Odd–Even Effect of Thiophene Chain Lengths on Excited State Properties in Oligo(thienyl ethynylene)-Cored Chromophores

Abstract

In a self-assembly material system, odd–even effects are manifested from long-range periodic packing motifs. However, in an amorphous material system, due to long-range disorder, such phenomena are less prone to appear. Here, we report the discovery of a remarkable odd–even effect on the excited state properties of a series of conjugated thienyl ethynylene (TE) oligomers with truxene as end-capping units, Tr­(TE) n Tr (n = 2–6), in solution. Using steady-state and time-resolved spectral measurements, we found the fluorescence quantum yield and excited state dynamics, both showing odd–even alternation with increasing thiophene–ethynylene chain lengths in apolar cyclohexane (CHX). It is found that the symmetry properties with different torsional modes dominate the excited state processes. In polar tetrahydrofuran (THF), solvation lowers the twisting barriers, leading to symmetry breaking without special odd–even alternation over structures. The results presented here will be helpful for understanding odd–even effects of conjugated polymers and designing novel photoelectric materials.

Efficient photocatalytic hydrogen evolution with ligand engineered all-inorganic InP and InP/ZnS colloidal quantum dots

“…Time-resolved spectroscopy was then performed to obtain direct insight into the photophysical behavior of charge carriers. Femtosecond transient absorption (fs-TA) experiments were firstly conducted using a home-built femtosecond broadband pump-probe setup with time resolution around 100 fs as described previously in detail 47 . Concentrations of samples were adjusted to an absorbance of 0.3 OD at a pumping wavelength of 480 nm in 1 mm pathlength quartz cuvettes, and continuous stirring was performed during the test to alleviate photodegradation.…”

Effects of Fluorination on Exciton Binding Energy and Charge Transport of π-Conjugated Donor Polymers and the ITIC Molecular Acceptor: A Theoretical Study

“…This subtle decrease of E b can be related to the increase of the chain planarity as the molecular structure tends to assume a quinoid form. 22,88 The increase of the molecular planarity raises the electronic delocalization which contributes to the decrease in the exciton binding energy. 22 The results showed in Figure S2 suggest that the delayed time for exciton dissociation in small driven force blends might help to further decrease E b via relaxation of the molecular structure.…”

“…They show that (on average) the E b values decreased by ∼0.05 eV when calculated at the ES geometry, keeping the fluorinated materials with the lowest values. This subtle decrease of E b can be related to the increase of the chain planarity as the molecular structure tends to assume a quinoid form. , The increase of the molecular planarity raises the electronic delocalization which contributes to the decrease in the exciton binding energy …”

Intramolecular Energy Transfer in a Series of Star-Shaped Molecules with a Central Porphyrin Core and Four Oligocarbazole Arms

“…As shown in Figure a, the absorption spectrum of H 2 TPP is mainly in the visible region, including Q band with four distinct peaks in the range of 500–700 nm, corresponding to the electronic transition from the ground state to the first and second excited states (S 0 –S 1 and S 0 –S 2 transitions) and another strong absorption, the B band, at λ = 416 nm with a shoulder at ∼400 nm, derived from the S 0 –S 3 and S 0 –S 4 transitions. − For T­(OCA n )­Ps, the oligocarbazole arms have intense absorption in the UV region compared to H 2 TPP, which shows the main absorption peaks at 265, 293, and 343 nm, that are attributed to carbazole-centered π to π* transitions. ,− The peak at 343 nm arises from the S 0 –S 1 transition . Moreover, the absorption intensity of oligocarbazole increases nearly linearly at 293 nm as the length of the carbazole arms increases, indicating that the extended conjugate is NOT formed between the carbazole units (see Figure S1, Supporting Information). ,− The absorption spectra of the star-shaped molecules T­(OCA n )­Ps ( n = 2–6) with a central porphyrin core and oligocarbazole arms show a slight bathochromic shift (∼5 nm) in the B band and Q band compared to that of H 2 TPP, indicating that a weak electronic interaction exists between the two components . Also, there is no significant enlargement of the conjugation length with the increasing number of carbazole units in the T­(OCA n )­Ps, which is caused by the large torsion angle between the carbazole units, that will be discussed in the quantum chemical calculations section.…”