Photochemical Transformations of Some 4′-Amino-2-Styrylpyridines and Their Salts

Abstract

'The photochelllical behavior of 4'-amino-, 4'-dimethylarnino-, 4'-diethylamino-, and 4'-di-n-propylamino-substit~~ted trans-2-styrylpyridine were studied. Ultraviolet irradiation of aqueous solutions of the bishydrochlorides and methiodide-hydrochlorides for moderate periods of time produced mixtures of the corresponding cis and trans isomers. Long irradiation times produced the corresponding dimers in all cases except that of trans-4'-di-n-propylamino-2-styrylpyridine. The cis isomers of the free bases and methiodides were isolated from the cis-trans mixtures. The trans-methiodides are not photochemically labile. The spectra of each pair of isomers were determined in water and in 50% methanol-water, with the exception of the 4'-di-n-propylamino derivative, which is not sufficiently water soluble. In addition, the spectra of the corresponding methiodides, hydrochlorides, bishydrochlorides, and methiodide-hydrochlorides were determined. T h e basic strengths of the nitrogens in the cis-trans isomer pairs of the free bases and methiodides have been determined spectroscopically in water and in 50% methanol-water.

Synthesis of Styrylbenzazole Photoswitches and Evaluation of their Photochemical Properties

“…These results underline how methylation at nitrogen converts these switches from purely photochemical P‐type to thermally reversible T‐type photoswitches. These results are in accordance with the observation that replacing a para ‐methoxy substituent with a para ‐dimethylamino substituent in a trans ‐2‐styrylpyridine methiodide dye, which is a structurally similar compound, even inhibits the E ‐ Z isomerization as a result of the increased single‐bond character of the central alkene bond [47] . For 5 a and 5 b , PSS ratios and quantum yields were determined at lower temperatures, at which the thermal back‐relaxation was sufficiently suppressed.…”

“…These results are in accordance with the observation that replacing a para-methoxy substituent with a paradimethylamino substituent in a trans-2-styrylpyridine methiodide dye, which is a structurally similar compound, even inhibits the E-Z isomerization as a result of the increased single-bond character of the central alkene bond. [47] For 5 a and 5 b, PSS ratios and quantum yields were determined at lower temperatures, at which the thermal back-relaxation was sufficiently suppressed. It was found that the quantum yields of both the forward and the back-reactions are very high.…”

Cyanines during the 1990s: A Review

“…William et al 184 studied the photochemical isomerization (trans-cis) of a series of styryl pyridinium dyes (84) by UV irradiation in aqueous and 50% (v/ v) MeOH-H 2 O solutions. They also observed dimer formation upon long irradiation of the dye solutions.…”

Novel environmentally benign procedures for the synthesis of styryl dyes

“…These coupling constants indicate the trans forms of the dyes in their ground states. It is known that each of the products can be transformed into the corresponding cis isomer by photolysis of their acidic solutions [19], but the cis styryl dye forms are not stable and readily undergo thermal isomerization to the trans form [19]. In addition, it has been reported that significant differences can be observed between the UVevis spectra of the cis and trans isomers [19].…”