The impact of systematic structural variation on the energetics of π-π stacking interactions and associated computed charge transfer integrals of crystalline diketopyrrolopyrroles

Systematic variation in the bimolecular rate constant, k(q), for the reaction of singlet oxygen and 1,4-dimethylnaphthalene has led to estimates of the Hildebrand solubility parameter, cohesive pressures and internal energies of vaporisation of some room temperature ionic liquids.

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The effects of 0,-induced enhanced intersystem crossing (EISC) have long been recognised by workers investigating O2(lAg) quantum yields, t$, . However, no previous study employing techniques allowing direct 02('Ag) luminescence observation has addressed itself to quantifying s u c h effects. Employing energy-transfer techniques and investigating 0, concentration dependence of GA, allowed u s to determine S, , t h e fraction of triplets quenched by O2 giving rise to 02('Ag), under conditions where 0, ElSC can and cannot operate. The values of S, were found to be 0.65, 0.78, 0.76, 0.74, 0.78, 0.98 and 0.31 for pyrene, perylene, PPDME, TPP, ZnTPP, phenazine and benzophenone, respectively. With t h e exception of phenazine and benzophenone all compounds exhibited significant ElSC effects. W e have also observed 02(lAg) generation directly by 0, quenching of t h e first excited singlet state of perylene and pyrene.

Sensitive optical detection of nitroaromatic vapours with diketopyrrolopyrrole thin films is reported for the first time and the impact of thin film crystal structure and morphology on fluorescence quenching behaviour demonstrated.