1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 z Organic & Supramolecular Chemistry Solvent-Sensitive Sign Inversion of Excimer Origin Circularly Polarized Luminescence in Bipyrenyl Peptides Yuki Mimura, [a] Sayaka Kitamura, [a] Motohiro Shizuma, [b] Mizuki Kitamatsu,* [a] Michiya Fujiki,* [c] and Yoshitane Imai* [a] The photoexcited and ground state chiralities of enantiopure oligopeptides bearing two pyrenyl groups (DD-2/LL-2: four methylene spacer between two pyrenyl groups and DD-1/LL-1: no methylene spacer thereof) in eight common organic solvents (CHCl 3 , CH 2 Cl 2 , MeOH, CH 3 CN, DMF, NMP, DMAc, and acetone) were investigated by means of circularly polarized luminescence (CPL) and circular dichroism (CD) spectroscopies. It was found that chiroptical signs of pyrene-origin CPL and CD signals largely depend on the nature of solvents and are susceptible to the methylene spacer. Actually, the excimer- origin CPL signs at 450–510 nm of DD-1/LL-1 in DMF were (– )/(+), respectively, while those in other solvents were oppo- sitely (+)/(–), respectively. On the other hand, in DD-2/LL-2, the excimer-origin CPL signs were (–)/(+) in CH 2 Cl 2 (and CHCl 3 ), respectively, and (+)/(–) in MeOH/DMF/NMP/DMAc, respec- tively. The solvent dependent and the methylene spacer dependent CD sign inversion of DD-1/LL-1 and DD-2/LL-2 were also found. These results led to conclude that the solvent molecule and the methylene spacer collaboratively affect both the ground state chirality and the photoexcited chirality. Introduction Recently, chiral organic and organometallic luminophores that efficiently emit circularly polarized luminescence (CPL) in the near-ultraviolet, visible, and near-infrared regions have received a great amount of attention because of their unique optoelec- tronic and photonic applications. [1–4] In particular, the sign and magnitude of the CPL signal of chiral luminophores with non- restricted rotational freedom provide smart functions in the photoexcited state, which is susceptible to external stimuli. However, photoexcited chirality is difficult to control because the sign and absolute magnitude of CPL signals in the photoexcited state significantly differ from those of circular dichroism (CD) signals in the ground state, as the conforma- tions of molecules and complexes are significantly different in the ground and photoexcited states. [3] An enantiopair of luminophores with a stereogenic centre (s) in the ground state should provide mirror-image CPL signals with (+)- and (–)-signs in the photoexcited state. However, this approach has practical limitations because pairs of enantiopure luminophores may not always be available. Thus, a non- conventional approach for obtaining both (+)- and (–)-CPL signals from one enantiopure luminophore without the use of its enantiomer is a challenging issue. [4] Actually, such non- conventional sign inversion in CPL signals is possible with an appropriate solvent, [4a,k] host matrix, [4e] and stir direction at the sol-gel transition temperature, [4b] as well as by geometrical modification of the luminophore, [4c,d,g] heating and cooling, [4f,k] and aggregation and disaggregation. [4f,j,l] CPL spectra of several chiral oligo- and polypeptides with pyrenyl pendants have already been reported. [5] Recently, chiral oligopeptides with multiple pyrenes were found to emit intense excimer-origin CPL signals. [5i] Additionally, the CPL signs of these pyrenyl peptides were controlled by the intramolecular distance between two pyrene units. [5j] However, the possibility of solvent-controlled CPL sign inversion in chiral peptides has not yet been described. This work reports the first solvent-driven CPL sign inversion in bipyrenyl dipeptide enantiopairs with and without a four- methylene unit spacer to tune the intramolecular distance between the two pendant pyrenyl groups (Scheme 1): (i) HSp6-d-Ala(Pyr)-d-Ala(Pyr)-Sp6-NH 2 [DD-1] and its l-analogue (LL-1) and (ii) HSp6-d-Ala(Pyr)-NH-(CH 2 ) 4 -CO-d-Ala(Pyr)-Sp6- NH 2 [DD-2] and its l-analogue (LL-2). The sign of the excimer- origin CPL in each of these peptides with dd- and ll-stereo- centres was inverted on changing the solvent from chloroform (CHCl 3 ) to N,N-dimethylformamide (DMF). Results and Discussion Two types of bipyrenyl peptides, DD-1/LL-1 and DD-2/LL-2, were synthesized from Fmoc-Sp6-OH and Fmoc-d-Ala(Pyr)-OH [a] Y. Mimura, S. Kitamura, Dr. M. Kitamatsu, Dr. Y. Imai Department of Applied Chemistry Faculty of Science and Engineering Kindai University 3-4-1 Kowakae, Higashi-Osaka, Osaka 577-8502 (Japan) E-mail: kitamatu@apch.kindai.ac.jp y-imai@apch.kindai.ac.jp [b] Dr. M. Shizuma Department of Biochemistry Osaka Municipal Technical Research Institute 1-6-50 Morinomiya, Joto-ku, Osaka 536-8553 (Japan) [c] Prof. Dr. M. Fujiki Graduate School of Materials Science Nara Institute of School and Technology Takayama, Ikoma, Nara 630-0192 (Japan) E-mail: fujikim@ms.naist.jp Supporting information for this article is available on the WWW under https://doi.org/10.1002/slct.201701315 Full Papers DOI: 10.1002/slct.201701315 7759 ChemistrySelect 2017, 2, 7759 – 7764 # 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim