Synthesis and fluorosolvatochromism of 3-arylnaphtho[1,2-b]quinolizinium derivatives

Abstract

SummaryCationic biaryl derivatives were synthesized by Suzuki–Miyaura coupling of 3-bromonaphtho[1,2-b]quinolizinium bromide with arylboronic acids. The resulting cationic biaryl derivatives exhibit pronounced fluorosolvatochromic properties. First photophysical studies in different solvents showed that the emission energy of the biaryl derivatives decreases with increasing solvent polarity. This red-shifted emission in polar solvents is explained by a charge shift (CS) in the excited state and subsequent solvent relaxation. Furthermore, the polarity of protic polar and aprotic polar solvents affects the emission energy to different extent, which indicates a major influence of hydrogen bonding on the stabilization of the ground and excited states.

Cationic Organophosphorus Chromophores: A Diamond in the Rough among Ionic Dyes

“…Such relaxation dynamics has been attributed to the hypothesized anion migration that occurs in donor‐acceptor contact ion pairs upon photoinduced ICT in the absence of solvent relaxation (Figure 18 C), and ultimately produces a lower energy emissive excited state. It should be mentioned, in support of the mechanism, that the anion migration in the excited ion pair has been also proposed for some N ‐heterocyclic (acridinium, naphthoquinolizinium) cationic dyes [6a, d, 75] …”

“…The electrostatic noncovalent interactions between the charged components are known to have a substantial effect on the photophysical properties of the ionic dyes [6d–f] . Thus, it has been shown that the intensity of the pyridinium‐π exciplex emission depends on the nature of the counterion, and is enhanced in the presence of PF 6 − but quenched with halides [6b] .…”

Synthesis of 9-arylalkynyl- and 9-aryl-substituted benzo[b]quinolizinium derivatives by Palladium-mediated cross-coupling reactions

“…The absorption spectra of 9-(arylethynyl)benzo[ b ]quinolizinium derivatives 2a , b , d show two low-energy maxima between 380 nm and 450 nm which resemble the ones of similar aryl-substituted benzo[ b ]quinolizinium [34] and naphthoquinolizinium [36] derivatives (Fig. 3, Table 2).…”

“…In contrast, the phenanthryl-substituted derivative 2d shows fluorosolvatochromism, specifically indicated by the strong blue shift in CHCl 3 . This effect is presumably caused by a charge shift (CS) or, more likely, by a charge transfer (CT) in the excited state from the electron-donating aryl unit to the excited quinolizinium (Scheme 3) [57], which has been proposed also to take place in structurally resembling excited biaryl-type acridinium, benzo[ b ]quinolizinium and naphtho[ b ]quinolizinium derivatives [36,58–64]. The CS/CT leads to an intermediate excited molecule with a charge neutral quinolizinyl radical and the radical cation of the phenanthryl unit (Scheme 3) that is well stabilized in polar solvents after solvent relaxation.…”

“…In this context, Palladium-mediated cross-coupling reactions provide a powerful tool [21–27]; specifically, as these C–C coupling reactions have been demonstrated to be very useful for the introduction of various substituents to quinolizinium [28–33], benzo[ b ]quinolizinium [34–35] and naphthoquinolizinium [36] derivatives.…”