Supramolecule-Regulated Photophysics of Oligo(p-phenyleneethynylene)-Based Rod–Coil Block Copolymers: Effect of Molecular Architecture

Computational investigation on the geometry and electronic structures and absorption spectra of metal-porphyrin-oligo- phenyleneethynylenes-[60] fullerene triads

In this work, we focus our attention on the influence of 2nd-row transition metals on the structural geometries, electronic structures, and absorption characteristics of porphyrin linked with the C₆₀ fullerene with oligo-p-phenyleneethynylenes (MP-C₆₀-oligo-PPEs) compounds. The DFT/B3PW91-D3 and CAM-B3LYP-D3/6-31G (d) calculations revealed that various metals embedded within the porphyrin moiety give different bridge conformations and different HOMO-LUMO energy levels. We calculate the UV-Vis spectra and absorption parameters using the time-dependent ZINDO/S approach. Our findings indicate that all the compounds have enhanced absorptions in the visible light range, and their molecular orbital energies adopt the condition of sensitizers. However, all of the complexes except down spin states exhibit considerably charge spatial separation. The results suggest that the ZnP-C₆₀-oligo-PPEs triad can meet the necessary conditions of the sensitizer of dye-sensitized solar cells (DSSCs) in comparison with other counterparts and could be an optimum triad compound for potential application in photovoltaic devices.

Resonance-Enhanced Charge Delocalization in Carbazole-Oligoyne-Oxadiazole Conjugates

There are notably few literature reports of electron donor-acceptor oligoynes, even though they offer unique opportunities for studying charge transport through "all-carbon" molecular bridges. In this context, the current study focuses on a series of carbazole-(C≡C)_n-2,5-diphenyl-1,3,4-oxadiazoles (n = 1-4) as conjugated π-systems in general and explores their photophysical properties in particular. Contrary to the behavior of typical electron donor-acceptor systems, for these oligoynes, the rates of charge recombination after photoexcitation increase with increasing electron donor-acceptor distance. To elucidate this unusual performance, we conducted detailed photophysical and time-dependent density functional theory investigations. Significant delocalization of the molecular orbitals along the bridge indicates that the bridging states come into resonance with either the electron donor or acceptor, thereby accelerating the charge transfer. Moreover, the calculated bond lengths reveal a reduction in bond-length alternation upon photoexcitation, indicating significant cumulenic character of the bridge in the excited state. In short, strong vibronic coupling between the electron-donating N-arylcarbazoles and the electron-accepting 1,3,4-oxadiazoles accelerates the charge recombination as the oligoyne becomes longer.

Amphiphilic Semiconducting Oligomer for Near-Infrared Photoacoustic and Fluorescence Imaging

Semiconducting polymer nanoparticles (SPNs) have emerged as an alternative class of optical nanoagents for imaging applications. However, the general preparation method of SPNs is nanoprecipitation, which is likely to encounter the issue of nanoparticle dissociation. We herein report nondissociable near-infrared (NIR)-absorbing organic semiconducting nanoparticles for in vivo photoacoustic (PA) and fluorescence imaging. The nanoparticles are self-assembled from an amphiphilic semiconducting oligomer (ASO) that has a hydrophobic semiconducting oligomer backbone attached by hydrophilic poly(ethylene glycol) (PEG) side chains. The ASO has a higher structural stability and brighter PA signals compared to those of its counterpart nanoparticles synthesized by nanoprecipitation. The small size and the PEG-passivated surface of the ASO allow it to passively target to and efficiently accumulate in the tumor of living mice, permitting tumor imaging with high signal-to-background ratios. Our study provides new NIR-absorbing organic nanoparticles for PA and fluorescence imaging, which also have the potential to be used as a drug carrier for theranostics.