Vibronic coupling in J-aggregates and beyond: a direct means of determining the exciton coherence length from the photoluminescence spectrum

Frank C Spano, Hajime Yamagata
Journal of Physical Chemistry. B 2011 May 12, 115 (18): 5133-43
Exciton coherence in a J-aggregate with exciton−phonon coupling involving a single intramolecular vibration is studied. For linear aggregates with no disorder and periodic boundary conditions, the 0−0 to 0−1 line strength ratio, S(R), corresponding to the low-temperature photoluminescence spectrum is rigorously equal to N/λ2, where N is the number of chromophores comprising the aggregate and λ2 is the Huang−Rhys factor of the coupled vibrational mode. The result is independent of exciton bandwidth and therefore remains exact from the weak to strong exciton−phonon coupling regimes. The simple relation between S(R) and N also holds for more complex morphologies, as long as the transition from the lowest exciton state to the vibrationless ground state is symmetry-allowed. For example, in herringbone aggregates with monoclinic unit cells, the line strength ratio, defined as SR ≡ I(b)(0−0)/I(b)(0−1) (where I(b)(0−0) and I(b)(0−1) correspond to the b-polarized 0−0 and 0−1 line strengths, respectively) is rigorously equal to N/λ2. In the presence of disorder and for T > 0 K, λ2S(R) is closely approximated by the exciton coherence number N(coh), thereby providing a simple and direct way of extracting N(coh) from the photoluminescence spectrum. Increasing temperature in linear J-aggregates (and herringbone aggregates) generally leads to a demise in S(R) and therefore also the exciton coherence size. When no disorder is present, and under the fast scattering and thermodynamic limits, S(R) is equal to N(T)/λ2, where the thermal coherence size is given by N(T) = 1 + [4πω(c)/k(b)T](d/2) for an aggregate of dimension d, where ω(c) is the exciton band curvature at k = 0.

Full Text Links

Find Full Text Links for this Article


You are not logged in. Sign Up or Log In to join the discussion.

Related Papers

Remove bar
Read by QxMD icon Read

Search Tips

Use Boolean operators: AND/OR

diabetic AND foot
diabetes OR diabetic

Exclude a word using the 'minus' sign

Virchow -triad

Use Parentheses

water AND (cup OR glass)

Add an asterisk (*) at end of a word to include word stems

Neuro* will search for Neurology, Neuroscientist, Neurological, and so on

Use quotes to search for an exact phrase

"primary prevention of cancer"
(heart or cardiac or cardio*) AND arrest -"American Heart Association"