Peryleneimide chromophores

Dendrimers with a polyphenyl core around a central biphenyl unit decorated at the rim with peryleneimide chromophores have been investigated both in bulk and at the single-molecule level in order to understand their time and space-resolved behavior [28]. The results obtained have shown that the conformational distribution plays an important role in the dynamics of the photophysical processes. Energy transfer in a series of shape-persistent polyphenylene dendrimers substituted with peryleneimide and terryleneimide chro-mophoric units (4-7) has been investigated in toluene solution [29]. 

Energy hopping among the peryleneimide chromophores, revealed by anisotropy decay times [30], occurs with a rate constant of 4.6x10 s E When three peryleneimide and one terryleneimide chromophores are attached to the dendrimer rim, energy transfer from the former to the latter units takes place with... 

Similarly, a number of terrylenediimide core dendrimers with semiflexible arms were investigated by our research group at the ensemble [17] and at the single molecule level [18]. Different generations of a polyphenyl dendrimer containing a terrylenediimide core with peryleneimide chromophores at... 

Figure 1.19a shows the partial amplitudes of p-C 1PX for this component as a function of the detection wavelength. First, considering only the mono-chromophoric compound p-ClPj (Fig. 1.19a [ ]) with a t2 of 6.3 ps, a change of sign of the partial amplitude can be observed. Taking into account the shape and the positive/negative behavior of this kinetic component, it is attributed to a vibrational relaxation in the electronically excited state of the peryleneimide chromophore. 

The fourth and the longest component (t4, a4) is in the range of a few nanoseconds and thus cannot be determined precisely in the time windows used here. Instead, the actual values were taken from measurements performed using a single-photon timing detection setup and is attributed to the intrinsic fluorescence lifetime of the peryleneimide chromophore equal to 4.2 ns. 

In first approximation, both features can be seen instantaneously after excitation and decay on a nanosecond time scale. Since the signal in the transient absorption spectrum above 600 nm is positive, it can predominantly be attributed to an excited state absorption (ESA) process. From previous studies, it is known that p-C lPj has a fluorescence quantum yield of almost unity and a fluorescence lifetime of 4.2 ns thus, the ESA found here can be attributed to S -S" absorption within the peryleneimide chromophore. 

Maus M, MitraS, LorM, Hofkens J, Weil T, Herrmann A, Mullen K, De Schryver FC (2001) Intramolecular energy hopping in polyphenylene dendrimers with an increasing number of peryleneimide chromophores. J Phys Chem A 105 3961... 

The steady state absorption and fluorescence spectra of both dendrimer generations 1 and 2 are depicted in Fig. 2. The former are merely superpositions of the absorption spectra of both chromophores involved. In the fluorescence, however, the peryleneimide part is almost completely quenched compared to the model compound. Instead, the fluorescence at wavelengths longer than 650 nm almost completely resembles the emission spectrum of the terrylene-diimide model compound 3. This feature is a strong indication that within these dendrimers the excitation energy is efficiently transferred from the peryleneimide to the terrylenediimide. 

This component is found in first and second generation dendrimers discussed here as well in the mono- and multichromophoric ones and is a combination of various processes resulting from the static and dynamic response of the environment of the chromophore [32]. Also, a fast relaxation of vibrationally excited levels (max. 2000 cm ) of the first singlet excited state in the peryleneimide cannot totally be excluded as a part of this component [32]. 

Another series of experiments was performed on p-ClP3, which contains three peryleneimides at the rim. Comparing the transient absorption spectra of this compound (see Fig. 1.26 top) to those of p-CIPi (Fig. 1.26, bottom), one can see that the general shape is identical. Since the same chromophore is involved, the attribution of the signals in p-C 1P3 can be the same as for p-CIPi. 

---