PHTHALONAPHTHALOCYANINES - NEW FAR-RED DYES FOR SPECTRAL HOLE-BURNING

Mixed phthalocyanines carrying one anthracene (Pc(3)An) or substituted naphthalene nucleus (Pc(3)NcR(2), R = H, OCH3, or SC12H25) are propos ed as low-temperature photochroms for spectral hole burning. Solubilit y of these compounds in polymers was greatly enhanced by introducing t he 2,4-dimethyl-3-pentoxy substituent to the remaining three benzopyrr olic fragments. The wavelengths and intensities of the Q transitions ( S-1 and S-2) were measured for two prototropic tautomers having differ ent position of the pair of inner protons. The average energy of the t wo lowest transitions is very similar in both tautomers, although the S-1-S-2 Splitting is much smaller in the less stable form. The relativ e equilibrium concentration of the tautomers at room temperature depen ds on the electron releasing properties of the substituents. This allo ws one to predict the positions of protons in each form. Absorption di chroism of stretched polyethylene films was used in order to establish the direction of the S-1 and S-2 transition dipole moments in the mol ecular framework. The tautomers can be completely converted into each other at 10 K by light with quantum yields of (1-2) x 10(-3) and (5-8) x 10(-3), respectively, depending on the direction of the process. Mo st probably the phototransformation occurs in the vibrationally relaxe d triplet state via the tunneling of a single proton which results in an intermediate state with cis-configuration of protons. The photochem ically accumulated less stable form decays at higher temperatures (T) as a result of a thermally activated tunneling process at characterist ic T of 115 and 153 K for protonated and deuterated Pc(3)Nc, respectiv ely. The strength of linear electron-photon coupling (EPC), which is c rucial from the point of view of spectral hole burning, is characteriz ed by Debye-Waller factors (DWFs) about 0.6-0.75, depending on the com pound and the polymer matrix. The T dependence of quasihomogeneous hol e width (T-qh) obeys a power law with coefficients 2.5 +/- 0.5 (betwee n 6 and 30-45 K). In different polymer hosts, the DWF increases and th e hole width decreases in the following order: polystyrene, poly(vinyl butyral) > polyethylene. The strength of EPC for the lowest transitio ns is similar in both tautomeric forms. A slight enhancement of the EP C strength in the series of dyes Pc(3)Nc(OCH3)(2) similar to Pc(3)Nc < Pc(3)Nc(SC12H25)(2) < Pc(3)An is correlated with the increase of elec tron-withdrawing power of substituents, plausibly, as a result of the increase of dipole moment change upon electronic excitation. Spectrosc opic properties, phototautomerization quantum yields, and the EPC stre ngth of mixed phthalocyanines were compared with those of chlorin and porphyrins.