Photochemical nomenclature

Figure 4.1. Schematic representation of Born-Oppenheimer potential energy surfaces. Using the photochemical nomenclature, the ground-state surface of a closed-shell system, which is the lowest singlet surface, is labeled So, followed by S Sj, etc. in order of increasing energies. The triplet surfaces are similarly labeled T, Tj,...

The convenience gained by the use of the photochemical nomenclature is that ail isomers of the same formula have a common ground-state surface Sg. In the spectroscopist s convention, labels of crossing surfaces are kept and Sg of one isomer could lie above S, at the geometry of another isomer or even above itself, at the same geometry, provided two or more surfaces cross in an appropriate manner in several dimensions. ... 

Phosphorus heterocyclic compounds, 1, 493-538 five-membered ring systems, 1, 513-523 nomenclature, 1, 496 six-membered ring systems, 1, 497-513 Photoaromatization oxirenes from, 7, 125-126 Photobleaching chromenes in, 3, 880 Photochemical reactions heterocyclic compound synthesis from, 5, 159 reviews, 1, 56 heterocyclic compounds reviews, 1, 71, 72... 

The TR spectrum of the MLCT state comprising the predominant fraction of excited Ru(bpy)3+ species averaged over the timescale of our laser excitation pulse (7 ns) is shown in Figure 5 (lower trace). This predominant MLCT species has been variously denoted "triplet charge-transfer" ( CT) (45), "dTr " (43), or simply Ru(bpy)g+ (44). We adopt the latter nomenclature. It is the emissive and photochemically active state which has a lifetime of ca. 600 ns (room temperature, aqueous solution). 

In recent years luminescence nomenclature has become confusing within the literature and in practice. Luminescence involves both phosphorescence and fluorescence phenomena. While luminescence is the appropriate term when the specific photochemical mechanism is unknown, fluorescence is far more prevalent in practice. Moreover, the acronym LIE has historically inferred laser -induced fluorescence however, in recent years it has evolved to the more general term light -induced fluorescence due to the various light sources found within laboratory and real-time instruments. Within this chapter fluorescence and LIE are interchangeable terms. 

Nitrenium ions (or imidonium ions in the contemporaneous nomenclature) were described in a 1964 review of nitrene chemistry by Abramovitch and Davis. A later review by Lansbury in 1970 focused primarily on vinylidine nitrenium ions. Gassmann s ° 1970 review was particularly influential in that it described the application of detailed mechanistic methods to the question of the formation of nitrenium ions as discrete intermediates. McClelland" reviewed kinetic and lifetime properties of nitrenium ions, with a particular emphasis on those studied by laser flash photolysis (LFP). The role of singlet and triplet states in the reactions of nitrenium ions was reviewed in 1999. Photochemical routes to nitrenium ions were discussed in a 2000 review. Finally, a noteworthy review of arylnitrenium ion chemistry by Novak and Rajagopal " has recently appeared. 

The redefinition of some terms and the creation of new definitions will facilitate the expression of ideas that are currently of greatest interest. As far as the chemical aspect of the problem is concerned, especially with regard to organic photochemistry, the nomenclature used is largely that of ordinary reactions. For that reason, the development here will be concerned mainly with what Noyes, Porter, and Jolley (12) referred to as the "primary photochemical process." In addition, because of the growing importance of energy transfer in the study of photochemical systems and the almost complete lack of a coherent nomenclature, this aspect will be considered in the following treatment. 

III. SUGGESTED TERMS AND DEFINITIONS The difficulties in nomenclature described in the previous sections as well as others which arise in the photochemical "language" may be overcome by using the terms, definitions, and symbols given below. The basis of the suggested nomenclature is the clear distinction between (a) "step" and "process", (b) "primary" and... 

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