A Comparison of Structures and Optoelectronic Properties of Oxygen- and Sulfur-Containing Heterocycles:  Conjugated Nonylbisoxazole and Nonylbithiazole Oligomers

Abstract

The synthesis and characterization of 4,4′-dinonyl-2,2′-bisoxazole (NBO) and its oligomers are described. The optical, electronic, and structural properties of these oligomers, NBO, NBO 2 , and NBO 3 , are compared to their sulfur analogues (NBT, NBT 2 , and NBT 3 ). In the series (NBO) n and (NBT) n , there is a red shift in the λ max as "n" increases. This effect is observed in both the solid and solution states. The bithiazole oligomers have longer wavelength absorbances than those of the bisoxazole oligomers; however, the observed red shift is greater as "n" increases for the bisoxazole oligomers leading to a merging of the absorption maxima between the two systems. The larger red shift for the bisoxazole series is explained by the larger atomic orbital coefficients at the coupling sites of the bisoxazole oligomers versus those of the bithiazole derivatives. Both systems exhibit thermochromic behavior corresponding to a transition from an ordered to disordered state. Upon heating, the bisoxazole system shows a gradual conformational change indicated by continual blue shifts of the absorption maximum. Conversely, the less rigid bithiazole system exhibits an immediate order-disorder transition upon heating evidenced by the appearance of an isosbestic point in the absorption spectrum. The solid-state packing of the n ) 2 and 3 oligomers is very similar; however, the solid-state structures of NBO and NBT are different as determined by single-crystal X-ray diffraction. NBO packs in a two-layered "ribbonlike" structure, whereas NBT forms molecular stacks. The reduction potentials of (NBO) n increase (become more positive) from -2.97 to -2.60 to -2.46 V for n ) 1, 2, and 3, respectively, and the number of reductions observed corresponds to the number of NBO units.

Structure and Segmental Motions in a Substituted Polythiophene: A Solid‐State NMR Study

“…However, it may also be postulated that chromic phenomena can partly (or even only) reflect temperature‐dependent interchain interactions that accompany the formation (or disruption) of small aggregates or microcrystallites. Recently, many studies have been devoted to the analysis of the relative contribution of chromophore aggregation and planarization on the optical properties of the various chromic conjugated polymers 7–18. Among these studies, a series of analyses on oligothiophene model compounds and polythiophenes have suggested that the chromic effects observed in these organic materials are mainly due to conformational changes 14–17.…”

Affinitychromic Polythiophenes: A Novel Bio-Photonic Tool for High-Throughput Screening and Diagnostics

“…In the inverse process (formation of planar assemblies), the chromic behavior is probably the result of assisted planarization in which interchain interactions stacking forces the polymer chains into a more rigid conformation. 46,54 However, it was also postulated that thermochromic changes may reflect some interchain interactions (excitons, p-p stacking) that accompany the formation of small aggregates (this is obvious in the solid state) or microcrystallites. 46 Planarization always leads to a red shift, but the direction of the shift caused by aggregation depends on the details of the molecular packing in the solid state.…”

“…46,54 However, it was also postulated that thermochromic changes may reflect some interchain interactions (excitons, p-p stacking) that accompany the formation of small aggregates (this is obvious in the solid state) or microcrystallites. 46 Planarization always leads to a red shift, but the direction of the shift caused by aggregation depends on the details of the molecular packing in the solid state. Further studies will be required to determine the relative contribution of chromophore aggregation and planarization on the optical properties of various chromic conjugated polymers.…”

“…In the inverse process (formation of planar assemblies), the chromic behavior is probably the result of assisted planarization in which interchain interactions stacking forces the polymer chains into a more rigid conformation. 46,54 Figure…”

Conjugated Organometallic Polymers Containing Vollhardt's Cyclobutadiene Complex: Aggregation and Morphologies

“…[1] Aggregates of conjugated polymers such as poly(paraphenylene-vinylene)s, [2] poly(paraphenylene-ethynylene)s (PPE), [3] or polythiophenes [4] have significantly different physical, optical, and electronic properties from those of single molecules of these polymers. Aggregation of conjugated polymers is (potentially) relevant to device technology [5a, b] and molecular electronics, [5b] but is likewise of fundamental interest.…”