On the formation of non-emissive and emissive aggregates of regioregular poly(3-octylthiophene) in different local environments

• Aggregation behavior of regioregular poly(3-octylthiophene) (rr-P3OT) is investigated.
• Different types of aggregates form in solvent–nonsolvent systems.
• Loose packing of rr-P3OT chains results in non-emissive aggregates.
• Dense packing of rr-P3OT chains results in emissive aggregates.
• Photophysical properties of the aggregates depend on type of the solvents.

This contribution investigates the aggregation behaviors of regioregular poly(3-octylthiophene) (rr-P3OT) in solvent–nonsolvent systems. The photophysical properties of aggregates in different states are studied by utilizing UV/vis absorption, photoluminescent emission (PL) and photoluminescent excitation (PLE) spectroscopy. The rr-P3OT chains are dispersed in different solvents, including chlorobenzene (CRB) and pyridine (PRD). At this condition, the polymer chains are isolated in CRB or associated in PRD, depending on local polymer–solvent interactions. The polymer chains are forced to densely pack by adding a nonsolvent, ethanol. Ratio of the nonsolvent is systematically increased up to 99% (v/v). The aggregation of rr-P3OT chains results in the growth of distinct redshift peaks in absorption spectra. The measurements of site selective PL and PLE spectra detect the existence of two types of aggregates, non-emissive and emissive species. The formation of these two aggregates depends on local packing of rr-P3OT segments. An early stage of the interchain association results in the non-emissive species. When the chain segments are forced to densely pack within the aggregates, emissive species forms. The change of initial solvents also affects the photophysical properties of aggregates. The aggregates formed in the CRB and PRD systems exhibit rather different absorption patterns.

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