Polyquinones [poly(2-methylanthraquinone-l,4-diyl) ], poly(anthraquinone-1,4-diyl) [P(1,4-AQ)], etc.] having -conjugation systems along their main chains have been prepared by an organometallic dehalogenation polycondensation of the corresponding dichloroquinones. P(2Me-l,4-AQ) is soluble in various organic solvents and has a molecular weight of 190 000 as determined by a light scattering method. Casting from solutions of P(2Me-l,4-AQ) gives films with good optical and mechanical quality. Chemical reductions of P(2Me-l,4-AQ) in V-methyl-2-pyrrolidone (NMP) with N2H4 and Na2S2Ü4 lead to the formation of a dianion (Q2~) and dihydrogenated species (QH2) of the quinone unit (Q), respectively. On the other hand, chemical reduction of P(2Me-l,4-AQ) with a mixture of Na2S204 and NaOH in NMP is interpreted by a stepwise mechanism involving formation of an intermediate radicalanion species (Q-~). Cyclic voltammogram of the P(2Me-l,4-AQ) film exhibits two redox cycles with E\ and E%°values of-1.38 and -1.69 V vs Ag/Ag+ corresponding to quinone/radical anion (Q/Q*~) and radical anion/dianion (Q*~/Q2~) redox couples, respectively. Reduction of P(2Me-l,4-AQ) and P(1,4-AQ) with sodium naphthalenide gives semiconducting materials.
Different types of ordered solid films of oxotitanium(IV) phthalocyanine (OTiPc) were grown
in 50−500 nm thickness by vacuum deposition onto such conventional substrates as metal-
and ITO-coated glass and neat glass at a rate of ∼0.05 nm s-1. Under 10-3−10-4 Pa isotropic
films with short-range molecular organization and preferential molecular orientation were
grown on the substrates kept at ∼25 °C but ordered α (phase II) or β (phase I) crystal films
on the substrates heated at 150 °C. The deposition onto surface-oxidized Al, Ti, and Cu/glass, ITO/glass, and neat glass at ∼25 or 150 °C selectively gave ordered isotropic or α-crystal
films which have preferential molecular alignments with “standing” orientations of the
molecular plane with respect to the substrate surface. On the other hand, another type of
ordered isotropic or β-crystal films with preferential “lying” molecular orientations was formed
by the deposition onto Au, Ag, and unoxidized Cu on glass at ∼25 or 150 °C. In the case of
150 °C-heated Pt/glass, the α-crystal film with “standing” molecular orientations was grown
under 10-3−10-4 Pa, but another type of α-crystal film with “lying” orientations under 2.7
× 10-5 Pa. Scanning electron microscopic observations of the ordered crystalline films
indicated that single-crystal-like domains are grown from the bottom to the top of the film
and are densely packed to give monolithic morphologies with little grain boundary. Visible−near-IR absorption and fluorescence spectra of the ordered solid films were recorded, showing
unique dependences on the molecular alignments involving anisotropic behavior in the
polarized absorption spectra of the α-crystal films with different molecular alignments.
A photochemical study was performed by means of femtosecond time-resolved absorption spectroscopy on novel polymorphs of thin crystalline oxotitanium(IV) phthalocyanine (OTiPc) n (n ) 2-4), β-OTiPc-L (phase I) and R-OTiPc-S (phase II), where the letters "L" and "S" mean "lying" molecular orientation and "standing" molecular orientation, respectively. A rapid change of the well time-resolved absorption spectrum in a range of 420-620 nm revealed that a part of the intrinsic exciton of β-OTiPc-L with the absorption maximum around 550 nm was in a lifetime of 0.5 ps converted to a charge-separated pair on the excitation of the 400 and 800 nm laser. The absorption bands at 430, 510, and ∼860 nm were left for a lifetime of 3 ps. The formation of the cationic π-radical inferred to be 2 (OTiPc) n-1 + is responsible for the absorption bands at 510 nm and that of the anionic species of 2 (OTi III Pc)is responsible for the band at 430 nm instead of the characteristic bands of the anionic π-radical of metallophthlocyanine around 600 nm. While the chargeseparated pair disappeared in 10 ps, another transient absorption at 490 nm was survived on the excitation of the 400 nm laser, which is assigned to the triplet exciton formed via intersystem crossing from higher state(s) of the singlet exciton. The time-correlated single photon counting technique revealed that a novel fluorescence of R-OTiPc-S with a peak at 10 420 cm -1 decaying biexponentially with a short (48-64 ps) lifetime and a long (101-416 ps) lifetime is assigned to the trapped excitons. A 10-fold increase in the initial intensity of the fluorescence at 77 K compared with at 298 K indicates that the yield of long-lived and fluorescent exciton is smaller than 0.1 on the excitation of R-OTiPc-S at 298 K.
Surface modifications of gold-on-glass substrates with organic thin layers exerted remarkable effects on the molecular alignment in the ordered solid films of oxotitanium(IV) phthalocyanine (OTiPc) grown by conventional vapor deposition (VD). While VD onto a gold-on-glass substrate heated at 150 °C gave a highly ordered phase I (β-form) crystalline film with parallel molecular orientations, ordered phase II (R-form) crystalline films with an obliquely standing molecular arrangement were selectively grown on the surfaces of the substrate modified with 9-cycle Langmuir-Blodgett layers of OTiPc, a self-assembled monolayer of octadecanethiol, and a spin-coated thin film of polyimide. Moreover, VD of OTiPc onto a rubbed polyimide film gave an in-plane ordered phase II film in which obliquely standing OTiPc molecules are aligned with the molecular plane parallel to the rubbing direction. This film revealed high dichroic behavior in the p-polarized visible and IR absorption spectra. The substrate-surface effects are discussed in terms of initial formation of "director layers" by interactions of depositing molecules with the organic surfaces.
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