Diazirine fluorescence

Diazirine fluorescence provides additional support for RIES.22 Excited di-alkyldiazirines (but not alkylhalodiazirines) fluoresce, and the fluorescence intensity increases with decreasing temperature, suggesting the existence of a barrier to nitrogen loss from the excited diazirine.22 For example, dimethyl-diazirine (35) and 35-df fluoresce upon pulsed laser excitation, with emission due to the excited diazirines. 

Photolysis of dimethyldiazirine produces a relatively small amount of car-bene. The major decay route is the formation of propene, without the intermediacy of dimethylcarbene. This mechanism was supported by isotope effect studies on the diazirine fluorescence and yield of carbene. [34]... 

The fluorescence is not quenched by pyridine (i.e., the excited diazirines do not react with pyridine), although the carbenes do react with pyridine to form ylides. Importandy, the fluorescence from diazirine 35-dt is 50% stronger than that of 35, and the pyridine-trappable yield of carbene 36-dt (from 35-df) is 50% greater than that of 36 from diazirine 35. These results parallel deuterium kinetic isotope effects on RIES.22... 

Thus, excited diazirine 35-d6 less efficiently undergoes 1,2-D migration with nitrogen loss compared to the analogous 1,2-H shift process in excited 35 accordingly, excited 35-dt more frequently decays by fluorescence than does... 

H shift more readily occurs with loss of nitrogen.22 Excited diazirines decay by fluorescence, carbene formation, or 1,2-H(D) migration coupled with N2 loss. C-D bonds are stronger than C-H bonds, so that deuteration retards the latter pathway and therefore RIES, leading to an increase in both fluorescence and carbene formation from 35-d6 22... 

In recent years, selective laser excitation and ultrasensitive fluorescence detection has been elegantly used to study isolated and single molecules, and Lu and Xie report that recent advances in near-field and far-field fluorescence microscopy now allow the imaging of single molecules and the recording of their fluorescence properties at room temperature. The exceptional photostability of 2-(2 -hydroxy-phenyl)perimidine has been discussed by Catalan et al. in relation to the fluorescence of the enol, and the reported value of 240 ps for the fluorescence lifetime of adamantyldiazirine represents the first such record for a diazirine (Buterbaugh et ai). Most phenanthrene derivatives do not usually exhibit... 

The first reported fluorescence lifetime of a diazirine has appeared and gives a lifetime for adamantyldiazirine of 240 ps at ambient temperature. A report has... 

Adamantyldiazirine is the first diazirine for which a fluorescence lifetime has been measured. Primary decay occurs with a lifetime of about 240 ps at ambient temperature, and increases at lower temperatures. The results support... 

Valence isomerization of diazoalkanes into diazirines and vice versa is possible by photolysis, although it is always accompanied by dediazoniation. The photolysis of diazirines was investigated intensively in recent years (e.g., by O Gara and Dailey, 1992, and by Modarelli and Platz, 1993 see also the book of Michl and Bonacic-Koutecky, 1990). An electronically excited state is obtained that can, in principle, decay by at least four competitive pathways (Scheme 5-16) a) fluorescence, b) intersystem crossing with the production of triplet carbene, c) formation of an excited diradical followed by internal conversion and production of singlet carbene, and d)... 

Gen atimi of Alkyl and Alicyclic Carbenes - A prompt, long-lived, red fluorescence has been observed in the photodissodation of jet-cooled diazirine, excited at the origin of the Sq- Si transition (323 nm). This emission is attributed to electronically excited singlet methylene, CH2 (b Bi), which is also highly vibrationally excited, and which appears to be formed directly from the S] state of diazirine. Products from the photolysis (350 nm, 25 °C) and pyrolysis (1(X)°C) of /rmajor product is the cyclobutene (12,44-64%), with smaller... 

The C5 position of dU has been used to attach a variety of labels or reporter groups, in particular fluorophores ° (see section 3.5). The pyrene-modified analogue (39) has been used to detect RNA bulge conformations in the HIV-TAR RNA sequence where the fluorescence is greatly enhanced,and as a donor for the red emitter nile red (40) when the two dyes are adjacent in duplex DNA the result is white light that is emitted upon excitation of (39). A zinc-porphyrin complex has been added to C5 of dU for use in electron transfer. Norbornene has been attached via an alkyne linker for post-synthetic modification with nitrile oxides in a copper-free Click reaction, " and various dienes have been attached for Diels-Alder tagging of DNA. The photoaffinity tag (41) has been incorporated into DNA adjacent to a damaged DNA base (8-oxo-dG or thymine dimer) such that when exposed to repair systems, the repair enzyme is trapped by the diazirine for mass spectroscopic characterisation. ... 

Disregarding inconsistencies in the natural fluorescence rate constants, it is important to note that aliphatic ketones (biacetyl and acetone) as well as several cis-azoalkanes show fluorescence in solution [81], This includes not only the examples of DBH-T [47,98] and DBO [56,103,138] (see Structnre 3.1), but also the smaller derivatives (see Structure 3.2) 2,3-diazabicyclo[2.1.1]hex-2-ene [139], diazirines, e.g., adamantyldiazirine [140], and even some sterically hindered azobenzenes [141], In contrast, DBH is not flnorescent with the exception of a report in siliceous zeohtes [66] it undergoes denitrogenation with unit quantum efficiency from the... 

Diazirines contain an N-N double boud constrained in a three-membered ring and have strong absorptions in both the infrared and ultraviolet/visible regions. The N=N stretching vibration of diazirines appears between 1560 and 1630 cm h In general, diazirines have an electronic absorption band between 310 and 350 nm (mi ), and a second absorption below 200 nm. Associated with the nJt transition is a weak fluorescence. " The fluorescence lifetime of adamantyldiazirine is on the order of 240 ps with a fluorescence quantum yield of about 0.0012 at ambient temperature. " (The lifetime increases with decreasing temperature.)... 

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