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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 (α-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.

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 α-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^IIIPc)^- 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 charge-separated 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 α-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 α-OTiPc-S at 298 K.

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.

Steady-state and time-resolved fluorescence behavior of 4-cyano-4‘-pentylbiphenyl (5CB) in polymer-dispersed liquid crystal (PDLC) films sandwiched between two quartz substrates was characterized by the surface-limited excitation (SLE) and through-film excitation (TFE) methods, which were used to discriminate the emissions from the interface layer with the substrate and from the interior domain. Although PDLC films showed both the monomer and excimer emissions of 5CB, SLE gave a substantially greater contribution of the former in the fluorescence than TFE. By contrast, a neat nematic film of 5CB showed exclusively the excimer emission independently of the excitation methods. Time-resolved analysis of the excimer emission from PDLC films revealed double-exponential decay profiles with shorter-lived (1.5−1.8 ns) and longer-lived (12−17 ns) components, in which the former is dominant for the excimer emission obtained by SLE, while the latter takes a major part for that obtained by TFE. By contrast, the excimer emission from a neat nematic film of 5CB showed a single-exponential decay with a ~17 ns lifetime independently of the excitation methods. The unique fluorescence behavior of the PDLC films has been discussed in terms of different molecular aggregation features of 5CB in the interface layer and in the interior domain.

A new methodology for the fabrication of covalently bound multilayers has been developed on the basis of a self-assembled monolayer (SAM) prepared from 5-(2-methyl-1,3,2-dioxaborinan-5-yl)pentyltrichlorosilane (1). The SAM was prepared by immersion of an aluminized silicon wafer into a toluene solution of 1; its thickness was determined by ellipsometry to be 1.5 ± 0.3 nm, a value very similar to the molecular size of 1. The fabrication of a two-layer film was successfully achieved by hydrolysis of the boronate protecting group of the SAM with water/ethanol to the diol-terminated group followed by treatment of the hydrolyzed monolayer with a toluene solution of 1; the thickness (2.9 ± 0.3 nm) was nearly twice that of the starting monolayer. Similar treatment of the two-layer film with water/ethanol effected the selective hydrolysis of the boronate end group without significant loss of the second-layer unit, and subsequent reactions of the hydrolyzed two-layer film with 1 or octadecyltrichlorosilane smoothly occurred to give the corresponding three-layer assembly with thickness of 4.2 ± 0.4 or 5.4 ± 0.5 nm each.