Role of Planar Conformations in Aggregation Induced Spectral Shifts of Supermolecular Oligofluorenols in Solutions and Films: A Combined Experimental and MD/TD-DFT Study

Abstract

The supramolecular approach of fluorenol polymers brings about excellent self-assembly behavior to fabricate organogels and superstructured thin films through highly directional noncovalent interactions. To understand the aggregation effects on electronic structures, the packing structures and the UV/vis absorption spectra of oligofluorenols (PFOHn, n = 1/3-8), with and without OC8H17 side chains, were studied experimentally and theoretically in crystal, amorphous solids, and solutions, respectively. For the ground state in vacuum the steric repulsion between two adjacent fluorenol units renders the PFOH oligomers twisted in a helix conformation, while the molecular aggregation favors the appearance of planar π-conjugated structures. In comparison with the crystal packing, the content of planar conformation (with the torsion angle less than 20°) is increased in amorphous solids. The hydroxyl groups in oligofluorenols facilitate the formation of hydrogen bonding networks. The red shift in absorption spectra was observed in a systematic experimental study of unsubstituted and substituted oligofluorenols with the increasing concentration both in toluene and chloroform solutions. The subsitituted oligofluorenol R-PFOH1 with only one OC8H17 side chain exhibited a shoulder peak at 430-440 nm, which is different from PFOH1 without side chain and 3R-PFO1 with three OC8H17 side chain. Time-dependent density functional theory (TDDFT) calculations, which were carried out on conformation ensembles taken from a series of molecular dynamics (MD) simulations, revealed that the increase in the content of planar π-conjugated conformations is correlated to the red shift in the absorption spectra upon increasing the solution concentrations. The aggregation-induced red-shift in absorption spectra of oligofluorenols, as well as the blue-shift for oligothiophenes, was rationalized in a unified way from the increased (and reduced) content of planar conformations in molecular aggregates.

Triphenylamine and carbazole‐modified iridiumIII2‐phenylpyridine complexes: Synthesis, anticaner application and targeted research

“…To further understand how the ancillary ligands (TPA/Cz‐appended phenylpyridine) influence the anticancer activity, the optimal configurations, the frontier molecular orbitals and their electron cloud distribution were analyzed by density functional theory (DFT) method calculation at the B3LYP/6‐31G(d) (C, H, N, Cl)/lanl2dz (Ir) level with Gaussian 09 program, which are presented in Figure a. As shown, the HOMOs of complexes 1 and 3 are mainly localized on the central iridium atom, phenylpyridine ligand and the terminal TPA/Cz groups, while the LUMOs are mainly localized on iridium atom, phenylpyridine ligand and chlorine atom (the leaving group).…”

“…This conclusion confirms that target complexes enter cancer cells in a nonenergy‐dependent way . Simultaneously, laser confocal technology was also used to determine the subcellular localization in A549 cells due to the favorable target fluorescence property of Ir III complexes . A549 cells were incubated with complexes 1 and 3 for 1 hr at 37 °C, then co‐incubated with MTDR (Mito Tracker Deep Red, mitochondria fluorescent probe) and LTDR (Lyso Tracker Deep Red, lysosome fluorescent probe) for 20 min.…”

Unexpected solvent effects on the UV/Vis absorption spectra of o -cresol in toluene and benzene: in contrast with non-aromatic solvents

“…Owing to the thermal motions of solvent and solute molecules in solutions, it is easy to overcome the rotational barrier between trans and cis isomers in o -cresol, and subject to the dynamic conformation changes upon solvation in various solvents [ 51 ]. In some other systems [ 65 ], the conformation population can be changed by NCIs and the energetically high-lying isomer of the solute may exist in a condensed phase.

Figure 5.

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Diketopyrrolopyrrole‐based polymer fibrils formation by changing molecular conformation during film formation

“…The red‐shift indicated the longer effective conjugation length. The improvement of the conjugation length indicated the conformation of the conjugated polymer was changed …”