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Solvatochromic Azamethine Dyes for Probing the Polarity of Gold‐Cluster‐Functionalized Silica Particles
Author(s) -
Spange Stefan,
Kunzmann Dagmar,
Sens Rüdiger,
Roth Isabelle,
Seifert Andreas,
Thiel Werner R.
Publication year - 2003
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200304844
Subject(s) - solvatochromism , chemistry , cyclohexane , solvent , bathochromic shift , photochemistry , polarizability , absorption band , absorption (acoustics) , organic chemistry , molecule , materials science , fluorescence , physics , quantum mechanics , optics , composite material
Azamethine dyes of the merocyanine type [4‐( N , N ‐di‐ n ‐butylamino)‐2‐methylphenyl]{2,4‐di‐keto‐3‐[ N ′‐( n ‐hexyl)]‐5‐cyano‐6‐methyl‐3‐pyridinio}‐1‐azamethine ( 1 ) and [4‐( N , N ‐diethylamino)‐2‐( N ′‐ tert‐ butylcarboxy)‐amidophenyl]‐{2,4‐diketo‐3‐[ N ″‐( n ‐hexyl)]‐5‐cyano‐6‐methyl‐3‐pyridinio}‐1‐azamethine ( 2 ) have been used as surface‐polarity indicators for gold‐cluster‐functionalized silica particles. Their UV/Vis absorption maxima range from about λ =600 to 700 nm as a function of solvent polarity and are clearly separated from the surface plasmon UV/Vis absorption band of gold ( λ ≈520–540 nm). Solvatochromism of both dyes has been investigated in 26 solvents of different polarity. The positive solvatochromic band shifts of 1 and 2 can be well expressed in terms of the empirical Kamlet–Taft solvent polarity parameters α and π *. They are mainly sensitive to the dipolarity/polarizability ( π * term; 70–75 %) and HBD (hydrogen‐bond donating) acidity ( α term) of the solvent. Both dyes adsorb readily on functionalized silica samples from solutions in 1,2‐dichloroethane or cyclohexane. The surface polarities of gold‐cluster‐functionalized silica particles, with and without co‐adsorbed L ‐cysteine and poly(ethylenimine), have been investigated by using these solvatochromic dyes. The specific interaction of dye 2 with cysteine has been examined independently by quantum‐chemical calculations by using the AM1 and PM3 methods.