skip to main content


Search for: All records

Creators/Authors contains: "Boulanger, Sean A."

Note: When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external site maintained by the publisher. Some full text articles may not yet be available without a charge during the embargo (administrative interval).
What is a DOI Number?

Some links on this page may take you to non-federal websites. Their policies may differ from this site.

  1. null (Ed.)
    We discovered a novel fluorophore by incorporating a dimethylamino group (–NMe2) into the conformationally locked green fluorescent protein (GFP) scaffold. It exhibited a marked solvent-polarity-dependent fluorogenic behavior and can potentially find broad applications as an environment-polarity sensor in vitro and in vivo. The ultrafast femtosecond transient absorption (fs-TA) spectroscopy in combination with quantum calculations revealed the presence of a twisted intramolecular charge transfer (TICT) state, which is formed by rotation of the –NMe2 group in the electronic excited state. In contrast to the bright fluorescent state (FS), the TICT state is dark and effectively quenches fluorescence upon formation. We employed a newly developed multivariable analysis approach to the FS lifetime in various solvents and showed that the FS → TICT reaction barrier is mainly modulated by H-bonding capability instead of viscosity of the solvent, accounting for the observed polarity dependence. These deep mechanistic insights are further corroborated by the dramatic loss of fluorogenicity for two similar GFP-derived chromophores in which the rotation of the –NMe2 group is inhibited by structural locking. 
    more » « less
  2. null (Ed.)
    Since green fluorescent protein (GFP) has revolutionized molecular and cellular biology for about three decades, there has been a keen interest in understanding, designing, and controlling the fluorescence properties of GFP chromophore ( i.e. , HBDI) derivatives from the protein matrix to solution. Amongst these cross-disciplinary efforts, the elucidation of excited-state dynamics of HBDI derivatives holds the key to correlating the light-induced processes and fluorescence quantum yield (FQY). Herein, we implement steady-state electronic spectroscopy, femtosecond transient absorption (fs-TA), femtosecond stimulated Raman spectroscopy (FSRS), and quantum calculations to study a series of mono- and dihalogenated HBDI derivatives (X = F, Cl, Br, 2F, 2Cl, and 2Br) in basic aqueous solution, gaining new insights into the photophysical reaction coordinates. In the excited state, the halogenated “floppy” chromophores exhibit an anti-heavy atom effect, reflected by strong correlations between FQY vs. Franck–Condon energy ( E FC ) or Stokes shift, and k nr vs. E FC , as well as a swift bifurcation into the I-ring (major) and P-ring (minor) twisting motions. In the ground state, both ring-twisting motions become more susceptible to sterics and exhibit spectral signatures from the halogen-dependent hot ground-state absorption band decay in TA data. We envision this type of systematic analysis of the halogenated HBDI derivatives to provide guiding principles for the site-specific modification of GFP chromophores, and expand design space for brighter and potentially photoswitchable organic chemical probes in aqueous solution with discernible spectral signatures throughout the photocycle. 
    more » « less
  3. null (Ed.)
  4. Abstract

    Strategic incorporation of ameta‐dimethylamino (–NMe2) group on the conformationally locked green fluorescent protein (GFP) model chromophore (m‐NMe2‐LpHBDI) has drastically altered molecular electronic properties, counterintuitively enhancing fluorescence of only the neutral and cationic chromophores in aqueous solution. A ~200‐fold decrease in fluorescence quantum yield ofm‐NMe2‐LpHBDI in alcohols (e.g., MeOH, EtOH and 2‐PrOH) supports this GFP‐derived compound as a fluorescence turn‐on water sensor, with large fluorescence intensity differences between H2O and ROH emissions in various H2O/ROH binary mixtures. A combination of steady‐state electronic spectroscopy, femtosecond transient absorption, ground‐state femtosecond stimulated Raman spectroscopy (FSRS) and quantum calculations elucidates an intermolecular hydrogen‐bonding chain between a solvent –OH group and the chromophore phenolic ring –NMe2and –OH functional groups, wherein fluorescence differences arise from an extended hydrogen‐bonding network beyond the first solvation shell, as opposed to fluorescence quenching via a dark twisted intramolecular charge‐transfer state. The absence of ameta‐NMe2group twisting coordinate upon electronic excitation was corroborated by experiments on control samples without themeta‐NMe2group or with bothmeta‐NMe2andpara‐OH groups locked in a six‐membered ring. These deep mechanistic insights stemming from GFP chromophore scaffold will enable rational design of organic, compact and environmentally friendly water sensors.

     
    more » « less