Metal-free synthesis, single crystal analysis and photophysical behavior of p-terphenyls

A simple and convenient metal-free approach for synthesizing p-terphenyls 7a–f is presented through a carbanion-induced ring transformation reaction involving 6-biphenyl-2H-pyran-2-ones 5 with pyruvic acetyl dimethyl aldehyde 6. Further the prepared dimethoxy p-terphenyls 7b-c,f were converted into diethoxy p-terphenyls 8a-c. The base-mediated ring transformation reactions proceeded smoothly under mild reaction conditions, resulting the formation of ring transformation products 7a-f and 8a-c in good to excellent yields. This synthetic approach allows the incorporation of both electron-withdrawing and electron-donating functionalities into p-terphenyl framework. Moreover, the structure of compound 7a was confirmed by its single crystal X-ray analysis. Additionally, the photophysical properties of synthesized p-terphenyls were analysed using UV-visible and fluorescence spectroscopy. Interestingly, the synthesized p-terphenyls 7a–f showed blue fluorescence in chloroform. The solvatochromic behaviour and concentration studies of compound 7d was also perforemd. Additionally, the thermal stability characteristics of compound 7d was also studied using TG and DTA analysis.