Masamitsu Inoue

Photopumped laser oscillation and charge-injected luminescence from organic semiconductor single crystals of a thiophene/phenylene co-oligomer

We have demonstrated that single crystals of a thiophene/phenylene co-oligomer [α,ω-bis-biphenyl-4-yl-terthiophene (BP3T)] show interesting photonic aspects: (1) the self-waveguided amplified spontaneous light emissions with a comparable low threshold of 8μJ∕cm2 to other optimized organic solid-state laser systems, and (2) the laser oscillation based on the optical self-confinement effect in the crystals. We have also presented electroluminescence from the crystals based on bipolar injection and the crystals’ tolerance for intense current driving. These achievements strongly imply that BP3T crystals are a promising candidate for organic laser diodes.

Light Emission from Organic Single-Crystal Field-Effect Transistors

We have demonstrated electroluminescence from field-effect transistors (FETs) of an organic single crystal. We used top-contact-configuration FETs with Au and Al (or MgAg) as source and drain electrodes, respectively. The devices exhibited p-type unipolar behavior and light emission depending on gate voltages and metal species of the drain contact. Moreover, the light intensity increased in the saturation region of drain current.

Organic field-effect transistor of (thiophene/phenylene) co-oligomer single crystals with bottom-contact configuration

A novel and simple fabrication technique of organic field-effect transistors (FETs) of organic single crystals with bottom-contact configuration was proposed. The organic single crystal that was made by vapor phase growth was used as a FET semiconductor layer. The proposed fabrication process of the device is quite simple. That is, a single crystal is only placed on an electrode-prepared substrate. The devices exhibited good bottom-contact type FET characteristics, and the field-effect mobility reached 0.15 cm2V-1s-1 in the best device, which was higher than that of thin film transistors that were prepared by vacuum evaporation.

Alternating copolymers containing an aromatic chromophore in every monomer unit 1.: Fluorescence properties of poly(benzyl methacrylate-alt-styrene)

Alternating copolymer of benzyl methacrylate and styrene (a-BzSt) was synthesized and its fluorescence properties were compared with those for alternating copolymer of methyl methacrylate and styrene (a-MSt) and the corresponding random copolymers. Both a-BzSt and a-MSt exhibited a predominant monomer emission which decayed exponentially, indicating no excimer formation in these polymers. However, the styrene and methacrylate monomer units in a-BzSt were found not to have exactly the same chromophores because differences in the fluorescence intensity and lifetime were observed. The fluorescence quenching studies showed that there was no noticeable increase in the quenching efficiency for a-BzSt and a-MSt compared with that for the corresponding random copolymers. Therefore, energy migration contributes inefficiently to the quenching in these alternating copolymers. This may be due in part to an intrinsically low migration efficiency of phenyl chromophores.

Alternating copolymers containing an aromatic chromophore in every monomer unit 3. Intramolecular excimer formation and energy transfer in poly(1-naphthylmethyl methacrylate-alt-2-vinylnaphthalene)

Abstract Alternating and random copolymers of 1-naphthylmethyl methacrylates (1NpMMA) and/or 2-vinylnaphthalene (VNp) were synthesized, and their fluorescence properties compared in tetrahydrofuran (THF) or 1,4-dioxane. The alternating copolymer of 1NpMMA and styrene (a-1NpSt) was found to form an excimer as freely as the corresponding random copolymer, and poly(1NpMMA-alt-VNp) (a-1NpVNp) also showed an excimer emission, indicating that excimer formation between the naphthyl (Np) chromophores in the alternating methacrylate sequences cannot be inhibited. The observation of monomer emission for 1NpVNp-type copolymers suggests that energy transfer occurs favourably from the 1NpMMA units to the VNp ones at room temperature, and that the transfer in the opposite direction, i.e., the transfer from the VNp units to the 1NpMMA ones, is possible at higher temperatures. The fluorescence-quenching study, however, showed no enhancement of the quenching efficiency for a-1NpVNp at room temperature. The predominant one-way energy transfer might not facilitate the long-range energy migration along the polymer chain.

Alternating copolymers containing an aromatic chromophore in every monomer unit IV. Intramolecular triplet–triplet annihilation in copolymer of 9-phenanthrylmethyl methacrylate and 9-vinylphenanthrene in rigid solution

Abstract The total and delayed emission spectra of the alternating copolymer of 9-phenanthrylmethyl methacrylate (PhMMA) and 9-vinylphenanthrene (VPh) (a-PhVPh) in a rigid solution at 77 K were compared with those of poly(PhMMA-alt-styrene) (a-PhSt), poly(methyl methacrylate-alt-VPh) (a-MVPh), and the corresponding random copolymers. All the fluorescence, phosphorescence, and delayed fluorescence of a-PhVPh emitted predominantly from the phenanthryl chromophores in the VPh monomer units, indicating that energy transfer occurs from the PhMMA units to the VPh ones in both singlet and triplet states. In addition, the delayed fluorescence was the most intensive for a-PhVPh. A neglected amount of energy trap sites and an increased density of chromophores in the polymer chain may allow the long-distance triplet–triplet annihilation in this polymer. However, its high molecular weight, which would increase the probability of multiple excitations, was found to be the most important factor for the enhanced delayed fluorescence.

Alternating copolymers consisting of arylalkyl methacrylates. II. Effect of coil collapse on fluorescence spectra of alternating copolymers of 2‐(9‐carbazolyl)ethyl methacrylate and aromatic vinyl monomers

Alternating and random copolymers of 2-(9-carbazolyl)ethyl methacrylate with aromatic vinyl monomers were synthesized and their fluorescence properties were compared in good and poor solvents. Contraction of the polymer coils induced the hypochromic effect, i.e., the mutual interaction of the ground-state chromophores, but caused little quenching of their excited state. This is sharp in contrast with the vinyl-type of polymers, exhibiting large interactions in both the ground and excited states. Introduction of bulky groups on the comonomers in the alternating copolymers further suppressed these interactions.

ALTERNATING COPOLYMERS CONTAINING AN AROMATIC CHROMOPHORE IN EVERY MONOMER UNIT. 2. EXCIMER FORMATION AND INTRAMOLECULAR ENERGY MIGRATION IN ALTERNATING COPOLYMERS OF NAPHTHYLALKYL METHACRYLATE AND VINYLNAPHTHALENE

A series of alternating and random copolymers of 2-naphthylal-kyl methacrylates (NpMMA and NpEMA) and 2-vinylnaphtha-lene (VNp) were synthesized, and their fluorescence properties in tetrahydrofuran (THF) were compared. All of the alternating copolymers containing NpMMA or NpEMA showed a weak ex-cimer emission, indicating that excimer formation between naph-thyl (Np) chromophores in the alternating methacrylate sequences cannot be perfectly inhibited. No distinct difference in the fluorescence from the NpMMA and VNp moieties in poly(NpMMA-alt-VNp) (a-NpVNp) suggests that practically the same chromophores are aligned along the whole polymer chain. This observation is sharp in contrast with the corresponding phenyl polymers exhibiting different spectral features. Fluorescence quenching studies, however, showed no enhancement of the quenching efficiencies for a-NpVNp among the pres-ent polymers. Therefore, energy migration between the nearest-neighboring Np chromophores would inefficiently occur, though this polymer has the highest density of chromophores.