G. E. Busch

Bio: G. E. Busch is an academic researcher from Bell Labs. The author has contributed to research in topics: Picosecond & Ultrashort pulse. The author has an hindex of 5, co-authored 9 publications receiving 412 citations.

Formation and Decay of Prelumirhodopsin at Room Temperatures

Abstract: We have excited detergent-solubilized bovine rhodopsin at room temperature with 530-nm light pulses from a mode locked laser, and have observed the appearance and decay of a transient species that absorbs more strongly at 560 nm than does ground-state rhodopsin. Our data show that the absorbing intermediate appears in a time that is at least as short as the experimental resolution (about 6 psec) and decays with a life time of about 30 nsec. The extremely fast risetime supports the hypothesis that prelumirhodopsin is the product of the primary photoprocess.

Energy Decay Characteristics of Benzophenone

Abstract: We have studied the energy‐resolved decay of benzophenone in the gas phase at various pressures. In the ``isolated‐molecule'' case benzophenone is shown to exhibit the characteristics of strong coupling between the S1 and T1 vibronic levels. A small contribution from weakly coupled vibrational levels may also be present and is discussed in the context of a weak coupling model.

Picosecond‐gated optical amplifier

Abstract: A picosecond‐gated optical amplifier (PGOA) characterized by high gains (≳102), large extinction ratios (∼105), and short aperture times (∼10 psec) is described. The active component of the system is a saturable absorbing dye which is irradiated by a high‐intensity ultrashort laser pulse. The technique is illustrated by simultaneously gating and amplifying a weak picosecond continuum pulse propagating through a scattering medium. Performance characteristics of the PGOA and ultrafast shutters are compared.

Multiphoton Absorbing Materials : Molecular Designs, Characterizations, and Applications

Abstract: 4. Survey of Novel Multiphoton Active Materials 1257 4.1. Multiphoton Absorbing Systems 1257 4.2. Organic Molecules 1257 4.3. Organic Liquids and Liquid Crystals 1259 4.4. Conjugated Polymers 1259 4.4.1. Polydiacetylenes 1261 4.4.2. Polyphenylenevinylenes (PPVs) 1261 4.4.3. Polythiophenes 1263 4.4.4. Other Conjugated Polymers 1265 4.4.5. Dendrimers 1265 4.4.6. Hyperbranched Polymers 1267 4.5. Fullerenes 1267 4.6. Coordination and Organometallic Compounds 1271 4.6.1. Metal Dithiolenes 1271 4.6.2. Pyridine-Based Multidentate Ligands 1272 4.6.3. Other Transition-Metal Complexes 1273 4.6.4. Lanthanide Complexes 1275 4.6.5. Ferrocene Derivatives 1275 4.6.6. Alkynylruthenium Complexes 1279 4.6.7. Platinum Acetylides 1279 4.7. Porphyrins and Metallophophyrins 1279 4.8. Nanoparticles 1281 4.9. Biomolecules and Derivatives 1282 5. Nonlinear Optical Characterizations of Multiphoton Active Materials 1282

Microbial and animal rhodopsins: structures, functions, and molecular mechanisms.

Abstract: Organisms of all domains of life use photoreceptor proteins to sense and respond to light. The light-sensitivity of photoreceptor proteins arises from bound chromophores such as retinal in retinylidene proteins, bilin in biliproteins, and flavin in flavoproteins. Rhodopsins found in Eukaryotes, Bacteria, and Archaea consist of opsin apoproteins and a covalently linked retinal which is employed to absorb photons for energy conversion or the initiation of intra- or intercellular signaling.1 Both functions are important for organisms to survive and to adapt to the environment. While lower organisms utilize the family of microbial rhodopsins for both purposes, animals solely use a different family of rhodopsins, a specialized subset of G-protein-coupled receptors (GPCRs).1,2 Animal rhodopsins, for example, are employed in visual and nonvisual phototransduction, in the maintenance of the circadian clock and as photoisomerases.3,4 While sharing practically no sequence similarity, microbial and animal rhodopsins, also termed type-I and type-II rhodopsins, respectively, share a common architecture of seven transmembrane α-helices (TM) with the N- and C-terminus facing out- and inside of the cell, respectively (Figure ​(Figure11).1,5 Retinal is attached by a Schiff base linkage to the e-amino group of a lysine side chain in the middle of TM7 (Figures ​(Figures11 and ​and2).2). The retinal Schiff base (RSB) is protonated (RSBH+) in most cases, and changes in protonation state are integral to the signaling or transport activity of rhodopsins. Figure 1 Topology of the retinal proteins. (A) These membrane proteins contain seven α-helices (typically denoted helix A to G in microbial opsins and TM1 to 7 in the animal opsins) spanning the lipid bilayer. The N-terminus faces the outside of the cell ...

