Ultrafast Electron Transfer Dynamics of Organic Polymer Nanoparticles with Graphene Oxide

We prepared organic polymer poly-3-hexylthiophene (p3ht) nanoparticles (NPs) and graphene oxide (GO)/reduced graphene oxide (RGO) composites p3ht NPs-GO/RGO by using the reprecipitation method. We demonstrated that GO/RGO could improve the ordering and planarity of p3ht chains as well as the formation of p3ht NPs, and confirmed the effects of GO/RGO on the fluorescence and carrier transport dynamics of p3ht NPs by using femtosecond fluorescence upconversion and transient absorption (TA) techniques. Ultrafast electron transfer (∼1 ps) between GO/RGO and p3ht NPs quenched the fluorescence of p3ht NPs, indicating excellent properties of p3ht NPs-GO/RGO as the charge transfer complexes. Efficient electron transfer may promote the applications of p3ht NPs-GO/RGO composites in organic polymer solar cells and photocatalysis. Moreover, RGO had stronger interfacial interactions and more matched conduction band energy levels with p3ht NPs than GO did, which implied that p3ht NPs-RGO might have greater application values than p3ht NPs-GO.

Deciphering the Relaxation Mechanism of Red-Emitting Carbon Dots Using Ultrafast Spectroscopy and Global Target Analysis

Red-emitting carbon dots (C-dots) have tremendous potential for bioimaging and optoelectronic applications. Here, we investigated the structural modification of red-emitting C-dots due to boron doping and their ultrafast relaxation dynamics. It is evident from the X-ray photoelectron spectroscopy study that the relative percentage of pyrridinic nitrogen is increased at the expense of amino nitrogen and graphitic nitrogen in B-doped C-dots. Transient absorption spectroscopy and global target analysis reveal the formation of an additional excited-state level that takes away a significant amount of the excited-state population after boron doping. This new excited state slows the initial relaxation process toward the emissive state from 317 to 750 fs and increases the overall lifetime from 1.03 to 1.45 ns in B-doped C-dots.

The Impact of Aggregation of Quaterthiophenes on the Excited State Dynamics

Oligothiophenes and their aggregates play a dominant role in optoelectronic and light-harvesting applications. Here, we controlled the degree of aggregation of 2,2':5',2″:5'',2‴-quaterthiophene (QTH) to shed light on the impact of the aggregation on the excited state dynamics. QTH aggregation realized the control over the Intersystem Crossing (ISC) rates and, in turn, the formation of triplet excited states via the simple addition of water to QTH solutions in THF. From global target analysis, the time scale was 345.5 ps for ISC for QTHs in THF, but it was 2.33 ns in the case of QTH solutions featuring 70% water. Notably, the excitonic coupling between closely packed QTHs occurred predominantly in the aggregates formed in the presence of large water concentrations. Relaxation dynamics of the resulting QTH-aggregates differed substantially from QTH solutions at lower water content. For example, QTH-aggregates lacked any triplet excited states, and the unusual emission occurs from lower excitonic states from these predominantly H-aggregates.

Implications of relaxation dynamics of collapsed conjugated polymeric nanoparticles for light-harvesting applications

The mechanism of the formation of nanoparticles (collapsed state) from the extended state of polymers and their ultrafast excited state relaxation dynamics are illustrated.