Abstract:
The paper presents water and hydroxonium ion make orange color of $t$-azobenzene ($t$-AB) to be more pronounced and properties of the relevant electron excite band are in relationship with $\pi \rightarrow \pi^*$ transition of $t$-ABH$^+$ cation. This feature is evidencing, in contradiction with traditional memorizing, the $t$-AB visible electron excite band is, by its nature, $\pi \rightarrow \pi^*$ band but not $n \rightarrow \pi^*$ band. The feature reflects that AB molecule exists as two electronic tautomers, the non-polar tautomer prevails the polar which is forming by intra-molecular electron transfer from nitrogen $sp^2$-orbital to Rydberg $3S$-orbital of local $N=N$-chromophoric group. The transfer induces emergence colored cation of phenyl-aminyl type with $\pi \rightarrow \pi^*$ band in visible region.
Keywords:azobenzene, color, non-polar and polar electronic tautomers.
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