Five model compounds (Uu, Us, DPT, DMT, and MB) and two liquid crystalline poly(ester−urethane)s with inherent urethane and internal and external ester groups were prepared to monitor the hydrogen-bond (H-bond) interactions of urethane−urethane and urethane−ester (including internal and external esters). The model compounds were used to evaluate the extinction coefficient ratios between different free and bonded carbonyl absorption modes in the infrared spectra. The results show extinction coefficient ratios of εfree,u:εfree,ext:εbonded,ext:εbonded,u:εfree,int = 0.84:0.81:0.87:1.23:1.0. These ratios can then be used to approach mole fractions of different carbonyl groups in the oligomeric and polymeric poly(ester−urethane)s (as PEU-L and PEU-H, respectively) at different temperatures. For both PEU-L and PEU-H, their external ester carbonyl groups can compete efficiently with urethane carbonyl groups for H-bonds at elevated temperatures. Oligomeric PEU-L exhibited a major increase on the external ester carbonyl groups once heated to the mesomorphic state; in contrast, carbonyl variations on PEU-H proceeded in a continuous manner before the isotropization temperature. X-ray diffraction patterns suggest that PEUs form a smectic A layered structure. This result coupled with infrared study provided us the chain conformations of PEUs in their mesomorphic states.

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By appropriate chemical reaction, different substituents can be selectively attached to the four phenyl rings present in 2,3,4,5‐tetraphenylthiophene (TP) to prepare monomers, namely 2,5‐bis(4‐bromophenyl)‐3,4‐diphenylthiophene (BTP), 2,5‐bis(4‐bromophenyl)‐3,4‐bis[4‐(nonan‐1‐one)phenyl] thiophene (BTP‐N2) and 2,5‐bis(4‐bromophenyl)‐3,4‐bis[4‐(2‐heptyl‐4‐phenylquinoline)phenyl]thiophene (BTP‐Qu2). Three light‐emitting polymers, PTP, PTP‐N2 and PTP‐Qu2, with the common TP backbone were prepared by zero‐valent nickel‐catalyzed polymerization of BTP, BTP‐N2 and BTP‐Qu2 monomers, respectively. The substituent on the 3,4‐phenyl rings of the TP framework has a profound effect on the polymer properties. Without any 3,4‐substituent, the rigid PTP polymer has low solubility in organic solvents. With the flexible nonanoyl substituent, the corresponding polymer, PTP‐N2, has improved solubility but low quantum efficiency (ΦF) due to the carbonyl group which enhances intersystem crossing. With both flexible chain and bulky 4‐phenylquinoline (PQ) ring substituents, PTP‐Qu2 has good solubility and an enhanced ΦF since the introduction of both flexible chain and bulky PQ ring substituents prevents close chain packing. All three polymers exhibit similar emission spectra despite the distinct difference in the absorption pattern of PTP‐Qu2 compared with those of PTP and PTP‐N2. In the case of PTP‐Qu2, there is energy transfer from the PQ pendent ring to the TP backbone and results in emission similar to PTP and PTP‐N2. The TP backbone common in all the three polymers is responsible for the emission from the corresponding excited states. The electrochemical properties of PTP‐Qu2 were also investigated. Copyright © 2005 Society of Chemical Industry

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