Chromophore Design for Photorefractive Organic Materials

• Published in: Chemphyschem 2002-01, Vol.3 (1), p.17-31
• Main Authors: Würthner, Frank, Wortmann, Rüdiger, Meerholz, Klaus
• Format: Article
• Language: English
• Subjects: chromophores; Exact sciences and technology; Fundamental areas of phenomenology (including applications); holography; nonlinear optics; Optical materials; Optics; Other nonlinear optical materials; photorefractive and semiconductor materials; photorefractivity; Physics; Polymers and organics; supramolecular chemistry
• ISSN: 1439-4235; 1439-7641
• DOI: 10.1002/1439-7641(20020118)3:1<17::AID-CPHC17>3.0.CO;2-N

During the last years, significant progress has been achieved in understanding the mechanism of the photorefractive effect in amorphous organic materials. New chromophores could be devised which provided a substantial increase in the electrooptical response and lead to photorefractive materials with unprecedented refractive index modulation (Δn=10−2 at E=28 V μm−1) and two‐beam coupling gain. These improvements could only be accomplished by optimizing the electronic structure of highly conjugated merocyanine dyes to perfectly balanced dyes in the charge resonance limit (such as aminothienyl oxopyridone (ATOP) and indoline dimethine oxopyridone (IDOP) derivatives), considering effects of supramolecular ordering (dipolar aggregation), and adjusting the compatibility of the dyes to photoconducting polymers (like poly‐N‐vinylcarbazole). In particular, optimized glass‐forming dyes (such as 2BNCM and ATOP‐4) combine the dual functionalities of charge transport and electrooptical response and exhibit photorefractivity even in absence of any additional photoconductor. A masterful optimization of the molecular, supramolecular, and morphological characteristics of electrooptical chromophores is necessary to create advanced photorefractive polymers and low molecular weight organic glasses. Glass‐forming dyes with large dipole moments and highly polarizable π‐systems, like the merocyanine shown in the formula, afford unprecedented refractive index modulation and two beam coupling efficiencies.