Photofunctional organic nanostructures of merocyanine dye fabricated via co-ion-assisted ion association: Morphology transformation from nanospheres to nanofibrils

Abstract

Organic nanoparticles of anionic chromophore merocyanine 540 (MC540) are synthesized on the basis of an ion association strategy using bis-quaternary phosphonium countercation o-xylylenebis(triphenylphosphonium) (XTPP) in the presence/absence of tetraphenylborate (TPB) co-anion. In the absence of TPB under a fixed XTPP concentration, produced MC540 nanoparticles are rather unstable and tend to form agglomerates or precipitates. In the presence of TPB co-anion, in contrast, the MC540 nanoparticles with high-stability and high-dispersibility are obtained. Notably, at a high incorporation level of TPB (TPB/MC540 = 3), morphology transformation from nanospheres to nanofibrils is found. From a viewpoint of photofunctionality, incorporation of TPB in the MC540-based nanoparticles makes the non-fluorescent H-dimers reduced, yielding an enhancement in their fluorescence quantum yields. Hence the present co-ion-assisted ion association protocol for fabricating anion-based organic nanostructures will play a key role in controlling not only their optical properties but also their nano-morphology.