Laboratoire de Chimie et Biochimie Pharmacologiques et Toxicologiques (CNRS UMR-8601), Université Paris Descartes, 45 rue des Saints Pères, F-75270 Paris Cedex 06, France.
J Am Chem Soc. 2010 Nov 24;132(46):16700-13. doi: 10.1021/ja108668h. Epub 2010 Oct 28.
The multifaceted potentialities of expanded pyridiniums (EPs), based on one pyridinium core bearing a 4-pyridyl or 4-pyridylium as the N-pyridinio group, are established at both experimental and theoretical levels. Two classes of head-to-tail (htt) EPs were designed, and their first representative elements were synthesized and fully characterized. The branched (B) family is made up of 2,6-diphenyl-4-aryl-1,4'-bipyridin-1-ium (or 1,1'-diium) species, denoted 1B and 2B for monocationic EPs (with aryl = phenyl and biphenyl, respectively) and 1B(Me) and 2B(Me) for related quaternarized dicationic species. The series of fused (F) analogues comprises 9-aryl-benzo[c]benzo[1,2]quinolizino[3,4,5,6-ija][1,6]naphthyridin-15-ium species, denoted 1F and 2F, and their 2,15-diium derivatives referred to as 1F(Me) and 2F(Me). Electrochemistry (in MeCN vs SCE) reveals that branched EPs undergo a single reversible bielectronic reduction at ca. -0.92 V for 1B/2B and -0.59 V for 1B(Me)/2B(Me), whereas pericondensed species show two reversible monoelectronic reductions at ca. -0.83 and -1.59 V for 1F/2F and ca. -0.42 and -1.07 V for 1F(Me)/2F(Me). Regarding electronic absorption features, all htt-EP chromophores show absorptivity in the range of ca. 1-4 × 10(4) M(-1) cm(-1), with red-edge absorptions extending toward 450 and 500 nm (in MeCN) for 2B(Me) and 2F(Me), respectively. These lowest-energy pi-pi* transitions are ascribed to intramolecular charge transfer between the electron-releasing biphenyl group and the htt-bipyridinium electron-withdrawing subsystems. EPs display room-temperature photoemission quantum yields ranging from 10% to 50%, with the exception of 1B, and branched luminophores are characterized by larger Stokes shifts (8000-10 000 cm(-1)) than fused ones. Lastly, a method to predict the efficiency of photobiscyclization of branched EPs into fused ones, based on the analysis of computed difference maps in total electron density for singlet excited states, is proposed.
基于一个吡啶核心，带有 4-吡啶基或 4-吡啶鎓作为 N-吡啶基，扩展吡啶鎓 (EPs) 具有多方面的潜力，这在实验和理论水平上都得到了证实。设计了两类头对头 (htt) EPs，并合成并充分表征了它们的第一个代表性元素。分支 (B) 家族由 2,6-二苯基-4-芳基-1,4'-联吡啶-1-鎓 (或 1,1'-二鎓) 物种组成，分别表示为单阳离子 EP 的 1B 和 2B(芳基 = 苯基和联苯基)和相关季铵化的二阳离子物种的 1B(Me) 和 2B(Me)。稠合 (F) 类似物系列包括 9-芳基-苯并[c]苯并[1,2]喹啉并[3,4,5,6-ija][1,6]萘啶-15-鎓物种，分别表示为 1F 和 2F，以及它们的 2,15-二鎓衍生物，称为 1F(Me) 和 2F(Me)。电化学 (在 MeCN 与 SCE 之间) 表明，分支 EPs 在约 -0.92 V 下经历单个可逆双电子还原，对于 1B/2B 为 -0.59 V，对于 1B(Me)/2B(Me)，而稠合物种在约 -0.83 和 -1.59 V 下显示两个可逆单电子还原，对于 1F/2F 和约 -0.42 和 -1.07 V 对于 1F(Me)/2F(Me)。关于电子吸收特征，所有 htt-EP 发色团在约 1-4×10(4) M(-1)cm(-1)的范围内显示出吸光度，对于 2B(Me)和 2F(Me)，红色边缘吸收分别延伸至 450 和 500 nm(在 MeCN 中)。这些最低能量的 pi-pi*跃迁归因于供电子联苯基团和 htt-联吡啶吸电子子系统之间的分子内电荷转移。EPs 显示出室温下的光致电子发射量子产率范围为 10%至 50%，除 1B 外，分支发光体的斯托克斯位移(8000-10000 cm(-1))大于稠合发光体。最后，提出了一种基于单重态激发态总电子密度差分图分析来预测分支 EPs 光双环化成稠合的效率的方法。
