Triarylmethanes properties

Other cationic dyes of potential interest in PDT are the triarylmethanes, such as Victoria Blue BO (Figure 11) and cyanines such as V,V -bis(2-ethyl-1,3 dioxolane)kryptocyanine (EDKC) (Figure 12), the latter having the rather unique property of oxygen-independent phototoxicity [44], Unfortunately, this compound also suffers from instability in solution. 

Consequently, PAM with not substituted triarylmethane fragments in basic chain surpass PAM on basic not substituted diamines two times on itself stabilizing properties. 

Low-symmetry molecular species can appear as a result of restricted reorientation and the interplay between stere-ogenic units. A tris-triarylmethane system containing chlorine atoms in all aromatic positions (3) has only three protons, one in each of the arylmethane units. However, the NMR spectrum of this species in solution (Figure 2) displays 16 proton signals. The unequal intensities of the peaks point out that they belong to different conformations in slow exchange. Analysis of the rather complex stereochemical properties of this system confirms the existence of six diastereomeric forms, five of which have Cl symmetry and therefore three proton signals, and one has C3 symmetry and contributes only one additional proton. 

During the period up to 1963, hexaarylbiimidazoles were primarily studied for their physical, principally, photochromic properties. Work at the Organic Chemicals Department of the DuPont Company was primarily concerned with the color-forming interaction between HABls and triarylmethane leucodyes. The group working in this area had little familiarity with photopolymerization, but did periodically try to interest another company division, the Photo Products Department in examining various novel HABls as photoinitiators. 

---