2-(1,1-Dicyanomethylene)rhodanine-Functionalized Oligothiophenes: A Structure-Property Investigation of / Photoisomerization Behavior.

A series of oligothiophenes singly and doubly functionalized with dicyanorhodanine (RCN) units have been investigated to understand their / photoisomerization behavior upon structural modulation. Monotopic RCN target molecules (-) were designed to observe the consequences of π-conjugation, solubilizing group substitution, and formylation of the thiophene units. In all cases, the isomer is obtained from synthesis as the thermodynamically stable isomer, whereas the isomer is achieved through selective irradiation (including red light, λ = 628 nm) as a / mixture in solution. For the quarterthiophene entries, photoisomerization is inhibited, with photoirradiation resulting only in degradation. The result comports with concentration-dependent studies, which show that increasing π-conjugation results in greater aggregation and muted / photoisomerization. Ditopic RCN targets (-), mimicking acceptor-donor-acceptor (A-D-A) oligomers relevant to OPV materials, also show evidence of photoisomerization in solution, with formation of / mixtures at the photostationary state (PSS). Complementary ground- and excited-state DFT calculations show excellent agreement with the experimental findings. This comprehensive structure-property analysis is expected to both guide and caution the functional materials community with respect to the usage of photoisomerizable RCN-oligothiophenes for optoelectronic applications.