The Impact of Aggregation of Quaterthiophenes on the Excited State Dynamics

Abstract

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.

Understanding the Interaction between Inorganic and Organic Excitonic Components of an Inorganic‐Organic Nanohybrid Associate

“…However, sometimes red-shifted emission can also be seen from H-aggregates (especially for aggregates with slightly disordered arrangement of herringbone-like structures). [25,26] In case of J-aggregates, it is known that they form excitonic state due to delocalization of excitonic state between definite number of dye molecules. [6] These nanohybrid systems are fabricated such that colloidal QDs can act as donors of excitation energy and/or electrons to J-aggregates, which subsequently fluoresce and participates in different photophysical processes.…”

“…Due to this, there occurs bathochromic (red) or hypsochromic (blue) shift in the absorption and emission spectra of J‐ or H‐aggregate, respectively. However, sometimes red‐shifted emission can also be seen from H‐aggregates (especially for aggregates with slightly disordered arrangement of herringbone‐like structures) [25,26] . In case of J‐aggregates, it is known that they form excitonic state due to delocalization of excitonic state between definite number of dye molecules [6] .…”

Virtual Issue on Triplet Excitons

“…(3) In the achiral system, the spin orientations of triplet and singlet excitons are equal between spin-up (yellow cloud) and spin-down (green cloud) after TTET and TTA processes. (Panels a–f are reprinted from refs , , , , , and , respectively. Copyright American Chemical Society.…”

“…The suppression of the conformational mobility of quaterthiophene (QTH) in tetrahydrofuran solution with more than 70% water results in excitonically coupled H-aggregates. ISC was not observed [τ ISC = 330 ps (0% water), τ ISC = 2.3 ns (70% water)], and an unusual H-aggregate centered emission occurs from lower excitonic state of the QTH-aggregates when the water content goes to 100% (Figure e) . Incorporation of nonfullerene acceptors provided a sufficiently large energy difference and small electronic coupling between the CT and triplet excitonic states.…”

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

“…Reisner and co-workers have realized as many as 398 μmol of photocatalytic H 2 production per gram of C-dots per hour in the presence of a nickel co-catalyst . Significant efforts have been devoted to the synthesis and applications of C-dots; however, the study of the excited-state relaxation of C-dots using ultrafast spectroscopy and global and target analysis is less explored, which is essential for the development of efficient light-harvesting systems. − Wang et al have proposed an intrinsic dark state and a surface-related emissive state, which relaxes independently in the case of a carbon nanodot . On the contrary, previous works report the excitation transfer from the core to surface with various time scales ranging from 400 fs to 10 ps. , Yang and co-workers have demonstrated a detailed interplay between the core and surface in the excited state. , Wen et al have identified the time scale for various processes for the excited state of C-dots such as surface trapping (400 fs), optical phonon scattering (<5 ps), acoustic phonon scattering (50 ps), and excitonic recombination (1.5 ns) .…”