title: Electric Dipole Transition Moments and Solvent-Dependent Interactions of Fluorescent Boron-Nitrogen Substituted Indole Derivatives.
abstract: Fluorescent analogues of the indole side chain of tryptophan can be useful spectroscopic probes of protein-protein and protein-DNA interactions. Here we present linear dichroism and solvent-dependent spectroscopic studies of two fluorescent analogues of indole, in which the organic C═C unit is substituted with the isosteric inorganic B-N unit. We studied the so-called "external" BN indole, which has C2v symmetry, and the "fused" BN indole with Cs symmetry. We performed a combination of absorption and fluorescence spectroscopy, ultraviolet linear dichroism (UV-LD) in stretched poly(ethylene) (PE) films, and quantum chemical calculations on both BN indole compounds. Our measurements allowed us to characterize the degree of alignment for both molecules in stretched PE films. We thus determined the orientations and magnitudes of the two lowest energy electric dipole transition moments (EDTMs) for external BN indole, and the two lowest energy EDTMs for fused BN indole within the 30 000-45 000 cm(-1) spectral range. We compared our experimental results to those of quantum chemical calculations using standard density functional theory (DFT). Our theoretical predictions for the low-energy EDTMs are in good agreement with our experimental data. The absorption and fluorescence spectra of the external and the fused BN indoles are sensitive to solvent polarity. Our results indicate that the fused BN indole experiences much greater solvation interactions with polar solvents than does the external BN indole.
authors.affiliation: †Department of Chemistry and Biochemistry, Oregon Center for Optics, and Institute of Molecular Biology, University of Oregon, Eugene, Oregon 97403, United States.
authors.forename: Mari
authors.initials: M
authors.lastname: Saif
authors.affiliation: ‡Department of Chemistry, University of Michigan at Ann Arbor, Ann Arbor, Michigan 48109, United States.
authors.forename: Julia R
authors.initials: JR
authors.lastname: Widom
authors.affiliation: §Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Suzhou, Jiangsu 215000, China.
authors.forename: Senmiao
authors.initials: S
authors.lastname: Xu
authors.affiliation: ∥Chemistry Department, Eastern Washington University, Cheney, Washington 99004, United States.
authors.forename: Eric R
authors.initials: ER
authors.lastname: Abbey
authors.affiliation: ⊥Merkert Chemistry Center, Boston College, Chestnut Hill, Massachusetts 02467, United States.
authors.forename: Shih-Yuan
authors.initials: SY
authors.lastname: Liu
authors.affiliation: †Department of Chemistry and Biochemistry, Oregon Center for Optics, and Institute of Molecular Biology, University of Oregon, Eugene, Oregon 97403, United States.
authors.forename: Andrew H
authors.initials: AH
authors.lastname: Marcus
mesh_terms: D001895:Boron / Q000737:chemistry*; D007211:Indoles / Q000737:chemistry*; D008956:Models, Chemical; D015394:Molecular Structure; D009584:Nitrogen / Q000737:chemistry*; D020959:Polyethylene / Q000737:chemistry; D011789:Quantum Theory; D012997:Solvents / Q000737:chemistry*; D013050:Spectrometry, Fluorescence
chemical_list: D007211:Indoles; D012997:Solvents; C030374:indole; D020959:Polyethylene; D009584:Nitrogen; D001895:Boron