Solvatochromism and acidochromism of azobenzene-functionalized poly(vinyl amines)

Structures, solvatochromism, protonation and photoswitching of tetra-(ortho)substituted azobenzenes bearing 3,5-dimethoxy groups

“…Negative “ b ” coefficients were reported also for azobenzenes with para -R–NH– substituents. 12 The negative value of “ b ” means that the excitation energy decreases in more basic solvents because of stronger hydrogen bonding interactions of proton acceptor solvent molecules with NH 2 group in the excited state than in the ground state of the molecules. This is in line with reported strong acidification of the NH 2 group of substituted anilines in the excited state.…”

“…The solvatochromism of donor–acceptor (or push–pull) substituted azobenzenes, involving a combination of strong electron donor and electron acceptor substituents, was studied most thoroughly in terms of the linear solvation energy relationships. 11–16 In this approach the wave number of the absorption maximum max is correlated by multiple linear regression to a set of empirical solvent parameters reflecting different types of intermolecular solvent–solute interactions. The most widely used are three sets of such parameters: Kamlet–Taft parameters (solvent dipolarity/polarizability π*, acidity α, and basicity β), 17 Catalan parameters (solvent acidity SA, basicity SB, polarizability SP, dipolarity SdP), 18 and Laurence parameters (dispersion-induction DI, electrostatic ES, solvent hydrogen-bond acidity and basicity α 1 and β 1 ) 19 with the respective regression eqn (1)–(3). Ñ max = 0 max + s π* + a α + b β max = 0 max + s SP + d SdP + a SA + b SB max = 0 max + di DI + e ES + a α 1 + b β 1 …”

Probing Solvation Effects in Binary Solvent Mixtures with the Use of Solvatochromic Dyes

“…The solvatochromism of azobenzene-based compounds has been thoroughly investigated in the past and there is clear evidence of the solvent dependent nature of the n!π* and π ! π* azo transitions [38][39][40][41]. This comes as no surprise as the nitrogen atoms of the azo group can readily interact with solvent molecules (in case of compound 1) or the interior groups of CyDs (alpha-for 2a and beta-for 2b).…”

Multi‐stimuli‐responsive Polymers Based on Calix[4]arenes and Dibenzo‐18‐crown‐6‐ethers

“…Lowering the pH of the THF solutions of the polymers results in the appearance of an absorption maximum at 530 nm, which is increased upon further addition of acid. This may be attributed to protonation of one of the nitrogen atoms of the azo-bridge 127 . The photo-isomerization on these protonated species could not be induced despite long irradiation times.…”