Figure 3d - f shows the correlation plot for the long dimer 2 along with the vibronic intensity ratio and FWHM as af unction of E 0 - 0 .W ed iscern the J - type coupling of the monomer units from the H - type coupling of the dimer by the redistribution of the oscillator strength to the vibronic transition for the most red - shifted emission : s tarting from the lowest E 0 - 0 and moving higher , the intensity of the vibronic sideband first decreases and then increases again , corresponding to as uppression of H - type coupling followed by ad ecrease in J - type coupling . T he same behavior is seen more clearly in the correlation plot of the peak FWHM in panel ( f ) . While the H - type coupling is only weakly visible for the long dimer , i ts hould become more pronounced for the short dimer as stated above . Q ualitatively , s ingle - molecule spectra of the short dimer 3 in panels Figure 3g - i also follow this trend , although the J - type character is less pronounced . TheH - type coupling is clearly visible as adistinctive increase of I 0 - 1 /I 0 - 0 at decreasing E 0 - 0 values . Asimilar correlation is also seen in the Huang - Rhys factors of the spectra , as discussed in Figure S16 . This representation of large sets of data offers an intuitive visualization of the non - trivial interplay between J - and H - type coupling in multichromophoric aggregates . I np articular , t he transition from J - to H - type behavior , indicated by the dashed blue lines , c onveys the impression that aq uantitative analysis of dipole - coupling strengths could be possible . W en ote that the overall PL intensity does not decrease significantly in H - type aggregates . Ther adiative rate decreases in such aggregates , b ut the PL quantum yield remains almost the same due to an egligible overall non - radiative rate in these molecules . [ 12 ] Ac omplete analysis of these characteristics would require careful considerations of the microscopic molecular dynamics involved , since the backbone can be quite flexible and the strongest Htype couplings may occur only within as mall region of the overall segment . [ 17 ] Then oise in the scatter plots of the peak width and the I 0 - 1 /I 0 - 0 ratio in Figure 3s hould also be noted . Thed ata for 2 Figure 3 . PL spectra of 2875 , 2743 , and 1857 single molecules of 1 , 2 and 3,s orted by the 0 - 0 peak - transition energy E 0 - 0 and normalized to I 0 - 0 .I n1,t he vibronic - intensity ratio I 0 - 1 /I 0 - 0 and spectral FWHM decreases with decreasing E 0 - 0 , ase xpected for J - aggregation . In 2 and 3,s pectral signatures of J - aggregation within the chromophores are identified in analogy to 1.Above acertain red - shift , t he spectral shape changes and H - aggregation dominates : t he spectra broadena nd the oscillator strengthshifts to the 0 - 1 transition . This threshold is indicated in blue . The vibronic - intensity ratio increases on either side of the set threshold . Green lines indicate averages over 50 points . and 3 show as omewhat larger scatter with the transition energy than for 1.The reason for this difference is simple : the additional degree of freedom - interchromophoric spacing , which determines the strength of H - type coupling in 2 and 3does not necessarily correlate fully with the effective chromophore length , that is , w ith the degree of J - type coupling . Very small variations in the interchromophoric spacing , as predicted by molecular - dynamics simulations , [ 17 ] have adrastic impact on the spectral width and vibronic coupling without necessarily affecting the transition energy , which is dominated by the degree of J - type coupling . These fluctuations show up as noise in the 2D plots , s ince , e ven in the regime where the spectra are dominated by J - coupling , H - type interactions can still occur , giving rise to spectral broadening and asuppression of I 0 - 0 .F inally , w es tress that this analysis approach is universal and can be applied to arange of different molecules .