tained over macroscopic film thicknesses and large surface areas by vapor deposition of a single molecular species on an amorphous substrate. Inducing the non-centrosymmetric order by using selective hydrogen bonding to the substrate and between the molecules leads to a much better molecular ordering than with the technique described by Cai et al., [13] which requires control of the molecular beam direction relative to the substrate. The present technique does not require a well-defined molecular beam, and is also much simpler and faster than the synthetic methods used by Ulman [7] and Marks and Ratner [18] or for LB films.It is important to note that the alignment in our films is critically dependent on the ability of these molecules to selectively hydrogen bond to the surface, in order to begin the alignment process, and selectively hydrogen bond to itself in a unidirectional fashion in order to maintain the alignment over a large thickness. We have carried out preliminary experiments with molecules that only posses hydrogen bond acceptors and, therefore, can form hydrogen bonds to the substrate surface, but which lack hydrogen bond donors thus eliminating the possibility of intra-molecular hydrogen bonding, and have shown that only very thin films (of the order of a few monolayers thickness) with polar ordering perpendicular to the substrate surface can be grown. As the films grow thicker, we see that the ordering cannot be maintained.In conclusion, we have shown a simple and efficient new method to produce supramolecular self-assembled thin films with well-defined polar ordering perpendicular to the substrate surface. The resulting films are homogenous over a large area, and a regular, deterministic molecular ordering can be maintained over a large thickness of the order of 1 lm. The fact that the films were grown on amorphous glass substrates circumvents the need for surface epitaxy. The quality of the films and the simplicity of the fabrication method make this novel technique very attractive for the fabrication of nonlinear optical waveguides for frequency conversion or electrooptic modulation. Despite the relatively low nonlinearity (d 111 = 5 pm V ±1 ) that has been obtained in this first demonstration, the high degree of molecular ordering and the fact that the films consist of only one component make them potentially very interesting when compared to present candidates for organic electro-optic modulators, poled polymers. The higher degree of order and tighter molecular packing in our films should also lead to a better photostability when compared to amorphous systems with embedded chromophores. A further detailed investigation of the mechanism that leads to the molecular ordering and an optimization of the growth conditions should lead to a new generation of organic waveguides for frequency conversion and electro-optic modulation. Experimental.BITINPH was purchased from Opto-Organics Industrial Research Limited and purified by recrystallization from ethanol. The amorphous glass substrates were cl...

We have carried out a femtosecond transient absorption spectroscopic study on nickel(II) porphyrins in various solvents in order to obtain detailed information on vibrational relaxation processes occurring in the initial stage after photoexcitation to the highly excited states. We found the decay process of time constant of approximately 1 ps corresponding to the intramolecular vibrational relaxation process for Ni(II)TPP and Ni(II)OEP in toluene. In addition to this process, the intermolecular vibrational relaxation process with 10−20 ps lifetime was also observed for Ni(II)OEP in toluene, although its contribution to the overall decay process is relatively weak probably due to the weak solute/solvent interaction. In coordinating solvents such as pyridine and piperidine, we observed the intramolecular vibrational relaxation processes before complete population of the bottleneck excited metal 1|0,d z 2 〉 or 3|0,3(d,d)〉 state. In this case, it is likely that the intermolecular vibrational relaxation process associated with photodissociation/photoassociation processes depending on the selective excitation of four- and six-coordinate species is accompanied by the intramolecular vibrational relaxation due to the strong solute/solvent interaction. These processes are also believed to be responsible for the excess energy dissipation of highly excited nickel(II) porphyrins into the surrounding solvent molecules.

Although significant progress has been made in the development of vacuum‐deposited small‐molecule organic light‐emitting diodes (OLEDs), one of the most desired research goals is still to produce flexible displays by low‐cost solution processing. The development of solution‐processed OLEDs based on small molecules could potentially be a good approach but no intensive studies on this topic have been conducted so far. To fabricate high‐performance devices based on solution‐processed small molecules, the underlying nature of the produced films and devices must be elucidated. Here, the distinctive characteristics of solution‐processed small‐molecule films and devices compared to their vacuum‐deposited counterparts are reported. Solution‐processed blue OLEDs show a very high luminous efficiency (of about 8.9 cd A–1) despite their simplified structure. A better hole‐blocking and electron‐transporting layer is essential for achieving high‐efficiency solution‐processed devices because the solution‐processed emitting layer gives the devices a better hole‐transporting capability and more electron traps than the vacuum‐deposited layer. It is found that the lower density of the solution‐processed films (compared to the vacuum‐deposited films) can be a major cause for the short lifetimes observed for the corresponding devices.

The photoinduced energy transfer processes in 1,4-phenylene-, 1,3-phenylene, 1,2-phenylene, and 4,4‘-biphenylene-linked and directly-linked Zn(II)-free base porphyrin heterodimers in THF were investigated by femtosecond transient absorption spectroscopy. The energy transfer rates were compared between TPP-type and OEP-type heterodimers respectively as A2u-HOMO and A1u-HOMO subunits, for evaluating the relative contribution of the through-bond and through-space interactions. The rate difference becomes smaller with a decrease of spacer, more than 10 for 1,4-bis(phenylethynyl)phenylene and 1,4-diphenylethynylene, 4 for 4,4‘-biphenylene-linked heterodimer, and 3 for 1,3- and 1,4-phenylene-linked spacers. In the meso−meso directly-linked case, the energy transfer rates are the same ((0.55 ps)-1) for 5,5,15,15-tetrakis(3,5-bis(octyloxy)phenyl)-substituted and 5,5,15,15-tetrakis(pentafluorophenyl)-substituted heterodimers, featuring only a minor influence of the frontier orbital characteristics on the energy transfer rate. The energy transfer rates are identical (0.55 ps)-1 for the directly-linked meso−meso heterodimers substituted with 3,5-bis(octyloxy)phenyl and pentafluorophenyl groups regardless of the difference in the HOMO orbital symmetry characteristics, suggesting the predominant Coulombic interaction for the energy transfer in these close proximity porphyrin dimers. In the case of 1,2-phenylene-linked heterodimers, the choice of the peripheral substituents can lead to a state-to-state rapid energy transfer with a rate of (0.55 ps-1) for the TPP-type model or a delocalized excimer-like diporphyrin excited state for the OEP-type model. Collectively, these results indicate that even for the covalently-linked models the relative contribution of the through-space Coulombic interaction becomes increasingly important upon the decrease of the center-to-center separation. Especially, the fast and efficient energy transfer occurring in the directly-linked heterodimer illustrates that this porphyrin unit can be utilized as a good candidate for energy transfer functional arrays in molecular photonic devices.

A highly loaded ZnS nanoparticle (NP) array within mesoporous channels was prepared by repetitive insertion of ZnS reverse micelles. Contrary to the ZnS NPs in the water pool of reverse micelles exhibiting blue emission, the ZnS NPs incorporated within the organically functionalized mesoporous channels showed the emission in the ultraviolet region with a single recombination lifetime of 1.3 ± 0.2 ns. Such optical characteristics are considered to dominantly originate from the potential traps of lattice sulfur vacancies existing in the confined ZnS NPs within the fit size of the functionalized host pore channels.