The dependence of singlet exciton relaxation on excitation density and temperature in polycrystalline tetracene thin films: Kinetic evidence for a dark intermediate state and implications for singlet fission

Burdett, Jonathan J.; Gosztola, David; Bardeen, Christopher J.

doi:doi:10.1063/1.3664630

Volume/Page
Keyword
DOI
Citation
Advanced

Volume: Page/Article:

Search Content Type

article doi:

Citation:

Thermal properties of ionic systems near the liquid-liquid critical point

Isobaric heat capacity per unit volume, Cp, and excess molar enthalpy, hE, were determined in the vicinity of the critical point for a set of binary systems formed by an ionic liquid and a molecular solvent. Moreover, and, since critical composition had to be accurately determined, liquid-liquid equilibrium curves were also obtained using a calorimetric method. The systems were selected with a view on representing, near room temperature, examples from clearly solvophobic to clearly coulombic beh...

Vibrational dynamics of the bending mode of water interacting with ions

We studied the vibrational relaxation dynamics of the bending mode (ν2) of the H2O water molecules in the presence of different salts (LiCl, LiBr, LiI, NaI, CsI, NaClO4, and NaBF4). The linear and nonlinear spectra of the bending mode show distinct responses of water molecules hydrating the anions. We observe that the bending mode of water molecules that are hydrogen-bonded to an anion exhibits much slower relaxation rates (T1 ∼ 1ps) than water molecules that are hydrogen-bonded to other water m...

The excited state dynamics of polycrystalline tetracene films are studied using femtosecond transient absorption in combination with picosecond fluorescence, continuing work reported in an earlier paper [J. J. Burdett, A. M. Muller, D. Gosztola, and C. J. Bardeen, J. Chem. Phys. 133, 144506 (2010)]. A study of the intensity dependence of the singlet state decay is conducted to understand the origins of the discrepancy between the broadband transient absorption and fluorescence experiments seen previously. High-sensitivity single channel transient absorption experiments allow us to compare the transient absorption dynamics to the fluorescence dynamics measured at identical laser fluences. At high excitation densities, an exciton-exciton annihilation rate constant of ∼1 × 10⁻⁸ cm³ s⁻¹ leads to rapid singlet decays, but at excitation densities of 2 × 10¹⁷ cm⁻³ or less the kinetics of the transient absorption match those of the fluorescence. At these lower excitation densities, both measurements confirm that the initially excited singlet state relaxes with a decay time of 80 ± 3 ps, not 9.2 ps as claimed in the earlier paper. In order to investigate the origin of the singlet decay, the wavelength-resolved fluorescence dynamics were measured at 298 K, 77 K, and 4 K. A high-energy J-type emitting species undergo a rapid (∼100 ps) decay at all temperatures, while at 77 K and 4 K additional species with H-type and J-type emission lineshapes have much longer lifetimes. A global analysis of the wavelength-dependent decays shows that the initial ∼100 ps decay occurs to a dark state and not via energy transfer to lower energy bright states. Varying the excitation wavelength from 400 nm to 510 nm had no effect on the fast decay, suggesting that there is no energy threshold for the initial singlet relaxation. The presence of different emitting species at different temperatures means that earlier interpretations of the fluorescence behavior in terms of one singlet state that is short-lived due to singlet fission at high temperatures but long-lived at lower temperatures are probably too simplistic. The presence of a rapid singlet decay at all temperatures indicates that the initially created J-type singlet exciton decays to an intermediate that only produces free triplets (and delayed fluorescence) at high temperatures.

Article Outline

INTRODUCTION
EXPERIMENTAL
RESULTS AND DISCUSSION
CONCLUSIONS

RELATED DATABASES

To view database links for this article, you need to log in.

KEYWORDS and PACS

Keywords

excitons, fluorescence, high-speed optical techniques, organic compounds, thin films

PACS

71.35.-y

Excitons and related phenomena
78.66.Qn

Polymers; organic compounds
78.55.Kz

Solid organic materials
78.47.jb

Transient absorption

ARTICLE DATA

Digital Object Identifier

http://dx.doi.org/10.1063/1.3664630

PUBLICATION DATA

ISSN

0021-9606 (print)

1089-7690 (online)

Publisher

$abstract.society.value is a Member of CrossRef

American Institute of Physics

Figures (9) Tables (1)

Access to article objects (figures, tables, multimedia) requires a subscription; log in to view available files.
(Access to supplementary files, where available, is free for this journal.)