Recalling the appropriate representation of electronic spectra

Angulo, Gonzalo; Grampp, Güenter; Rosspeintner, Arnulf

doi:10.1016/j.saa.2006.01.007

Cited by 121 publications

(125 citation statements)

References 6 publications

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“…This correction by the photon energy dependence is derived from the Einstein coefficients of absorption and spontaneous emission, and it is described in detail elsewhere. 67 In this representation, the spectral intensity is directly proportional to the squared magnitude of the transition dipole moment (TDM) and as a consequence to the Franck−Condon factor. Note that the emission spectra in solution are cut below 12 500 cm −1 (800 nm) because of experimental limitations of the fluorimeter.…”

Section: Methodsmentioning

confidence: 99%

Breaking Down the Problem: Optical Transitions, Electronic Structure, and Photoconductivity in Conjugated Polymer PCDTBT and in Its Separate Building Blocks

et al. 2012

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Conjugated polymers with alternating electronwithdrawing and electron-donating groups along their backbone (donor−acceptor copolymers) have recently attracted attention due to high power conversion efficiency in bulk heterojunction solar cells. In an effort to understand how the bandgap in a typical donor−acceptor copolymer is reduced by internal charge transfer character and what the implications of this charge transfer are, we have synthesized the isolated repeat unit (CDTBT) of the photovoltaically highly successful PCDTBT polymer. We compare here the spectroscopic and electrochemical properties of the polymer, the repeat unit, and the separate carbazole donor and dithienylbenzothiadiazole acceptor moieties (CB and dTBT, respectively) in the solid state and in solutions of various polarity. The results are interpreted with the help of time-dependent density functional theory (TD-DFT) calculations. We identify the dominant electronic transitions responsible for the first two absorption bands in the "camel back" spectrum of PCDTBT as partial charge transfer transitions with significant delocalization in the directly excited states. The low bandgap, overall shape, and partial charge transfer character of the PCDTBT absorption spectrum originate from transitions in the dTBT unit. The attached CB moiety extends the conjugation length in CDTBT, rather than acting as a localized donor. Further electronic delocalization, leading to a relatively small reduction in bandgap, occurs upon polymerization. We use our finding of higher delocalization following excitation in the second absorption band to explain the increased yield of photogenerated charges from this band in PCDTBT solid thin films. Moreover, we point out the importance of initial delocalization in the functioning of bulk heterojunction solar cells. The results presented here are therefore not only highly important for a better understanding of donor−acceptor copolymers in general but can also potentially guide the strategic development of future photovoltaic materials.

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Section: Methodsmentioning

confidence: 99%

Breaking Down the Problem: Optical Transitions, Electronic Structure, and Photoconductivity in Conjugated Polymer PCDTBT and in Its Separate Building Blocks

et al. 2012

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“…The fluorescence spectrum was corrected for the instrument response and multiplied by a factor of l 4 to obtain the spectral shape of the stimulated emission in the time resolved absorption spectra. 41 …”

Section: Methodsmentioning

confidence: 99%

Unraveling the flavin-catalyzed photooxidation of benzylic alcohol with transient absorption spectroscopy from sub-pico- to microseconds

Megerle

Wenninger

Kutta

et al. 2011

Phys. Chem. Chem. Phys.

102

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Flavin-mediated photooxidations have been described for applications in synthetic organic chemistry for some time and are claimed to be a route to the use of solar energy. We present a detailed investigation of the involved photophysical and photochemical steps in methoxybenzyl alcohol oxidation on a timescale ranging from sub-picoseconds to tens of microseconds. The results establish the flavin triplet state as the key intermediate for the photooxidation. The initial step is an electron transfer from the alcohol to the triplet state of the flavin catalyst with, followed by a proton transfer in B6 ms. In contrast, the electron transfer involving the singlet state of flavin is a loss channel. It is followed by rapid charge recombination (t = 50 ps) without significant product formation as seen when flavin is dissolved in pure benzylic alcohol. In dilute acetonitrile/water solutions of flavin and alcohol the electron transfer is mostly controlled by diffusion, though at high substrate concentrations >100 mM we also find a considerable contribution from preassociated flavin-alcohol-aggregates. The model including a productive triplet channel and a competing singlet loss channel is confirmed by the course of the photooxidation quantum yield as a function of substrate concentration: We find a maximum quantum yield of 3% at 25 mM of benzylic alcohol and significantly smaller values for both higher and lower alcohol concentrations. The observations indicate the importance to perform flavin photooxidations at optimized substrate concentrations to achieve high quantum efficiencies and provide directions for the design of flavin photocatalysts with improved performance.

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“…10.0 10 3 cm À1 ), implying that the interactionb etween The spectraare plotted in the wavenumber representation, [58] but the wavelengths cale is showno n the top axis for comparison. 10.0 10 3 cm À1 ), implying that the interactionb etween The spectraare plotted in the wavenumber representation, [58] but the wavelengths cale is showno n the top axis for comparison.…”

Section: Steady-state Absorption and Emissionmentioning

confidence: 99%

“…. The spectraare plotted in the wavenumber representation, [58] but the wavelengths cale is showno n the top axis for comparison. Table 1.…”

Section: Steady-state Absorption and Emissionmentioning

confidence: 99%

Untying the Photophysics of Quinolinium‐Based Molecular Knots and Links

Caprice

Aster

Kumpulainen

2020

Chemistry A European J

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Complex molecular knots and links are still difficult to synthesize and the properties arising from their topology are mostly unknown. Here, we report on ac omparativep hotophysical study carried out on af amily of closely related quinolinium-based knots and links to determine the impact exertedby topology on the molecularb ackbone. Our results indicatet hat topology has an egligible influence on the behavior of loosely braided molecules, which mostly behave like their unbraided equivalents. On the other hand, tightly braided molecules display distinct features. Their higher packing density results in ap ronounceda bility to resist deformation,asignificant reduction in the solvent-accessible surface area and favors close-range p-p interactions betweent he quinolinium units and neighboring aromatics. Finally,t he sharp alteration in behavior between looselya nd tightly braided molecules sheds light on the factorsc ontributingt ob raiding tightness.

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Recalling the appropriate representation of electronic spectra

Cited by 121 publications

References 6 publications

Breaking Down the Problem: Optical Transitions, Electronic Structure, and Photoconductivity in Conjugated Polymer PCDTBT and in Its Separate Building Blocks

Breaking Down the Problem: Optical Transitions, Electronic Structure, and Photoconductivity in Conjugated Polymer PCDTBT and in Its Separate Building Blocks

Unraveling the flavin-catalyzed photooxidation of benzylic alcohol with transient absorption spectroscopy from sub-pico- to microseconds

Untying the Photophysics of Quinolinium‐Based Molecular Knots and Links

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