Solvent‐Sensitive Sign Inversion of Excimer Origin Circularly Polarized Luminescence in Bipyrenyl Peptides. Issue 26 (12th September 2017)

• Record Type: Journal Article
• Authors: Mimura, Yuki; Kitamura, Sayaka; Shizuma, Motohiro; Kitamatsu, Mizuki; Fujiki, Michiya; Imai, Yoshitane
• Is Part Of: ChemistrySelect. Volume 2:Issue 26(2017)
• Page Start: 7759
• Page End: 7764
• Publication Date: 2017-09-12
• Subjects: circular dichroism (CD) -- circularly polarized luminescence (CPL) -- peptides -- pyrenes -- solvent effects; Chemistry -- Periodicals; 540.5
• DOI: 10.1002/slct.201701315
• Languages: English
• ISSNs: 2365-6549

Abstract

Abstract: 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 (CHCl3, CH2 Cl2, MeOH, CH3 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 oppositely (+)/(–), respectively. On the other hand, in DD‐2/LL‐2, the excimer‐origin CPL signs were (–)/(+) in CH2 Cl2 (and CHCl3 ), respectively, and (+)/(–) in MeOH/DMF/NMP/DMAc, respectively. 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. Abstract : The excimer circularly polarized luminescence (CPL) of chiral peptides with two pendant pyrenyl groups is sensitive to solvents, with the sign of the CPL signal inverting on changing from a weakly polar solvent to a highly polar solvent. This effect is enhanced in peptides with longer, more flexible chains between the pyrenyl units.