Über Pyridinium‐N‐phenolat‐Betaine und ihre Verwendung zur Charakterisierung der Polarität von Lösungsmitteln, XVIII. Synthese und UV/Vis‐spektroskopische Eigenschaften eines negativ solvatochromen Pyridinium‐N‐thiophenolat‐Betainfarbstoffs

Abstract

Synthesis and UV/Vis spectroscopic properties of the negathe @(30) values of 1 and the G(30) values of 2 for both aprotic tively solvatochromic, relative to 1 homomorphic, thiobetaine and protic solvents, despite of the fact that sulfur is usually dye 2 are described. The new thiobetaine 2 exhibits an even known to act as worse hydrogen-bond acceptor than oxygen. larger negative solvatochromism and thermochromism than Possible reasons for this extraordinary behaviour of 2 are disthe standard betaine dye 1, which has been used to establish cussed. In contrast to 2, the sulfo-substituted betaine dye 4 an empirical scale of solvent polarity, the so-called ET (30) does not exhibit any solvatochromism. scale. Surprisingly, there exists a linear correlation between Beim Losungsmittelwechsel Diphenylether -+ Wasser wird die Iangstwellige, intramolekulare Charge-Transfer-(CT-)UV/Vis-Absorptionsbande des intramolekular ionoiden Pyridinium-N-phenolat-Farbstoffs 1 um 357 nm (von 810 nach 453 nm) hypsochrom verschoben, begleitet von einer entsprechenden, mit dem Auge verfolgbaren Farbanderung der Losungen von 1. Diese auoergewohnlich groBe, im sichtbaren Wellenlangenbereich liegende, negative Solvatochromie macht 1 zu einem idealen empirischen Indikator der Losungsmittelpolaritat 3,4), der vielfaltige Anwendungen in der Korrelationsanalyse losungsmittelabhangiger Prozesse (Reaktionen und Absorptionen) gefunden hat 3,5). Die als quantitative, empirische Parameter der Losungsmittelpolaritat eingefuhrten und nach Gleichung (1) berechneten molaren Anregungsenergien ET(30) (Transition Energies in kcal . mol-') von l6) sind fur uber 300 Losungsmittel 3,4) und zahlreiche binare Los~ngsmittelgemische~~~) bekannt. Ursache der drastischen negativen Solvatochromie von 1 ist die mit zunehmender Losungsmittelpolaritat (d. h. mit zunehmendem Solvatationsvermogen des Losungsmittels) auftretende energetische Stabilisierung des dipolaren Elektronengrundzustandes von 1 relativ zum weniger dipolaren CT-Anregungszustand (pG > pA) durch differenzierende Solvatation beider Zustande. AuDer den nichtspezifischen zwischenmolekularen Wechselwirkungskraften zwischen gelostem Farbstoff und Losungsmittel wird die Solvatochromie von 1 in H-Briicken-Donor-(HBD-)Losungsmitteln vor allem durch die spezifische H-Briicken-Wechselwirkung zwischen Phenolat-Sauerstoffatom und protischem Losungsmittel entsprechend Gleichung (2) (X = 0) verursacht. ET(30)/(kcal .mol-') = h .c. t. N A --28591 2.8591. 1 0 -3~l c m -' =-A~,~, +ROH [ / . k (

Solvatochromism in Pure Solvents: Effects of the Molecular Structure of the Probe

“…For example, the "dielectric" or "non-specific" solute-solvent interactions are the sum of dipole-dipole, solute polarizability-solvent dipole, solute dipole-solvent polarizability and polarizability-polarizability interactions. I), followed by reference number): 1 [20]; 2 to 4 (present work); 5 [21]; 6 [22]; 7 [23]; 8 [24]; 9 [25]; 10 [26]; 11 [27]; 12 [16b]; 13 to 16 [28]; 17 [29]; 18 [30]; 19 [31]; 20 [32] and 21 to 26 [33]. ") iv) -A corollary to (iii) is as follows: for a group of probes, each tested in a series of solvents, it should be possible, in principle, to correlate the multiple regression coefficients of Eq.…”

“…(14) has the general form of a linear free energy relationship, and can be favorably compared with the Bronsted equation which correlates log (catalytic rate constant) with pK, of the catalyst. Keicnarat and bschner explained the unexpected sensitivity of probe (9) to HBD-solvents as a result of two effects: the S -ion of (9) is relatively free of steric hindrance by the 0, 0'-phenyl groups, and the charge density on S-is high because of unfavorable (3 p -2p) orbital overlap between sulfur and carbon [25]. carboxylic acids, and pyridines, but not when results of different classes of catalysts are plotted together [39].…”

Two‐Photon Solvatochromism II: Experimental and Theoretical Study of Solvent Effects on the Two‐Photon Absorption Spectrum of Reichardt’s Dye

“…[1,9,[14][15][16][17]35] Larger stabilization of the ground state, relative to the excited one, leads to negative solvatochromism. [15][16][17][36][37][38][39][40][41] In its ground electronic state, RD has a charge-separated, zwitterionic structure, which results in a dipole moment of about 15 D. [17] The vertical transition to the first excited state causes a significant decrease in the molecule polarity and the excited-state dipole moment is equal to 6 D. [17] Moreover, the conformation of RD depends on the environment, [42] strongly influencing nonlinear optical (NLO) properties, such as the first hyperpolarizability (b). [1,9,[14][15][16][17]35] 2,6-Diphenyl-4-(2,4,6-triphenyl-1-pyridinio)phenolate, commonly referred to as Reichardt's dye (RD) or B30, is a molecule that exhibits a strong negative solvatochromism, with the largest known solvatochromic shift.…”

“…[1,[15][16][17]35] The hypsochromic shift of its charge-transfer (CT) absorption band is from a maximum wavelength (l max ) of 810 nm in diphenyl ether to l max = 453 nm in water; this corresponds to a solvent-induced band shift of Dl max = À357 nm (Dn = 9730 cm À1 ). [15][16][17][36][37][38][39][40][41] In its ground electronic state, RD has a charge-separated, zwitterionic structure, which results in a dipole moment of about 15 D. [17] The vertical transition to the first excited state causes a significant decrease in the molecule polarity and the excited-state dipole moment is equal to 6 D. [17] Moreover, the conformation of RD depends on the environment, [42] strongly influencing nonlinear optical (NLO) properties, such as the first hyperpolarizability (b). [42] Twisted chromophores were studied with an eye towards new paradigms for molecular hyperpolarizabilities and electrooptics.…”

Ein Pyridinium‐Barbiturat‐Betainfarbstoff mit ausgeprägter negativer Solvatochromie: ein neuer Ansatz zur molekularen Erkennung

“…Dadurch weist das Barbiturat 3 eine höhere Empfindlichkeit gegenüber ¾nderungen der Lösungsmittelpolarität auf als bekannte, strukturähnliche Betainfarbstoffe (siehe Hintergrundinformationen). [10,11] Die individuellen Wechselwirkungen des Chromophors 3 mit der Solvensumgebung wurden mittels Lineare-Solvatations-Energie(LSE)-Beziehungen unter Verwendung der empirischen Lösungsmittelparameter nach Kamlet und Taft sowie Catalµn untersucht. [12,13] Die Solvatochromie von 3 wird demnach vorrangig von der H-Brückendonorfähigkeit und der Dipolarität des Lösungsmittels bestimmt, welche jeweils eine hypsochrome Verschiebung vonñ n max bewirken.…”