Existence of Conformers Revealed by Spectral Analysis of Single Molecules of Perylene Orange in Thin Sol−Gel Films

Abstract

This paper reports on the spectral dynamics of perylene orange in thin sol-gel films. The studies are performed at the single molecule level to retrieve local information on such samples. The fluorescence spectrum of a molecule depends on the properties of the molecule itself and especially on its conformation in the ground state and in the state reached after excitation. Studies have been performed at room temperature and at a lower temperature, around 173 K. A large number of the recorded spectra reflect dual fluorescence. It is the rule at room temperature. However, at low temperature, single molecules either are relatively free to change conformation or are caught in a rigid environment. In the latter case, they present the spectrum of a rigid dye and we have identified the signature of several conformers of perylene orange in the ground state.

Improved performance of perylenediimide-based lasers

“…The main idea is that the groups attached to N atoms should avoid the interaction between neighbouring aromatic PDI cores. The strategies used in our case, that had lead to reach that end, and that might be somewhat generalized are: (i) use a rigid group with 35 an essentially perpendicular conformation with respect to the PDI core, as the phenyl groups of PDI-DXP and PDI-O; (ii) the positions at which additional substituents are added to the groups attached to the N atoms should be near the PDI core. This occurs in PDI-O and PDI-DXP, in which the isopropyl and methyl 40 groups respectively, are attached at C 2' and C 6' carbons (see Fig.…”

“…However, thanks to all these efforts, laser thresholds have been decreased so much that today it is possible to pump with cheap inorganic diode lasers 3 and even with light emitting diodes. 7 Therefore, these low-cost and compact optically-pumped lasers are by themselves useful for 35 applications. 1,2 Distributed feedback (DFB) resonators have been widely used to buid OSLs.…”

“…In particular, the cylindrical lens was replaced by a spherical one, so the beam over the sample (incident at  20º with respect to the normal to the film plane) was shaped into an elliptical spot (instead of a stripe) 35 with a minor axis of 1.1 mm. The emitted light was collected in a direction perpendicular to the film surface (instead of from the edge), by placing the fiber spectrometer at 1 cm from the sample.…”

“…However, for DXP perylene, whose chemical structure is very similar to that of PDI-O (the only difference is that the substituents attached to the C 2' and C 6' carbons in the phenyls -see Fig. 1 35 The lowest energy conformation for PDI-O is shown in Fig. 6(b).…”

“…6(a). In order to simplify the structure of the molecule in the scheme, the peripheral aliphatic chains have been replaced by methyl groups and only one of the two possible diastereomers (due to 35 rotation of the C-N bond) is shown. This conformation is confirmed by the 13 C NMR spectrum, which shows two carbonyl signals at 163.6 and 163.7 ppm, due to the asymmetric environment of the carbonyl groups.…”