer and Solvation Dynamics of Tetrahydro[5]-helicene-Based Imide Derivatives

Zhu

et al. 2016

Sci Rep

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“…This state most likely has CT character and is formed via a symmetry-breaking mechanism similar to that which occurs in other bichromophoric systems. 23,33,62−64 Further support for the hypothesis that the observed photophysical properties of zDIP1–zDIP4 are associated with SBCT is the weaker dependence on solvent polarity for the heteroleptic complexes zDIP2′ and zDIP3′, where SBCT is impossible.…”

Section: Results and Discussionmentioning

confidence: 95%

Symmetry-Breaking Charge Transfer of Visible Light Absorbing Systems: Zinc Dipyrrins

et al. 2014

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Zinc dipyrrin complexes with two identical dipyrrin ligands absorb strongly at 450–550 nm and exhibit high fluorescence quantum yields in nonpolar solvents (e.g., 0.16–0.66 in cyclohexane) and weak to nonexistent emission in polar solvents (i.e., <10–3, in acetonitrile). The low quantum efficiencies in polar solvents are attributed to the formation of a nonemissive symmetry-breaking charge transfer (SBCT) state, which is not formed in nonpolar solvents. Analysis using ultrafast spectroscopy shows that in polar solvents the singlet excited state relaxes to the SBCT state in 1.0–5.5 ps and then decays via recombination to the triplet or ground states in 0.9–3.3 ns. In the weakly polar solvent toluene, the equilibrium between a localized excited state and the charge transfer state is established in 11–22 ps.

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“…Our continued interest towards the design of near-orthogonally arranged D-A systems, for exploiting favorable photo-processes in isolated 19 and organized environment, 20 enabled us to restrict the co-facial arrangement 21 of electronically complementary aromatic chromophorScheme 1. Representative strategies adopted to spatially organize electron donors and acceptors for emergent properties.…”

Section: Non-parallel Stacks Of Donor and Acceptor Chromophores Evadementioning

confidence: 99%

Nonparallel Stacks of Donor and Acceptor Chromophores Evade Geminate Charge Recombination

2015

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We report a nonparallel stacked arrangement of donor–acceptor (D–A) pairs for prolonging the lifetime of photoinduced charge-separated states. Hydrogen–hydrogen steric repulsion in naphthalimide-naphthalene (NIN) dyad destabilizes the planar geometry between the constituent units in solution/ground state. Sterically imposed nonplanar geometry of the dyad allows the access of nonparallel arrangement of the donor and acceptor stacks having triclinic space group in the crystalline state. Antiparallel trajectory of excitons in nonparallel D–A stacks can result in lower probability of geminate charge recombination, upon photoexcitation, thereby resulting in a long-lived charge-separated state. Upon photoexcitation of the NIN dyad, electron transfer from naphthalene to the singlet excited state of naphthalimide moiety results in radical ion pair intermediates that survive >10,000-fold longer in the aggregated state (τcra > 1.2 ns) as compared to that of monomeric dyad (τcrm < 110 fs), monitored using femtosecond transient absorption spectroscopy.

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Effect of temperature on symmetry breaking excited state charge separation: restoration of symmetry at elevated temperature

Cited by 21 publications

References 29 publications

Ultrafast Investigation of Intramolecular Charge Transfer and Solvation Dynamics of Tetrahydro[5]-helicene-Based Imide Derivatives

Ultrafast Investigation of Intramolecular Charge Transfer and Solvation Dynamics of Tetrahydro[5]-helicene-Based Imide Derivatives

Symmetry-Breaking Charge Transfer of Visible Light Absorbing Systems: Zinc Dipyrrins

Nonparallel Stacks of Donor and Acceptor Chromophores Evade Geminate Charge Recombination

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