Isomerization through conical intersections.

Abstract: The standard model for photoinduced cis-trans isomerization about carbon double bonds is framed in terms of two electronic states and a one-dimensional reaction coordinate. We review recent work that suggests that a minimal picture of the reaction mechanism requires the consideration of at least two molecular coordinates and three electronic states. In this chapter, we emphasize the role of conical intersections and charge transfer in the photoisomerization mechanism.

The first step in vision: femtosecond isomerization of rhodopsin.

Abstract: The kinetics of the primary event in vision have been resolved with the use of femtosecond optical measurement techniques. The 11-cis retinal prosthetic group of rhodopsin is excited with a 35-femtosecond pump pulse at 500 nanometers, and the transient changes in absorption are measured between 450 and 580 nanometers with a 10-femtosecond probe pulse. Within 200 femtoseconds, an increased absorption is observed between 540 and 580 nanometers, indicating the formation of photoproduct on this time scale. These measurements demonstrate that the first step in vision, the 11-cis----11-trans torsional isomerization of the rhodopsin chromophore, is essentially complete in only 200 femtoseconds.

Conical intersection dynamics of the primary photoisomerization event in vision

Abstract: The primary photochemical event in vision, isomerization of the 11-cis chromophore in rhodopsin to the all-trans form, is one of the fastest natural photochemical processes known, taking less than a millionth of a millionth of a second. The molecular details of reactions of such rapidity are a stiff challenge to experimenters, but Polli et al. now report the characterization of the reaction using ultrafast optical spectroscopy with sub-20-femtosecond time resolution and spectral coverage from the visible to the near infrared. The data confirm that rhodopsin's extreme reactivity results from a molecular funnel mechanism that involves a 'conical intersection' between the potential energy surfaces of the starting and product molecules. Chemical reactions are usually described in terms of the movement of nuclei between the potential energy surfaces of ground and excited electronic states. Crossings known as conical intersections permit efficient transitions between the surfaces. It is shown here that ultrafast optical spectroscopy, with sub-20-fs time resolution and spectral coverage from the visible to the near-infrared, can map the isomerization of rhodopsin with sufficient resolution to shown that a conical intersection is important in this crucial event in vision. Ever since the conversion of the 11-cis retinal chromophore to its all-trans form in rhodopsin was identified as the primary photochemical event in vision1, experimentalists and theoreticians have tried to unravel the molecular details of this process. The high quantum yield of 0.65 (ref. 2), the production of the primary ground-state rhodopsin photoproduct within a mere 200 fs (refs 3–7), and the storage of considerable energy in the first stable bathorhodopsin intermediate8 all suggest an unusually fast and efficient photoactivated one-way reaction9. Rhodopsin's unique reactivity is generally attributed to a conical intersection between the potential energy surfaces of the ground and excited electronic states10,11 enabling the efficient and ultrafast conversion of photon energy into chemical energy12,13,14,15,16. But obtaining direct experimental evidence for the involvement of a conical intersection is challenging: the energy gap between the electronic states of the reacting molecule changes significantly over an ultrashort timescale, which calls for observational methods that combine high temporal resolution with a broad spectral observation window. Here we show that ultrafast optical spectroscopy with sub-20-fs time resolution and spectral coverage from the visible to the near-infrared allows us to follow the dynamics leading to the conical intersection in rhodopsin isomerization. We track coherent wave-packet motion from the photoexcited Franck–Condon region to the photoproduct by monitoring the loss of reactant emission and the subsequent appearance of photoproduct absorption, and find excellent agreement between the experimental observations and molecular dynamics calculations that involve a true electronic state crossing. Taken together, these findings constitute the most compelling evidence to date for the existence and importance of conical intersections in visual photochemistry.