Abstract
The coherence length of the Frenkel excitons (N(coh)) is one of the most critical parameters governing many key features of supramolecular J-aggregates. Determining experimentally the value of N(coh) is a nontrivial task since it is sensitive to the technique/method applied, causing discrepancies in the literature data even for the same chemical compound and aggregation conditions. By using a combination of different experimental techniques including UV-vis-NIR, fluorescence emission, time-resolved photoluminescence, and transient absorption spectroscopies, we determined N(coh) values for J-aggregates of a cyanine dye. We found that the absorption spectroscopy alone - a widely used technique- fails in determining right value for N(coh). The correct approach is based on the modification of photoluminescence lifetime and nonlinear response upon aggregation and careful analysis of the Stokes shift and electron-phonon coupling strength. This approach revealed that N(coh) of JC-1 J-aggregates ranges from 3 to 6.