Conformational change, intrachain aggregation and photophysical properties of regioregular poly(3‐octylthiophene) in alkanes

Abstract

ABSTACT: This study explores the role of segmental solubility of regioregular poly(3-octylthiophene) (rr-P3OT) on chain organization and its photophysical properties. In good solvent chlorobenzene (CRB), rr-P3OT chain adopts an extended conformation, allowing long conjugation length of p-electrons. Cyclohexane is a good solvent for octyl side chain but a poor solvent for the thiophene backbone. The selective segmental interactions of rr-P3OT with this solvent induce conformational change of the polymer. Addition of cyclohexane into the CRB solution leads to chain coiling, which in turn causes significant decrease of the conjugation length. Absorption and photoluminescence spectra of the rr-P3OT in cyclohexane exhibit a blueshift of about 16 nm compared to those of the CRB solution. The change of chain conformation is also detectable by monitoring the variation of quantum yield upon increasing cyclohexane ratio. The quantum yield drops from 0.17 6 0.01 to 0.11 6 0.01 when the extended rr-P3OT chain transforms into coiled conformation. Hexane is a nonsolvent for rr-P3OT due to its relatively low solubility parameter. The addition of hexane into rr-P3OT solution in cyclohexane forces dense packing of thiophene rings within the coiled chain. An intrachain aggregation occurs in this system, leading to the appearance of three distinct redshift peaks in absorption spectra and the drastic drop of quantum yield. Correlation between the growth of redshift peaks and the decrease of quantum yield is clearly observed. FIGURE 8 AFM topography images of rr-P3OT on silicon wafer prepared by drop casting from 0.05 mg mL 21 solution in (a) mixed cyclohexane/hexane (60:40 v/v %) and (b) mixed cyclohexane/hexane (40:60 v/v %).

Structure difference of sorbitol derivatives influences the crystallization and performance of P3OT/PCBM organic photovoltaic solar cells

“…[36,38]. Obviously, with increasing the number of methyl groups, the d values of sorbitol derivatives slightly decrease, in the order as d DBS >d MDBS >d DMDBS , and subsequently the d difference with P3OT decreases, indicating the enhanced interaction between sorbitol derivative and P3OT with the increase of the methyl group on the phenyl rings.…”

Control over the photophysical properties of nanoparticles of regioregular poly(3-octylthiophene) using various poor solvents

“…An increase of the hexane ratio to 80% v/v results in additional redshift bands at about 558 and 605 nm, indicating the formation of aggregates [27,29,[32][33][34][40][41][42]. At this condition, some rr-P3OT segments stack on top of each other, causing intersegment delocalization of p electrons and the increase of conjugation length (i.e., decrease of HOMO-LUMO energy gap).…”

“…The PL and PLE spectra were carried out on PerkinElmer LS55 spectrometer. The quantum yield of rr-P3OT was measured as described in our previous report [40].…”

“…The increase of unfavorable interactions between polymer chains and poor solvent can drive inter-and intrachain aggregation. In our previous studies, we detect the formation of two types of rr-P3OT aggregates, nonemissive and emissive species, depending on strength of local segmental interactions within aggregates [40,41]. The loose packing of polymer chains in an initial state of aggregation results in non-emissive type.…”

“…The loose packing of polymer chains in an initial state of aggregation results in non-emissive type. The polymer chains are forced to densely pack upon increasing the ratio of poor solvent, causing the aggregates to emit light at relatively low energy region [40,41].…”