Line Strength Expression in the Hybrid Basis Within a representation based on the hybrid basis set, the line strengths can be represented as a straightforward generalization of Eq.

A multimode Holstein Hamiltonian is used to describe optical excitations in quaterthiophene pinwheel aggregates. The Hamiltonian includes the coupling of excitons originating from the 1A(g)-->1B(u) electronic transition to phonons originating from the five intramolecular vibrational modes known from oligothiophene solution absorption/emission spectroscopy. The resulting eigenstates with lowest energy are best described as hybrid polaron phonons. The polarons are formed by coupling excitons with the higher frequency (688, 1235, and 1551 cm(-1)) vibrational modes, while the (optical) phonons arise from the lower frequency (161 and 333 cm(-1)) modes. The polaron phonons are responsible for the fine structure defining the A(1) band in the low-energy region of the absorption spectrum, ranging from the band origin to approximately 1500 cm(-1) beyond. The calculated A(1) band of quaterthiophene aggregates agrees favorably with that observed from thin films.

Using a Frenkel-exciton model, the degree of circular polarization of the luminescence (g lum ) from one-dimensional, helical aggregates of chromophoric molecules is investigated theoretically. The coupling between the electronic excitation and a local, intramolecular vibrational mode is taken into account. Analytical expressions for the fluorescence band shape and g lum are presented for the case of strong and weak electronic coupling between the chromophoric units. Results are compared to those from numerical calculations obtained using the three particle approximation. g lum for the 0-0 vibronic band is found to be independent of the relative strength of electronic coupling between chromophores and excitation-vibration coupling. It depends solely on the number of coherently coupled molecules. In contrast, for the higher vibronic transitions ͉g lum ͉ decreases with decreasing strength of the electronic coupling. In the limit of strong electronic coupling, ͉g lum ͉ is almost constant throughout the series of vibronic transitions but for weak coupling ͉g lum ͉ becomes vanishingly small for all vibronic transitions except for the 0-0 transition. The results are interpreted in terms of dynamic localization of the excitation during the zero point vibrational motion in the excited state of the aggregate. It is concluded that circular polarization measurements provide an independent way to determine the coherence size and bandwidth of the lowest exciton state for chiral aggregates.

The salient features in the absorption and emission spectra of αT4 aggregates (see Figure) and films are fully accounted for using a model based on linear exciton–phonon coupling and structural defects. In particular, the Davydov splitting is calculated to be of the order of 1 eV, and the unusually small 0–0 emission intensity is attributed to the high sensitivity of the 0–0 intensity to basal plane structural defects.

In order to promote the degradation of PLA in seawater, a series of seawater-degradable polyester blends PVA/PLA were prepared by blending biodegradable polylactic acid (PLA) with water-soluble modified polyvinyl alcohol (PVA) in this paper. ADR 4370S was introduced to bring a certain degree of improvement in compatibility of PVA/PLA blends. The results of degradation test in natural seawater for 180 days show that the weight loss of PVA/PLA blends in seawater is much higher compared with that of pure PLA. PVA can be used as an effective hydrolysis accelerator for PLA matrix, helping to significantly reduce the molecular weight of PLA. The channels caused by dissolution/swelling of PVA facilitate the entry of water and microorganisms into the materials to contact with PLA, thereby promoting the degradation process of PLA matrix itself. Thus, both dissolution/swelling of PVA and degradation of PLA occur in PVA/PLA blends, and the degree of rapid dissolution of PVA in the early stage determines the degree of degradation of PLA.