A Latent Reaction in a Model GFP Chromophore Revealed upon Confinement: Photohydroxylation of <i>ortho</i>-Halo Benzylidene-3-methyl­imidazolidiones via an Electrocylization Process

Excited state behavior of halogen substituted model GFP chromophores was investigated in an acetonitrile solution and in a confined environment provided by an octa acid capsule in water. Of the <i>ortho</i>, <i>meta</i>, and <i>para</i> halogen substituted GFP chromophores only the <i>ortho</i> compounds gave a new product resulting from an unprecedented photosubstitution of halogens by the hydroxyl group. This unusual reaction highlights the importance of confined spaces in bringing about some unattainable photoreactions

Facile Formation of Graphene P–N Junctions Using Self-Assembled Monolayers

Monolithic and patterned aminopropyltriethoxysilane (APTES) layers are used to create n-doped graphene, graphene p–n junctions, and FET devices containing p–n junctions in the device channel through transfer of CVD graphene onto APTES coated substrates. APTES doping is shown to not result in introduction of defects. <i>I</i>–<i>V</i> measurements of FET devices containing patterned APTES layers show it is possible to control the position of the two current minima (two Dirac points) in the ambipolar p–n junction

Optically Modulatable Blue Fluorescent Proteins

Blue fluorescent proteins (BFPs) offer visualization of protein location and behavior, but often suffer from high autofluorescent background and poor signal discrimination. Through dual-laser excitation of bright and photoinduced dark states, mutations to the residues surrounding the BFP chromophore enable long-wavelength optical modulation of BFP emission. Such dark state engineering enables violet-excited blue emission to be increased upon lower energy, green coillumination. Turning this green coillumination on and off at a specific frequency dynamically modulates collected blue fluorescence without generating additional background. Interpreted as transient photoconversion between neutral cis and anionic trans chromophoric forms, mutations tune photoisomerization and ground state tautomerizations to enable long-wavelength depopulation of the millisecond-lived, spectrally shifted dark states. Single mutations to the tyrosine-based blue fluorescent protein T203V/S205V exhibit enhanced modulation depth and varied frequency. Importantly, analogous single point mutations in the nonmodulatable BFP, mKalama1, creates a modulatable variant. Building modulatable BFPs offers opportunities for improved BFP signal discrimination vs background, greatly enhancing their utility

Conformationally Locked Chromophores as Models of Excited-State Proton Transfer in Fluorescent Proteins

Members of the green fluorescent protein (GFP) family form chromophores by modifications of three internal amino acid residues. Previously, many key characteristics of chromophores were studied using model compounds. However, no studies of intermolecular excited-state proton transfer (ESPT) with GFP-like synthetic chromophores have been performed because they either are nonfluorescent or lack an ionizable OH group. In this paper we report the synthesis and photochemical study of two highly fluorescent GFP chromophore analogues: <i>p</i>-HOBDI-BF2 and <i>p</i>-HOPyDI:Zn. Among known fluorescent compounds, <i>p</i>-HOBDI-BF₂ is the closest analogue of the native GFP chromophore. These irrreversibly (<i>p</i>-HOBDI-BF₂) and reversibly (<i>p</i>-HOPyDI:Zn) locked compounds are the first examples of fully planar GFP chromophores, in which photoisomerization-induced deactivation is suppressed and protolytic photodissociation is observed. The photophysical behavior of <i>p</i>-HOBDI-BF2 and <i>p</i>-HOPyDI:Zn (excited state p<i>K</i>_a’s, solvatochromism, kinetics, and thermodynamics of proton transfer) reveals their high photoacidity, which makes them good models of intermolecular ESPT in fluorescent proteins. Moreover, <i>p</i>-HOPyDI:Zn is a first example of “super” photoacidity in metal–organic complexes