1,3,5-hexatriene derivatives excited states

Similarly, l-anilinonaphthalene-8-sulfonic acid (ANS) only emits in a hydrophobic environment, being almost completely quenched in aqueous solution. ANS and some other dyes, including 6-(p-toluidinyl)naphthalene-2-sulfo-nate, pyrene, l,6-diphenyl-l,3,5-hexatriene, fluorescein, and rhodamine derivatives attached to long acyl chains or to fatty acids that localize in the cellular membranes were used as probes for hydrophobic sites in proteins, protein folding, imaging of membranes of the cell, and solvent polarity. Pyrene-labeled fatty acids were used to detect the fusion of two membranes. When present in a membrane at sufficiently high concentrations, pyrene excimers (excited-state dimers) are formed that emit at 470 nm. Upon fusion with other membranes, probe concentration decreases, and excimer fluorescence is replaced by monomer fluorescence at 400 nm. This process can be monitored by ratiometric detection of pyrene labels. 

It has been known for some time that hexatrienes can be formed by reaction of excited benzene molecules with solvent in a frozen glass (262-264). Some details of the mechanism of this process have been deduced by Simons and Smith (90). They propose that intermolecular vibronic interaction with solvent is a necessary but not sufficient requirement for production of hexatrienes in viscous media. The reaction is associated with radiationless decay of the triplet state rather than a bimole-cular reaction of triplet benzene with neighboring solvent molecules. Since radiationless decay constitutes intersystem crossing, the product of the reaction is also in the ground state. It is stressed by the authors that hexatrienes are not produced in fluid media or by nonphosphorescent benzene derivatives in which there is a rapid competing decay of the triplet state. 

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