Лако-красочные материалы — производство

Like many other pigment classes, DPP pigments fluoresce in solution. The Stokes shifts are in the range of 10-15 nm and the fluorescence quantum yields ca. 60% [16]. In the solid state, some DPPs show a minor fluorescence. Through N substi­tution, both the solubility and the Stokes shift can be increased.

Some specific N-substituted DPP also show a strong solid-state fluorescence. One interesting case has been described by Langhals [17], where the DPP 23 can

crystallize in two different crystal modifications, one strongly fluorescing and the other showing only a very weak fluorescence. The two modifications showing dif­ferent optical properties can be interconverted through a heating/crystallization process thus being principally interesting for information storage applications [18]. Another use as a light guide concentrator has been described [19].

As an alternative to N-alkylation or-arylation the formation of complexes, e. g., with Au, can also lead to highly soluble and strongly fluorescing DPP derivatives [20].

Further photophysical studies on fluorescing DPPs have been conducted by Johansson [21] including spectroscopic studies of a DPP in a lyotropic nematic liq­uid crystal and a comparison of the molecular symmetry of the ground state ver­sus the first excited state.

Table 11.2 Absorptions and emissions of DPP [9, 17].

11.3.3