L. Gerca

Reversible trans/cis photoisomerization in Langmuir-Blodgett multilayers from polyfunctional azobenzenes

Abstract Four novel, amphiphilic, N -acylaminoazobenzene derivatives containing a sulfonyl group and a β-alanine moiety were synthesized and their mono- and multilayers were prepared by the Langmuir-Blodgett (LB) technique. The opto-physical properties of the LB multilayers were investigated. Some relationship between the chemical structure of the azobenzenes and photosensitivity of their LB multilayers has been found. Reversible trans/cis photoisomerization was observed on alternate irradiation with ultraviolet and visible light of LB multilayers from azobenzenes modified by the introduction of a second aliphatic chain in the N -acylamino fragment as well as by introduction of the bulky N,N′ -dicyclohexyl urea moiety.

Optical properties of some novel azobenzenes in thin layers

We have synthesized and investigated a novel electrondonor -- electronacceptor type photoactive amphiphilic azobenzene derivative containing the hydrophobic dicyclohexylamine moiety along with the hydrophylic carboxyl group at the opposite end of the molecule. Reversible trans/cis photoisomerization of this compound in solutions and in Langmuir-Blodgett multilayers has been observed on irradiation with alternating UV (360 nm) and visible (450 nm) light. The reversible changes of absorbance of main absorption band and surface potential of Langmuir-Blodgett multilayers on alternate irradiation is demonstrated.

Optically induced switching of dicyclohexylamino substituted azobenzene derivatives in thin ordered films

During the last years, there has been an increasing interest in the photoinduced switching effects. Among the objects of concern azobenzene derivatives, isomerizing under UV and visible light, occupy a prominent position. To understand the photoresponse of these materials in the condensed phase, their spectroscopic and electrical properties are studied. It is shown that the photoresponse depends on the orientation of the molecules and their packing. A number of novel azobenzene derivatives containing a N,N-dicyclohexyl sulfonamide moiety is synthesized. The derivatives differ in the length of alkyl chains between the azobenzene moiety and SH or COOH groups. The morphology and the photoinduced switching of the surface potential of the self-assembled monolayers and Langmuir-Blodgett multilayers are investigated.

PV Effect of Fullerene/Poly(3-Hexylthiophene) Blend Sensitized By Phthalocyanine Having Infrared Absorption Ct Band

An attempt was made to extend the photosensitivity spectral range of fullerene/poly(3-hexylthiophene) blend to NIR region by adding extra electron donor — hydroxygallium phthalocyanine (GaOHPc) with a strong and wide intermolecular charge transfer (CT) band around 830 nm. Multilayer cells of ITO/PEDOT: PSS/6 GaOHPc/P3HT: C61(CO2Et)2 have been prepared by spin coating with vacuum evaporated Al or In top electrodes. Significant photosensitivity of the cells was in 370–900 nm spectral range. However charge carrier photogeneration efficiency was 3 times higher for illumination in P3HT absorption band as compared with the GaOHPc CT band at 830 nm. But when GaOHPc was mixed in the blend forming P3HT:C61(CO2Et)2:GaOHPc active layer its CT band shifted to infrared part at 875 nm. At the same time the charge carrier photogeneration efficiency for illumination in GaOHPc CT band increased significantly, exceeding its value for illumination in P3HT absorption band.

Amide or sulfonamide groups containing azobenzenes for Langmuir - Blodgett films

Five amphiphilic alpha- or beta-amino acid derivatives containing photoactive azobenzene moiety and bearing amide or sulfonamide functional groups were synthesized and mono- and multilayers, prepared by Langmuir-Blodgett technique, were investigated. The reversible photoisomerization processes in solutions of these derivatives were observed. Reversible trans/cis photoisomerization of 4-[4-(hexyl- palmitoylamino)- phenylazo]benzenesulfonyl-(beta) -alanine in multilayer assemblies has been observed on alternate irradiation with UV light (centered at 360 nm) and visible light (452 nm).