Mukhopadhyay Arindam, Jindal Swati, Maka Vijay Kumar, Moorthy Jarugu Narasimha
Department of Chemistry, Indian Institute of Technology, Kanpur 208016, India.
School of Chemistry, Indian Institute of Science Education and Research, Thiruvananthapuram 695551, India.
ACS Omega. 2021 Aug 2;6(32):21113-21124. doi: 10.1021/acsomega.1c02948. eCollection 2021 Aug 17.
Investigation of photochromic and acidochromic behaviors of a set of pyridyl- and pyrimidylethynylated mono- and bis-benzopyrans reveals an intriguing influence of the -heteroaryl ring on spectrokinetic properties of the photogenerated -quinonoid colored reactive intermediates. While the absorption maxima of the pyridylethynylated bis-benzopyran and its photogenerated -quinonoid colored species undergo bathochromic shifts by ca. 40 and 22 nm, respectively, in the presence of an acid (e.g., trifluoroacetic acid (TFA)), the same remain unaffected for the analogous pyrimidylethynylated bis-benzopyran and its photogenerated -quinonoid colored species under similar conditions. Modification of the photochromic behavior of these benzopyrans and, hence, spectrokinetic properties of their photogenerated -quinonoid species in the presence of H is a consequence of relative proton affinities of -heteroaryl rings, i.e., pyridyl/pyrimidyl, and the resonance effects relayed through the ethynyl spacers in a push-pull π-delocalized-type skeleton; the mesomeric effects operate in a contrasting manner depending on the -heteroaryl ring in the absence and in the presence of an acid. These molecular systems offer a unique opportunity to modulate both photochromic and acidochromic properties of benzopyrans and their photogenerated colored -quinonoid intermediates by leveraging -heteroaromatic rings.
对一组吡啶基和嘧啶基乙炔化的单苯并吡喃和双苯并吡喃的光致变色和酸致变色行为的研究揭示了杂芳基环对光生醌型有色反应中间体的光谱动力学性质的有趣影响。虽然在酸（例如三氟乙酸（TFA））存在下，吡啶基乙炔化双苯并吡喃及其光生醌型有色物质的吸收最大值分别发生约40和22 nm的红移，但在类似条件下，类似的嘧啶基乙炔化双苯并吡喃及其光生醌型有色物质的吸收最大值不受影响。在H存在下，这些苯并吡喃的光致变色行为及其光生醌型物质的光谱动力学性质的改变是杂芳基环（即吡啶基/嘧啶基）的相对质子亲和力以及通过乙炔间隔基在推挽π离域型骨架中传递的共振效应的结果；在不存在和存在酸的情况下，中介效应根据杂芳基环以相反的方式起作用。这些分子体系提供了一个独特的机会，通过利用杂芳环来调节苯并吡喃及其光生有色醌型中间体的光致变色和酸致变色性质。
