Laser chromophores

The development of tunable, narrow-bandwidtli dye laser sources in tire early 1970s gave spectroscopists a new tool for selectively exciting small subsets of molecules witliin inhomogeneously broadened ensembles in tire solid state. The teclmique of fluorescence line-narrowing [1, 2 and 3] takes advantage of tire fact tliat relatively rigid chromophoric... 

Reaction with vatious nucleophilic reagents provides several types of dyes. Those with simple chromophores include the hernicyanine iodide [16384-23-9] (20) in which one of the terminal nitrogens is nonheterocyclic enamine triearbocyanine iodide [16384-24-0] (21) useful as a laser dye and the merocyanine [32634-47-2] (22). More complex polynuclear dyes from reagents with more than one reactive site include the trinuclear BAB (Basic-Acidic-Basic) dye [66037-42-1] (23) containing basic-acidic-basic heterocycles. Indolizinium quaternary salts (24), derived from reaction of diphenylcyclopropenone [886-38-4] and 4-picoline [108-89-4] provide trimethine dyes such as (25), which absorb near 950 nm in the infrared (23). 

Delaire et al. [124] have reported that laser photolysis of an acidic solution (pH 2.8) containing PMAvDPA (23) and MV2 + allows the formation of surprisingly long-lived MV + - and DPA cation radicals with a very high charge escape quantum yield. The content of the DPA chromophores in PMAvDPA is as low as less than 1/1000 in the molar ratio DPA/MAA. Figure 20 shows a decay profile of the transient absorption due to MV + monitored at 610 nm [124]. The absorption persists for several milliseconds. As depicted in Fig. 20, the decay obeys second-order kinetics, which yields kb = 3.5 x 10s M 1 s. From the initial optical density measured at 610 nm, the quantum yield for charge escape was estimated to be 0.72 at 0.2 M MV2 +. ... 

Fig. 8. Examples of some of the donor-acceptor substituted TEEs prepared for the exploration of structure-property relationships in the second- and third-order nonlinear optical effects of fully two-dimensionally-conjugated chromophores. For all compounds, the second hyperpolarizability y [10 esu], measured by third harmonic generation experiments in CHCI3 solution at a laser frequency of either A = 1.9 or 2.1 (second value if shown) pm is given in parentheses. n.o. not obtained...

As aforementioned, diblock copolymer films have a wide variety of nanosized microphase separation structures such as spheres, cylinders, and lamellae. As described in the above subsection, photofunctional chromophores were able to be doped site-selectively into the nanoscale microdomain structures of the diblock copolymer films, resulting in nanoscale surface morphological change of the doped films. The further modification of the nanostructures is useful for obtaining new functional materials. Hence, in order to create further surface morphological change of the nanoscale microdomain structures, dopant-induced laser ablation is applied to the site-selectively doped diblock polymer films. 

Correct experimental conditions are vital. In particular, it is essential to irradiate only the benzophenone chromophore, which can be achieved by employing an appropriate u.v. laser, for direct excitation of the azo compound produces a singlet diradical that collapses to bicyclopentane. Oxygen pressure (150 psi) and reaction time (60-70 h) must be carefully regulated to obtain optimum yields (ca. 20%) of 9. 

Alvaro, M., Atienzar, P., Bourdelande, J.L., and Garda, H. (2004) An organically modified single wall carbon nanotube containing a pyrene chromophore Fluorescence and diffuse reflectance laser flash photolysis study. Chem. Phys. Lett. 384, 119-123. 

In the 1988-1999 period, almost all absolute kinetic studies of carbenic reactions employed LFP with UV detection. Carbenes that contain a UV chromophore (e.g., PhCCl) are easily observed, and their decay kinetics during reaction can be readily followed by LFP.11 However, alkyl, alkylhalo, and alkylacyloxycarbenes are generally transparent in the most useful UV region. To follow their kinetics, Jackson et al. made use of the ylide method, 12 in which the laser-generated carbene (2) is competitively captured by (e.g.) pyridine, forming a chromophoric ylide (3, cf. Scheme 1). The observed pseudo first order rate constants (kobs) for the growth of ylide 3 at various concentrations of pyridine are monitored by UV spectroscopy, and obey Eq. 1. 

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