Search results for "Chromophore"
showing 10 items of 309 documents
Chapter 2 Single molecule spectroscopy of multichromophoric dendrimers at room and liquid helium temperatures
2004
Publisher Summary This chapter discusses the single molecule spectroscopy of multichromophoric dendrimers at room and liquid helium temperatures. Single molecule spectroscopy has become an important tool for the optical study of the electronic interactions of proximate chromophores as the electronic interactions can be studied without averaging over the properties of an intrinsically heterogeneous ensemble. Single perylenemonoimide (PMI) chromophores are selectively addressed in the frequency domain within spatially isolated multichromophoric dendrimers, which are dispersed in a polymer film. Although the chromophores are interacting, they still can be addressed separately. This feature in …
The Role of Planarity versus Nonplanarity in the Electronic Communication of TCAQ-Based Push–Pull Chromophores
2018
Donor-acceptor-substituted alkynes, endowed with 11,11,12,12-tetracyano-9,10-anthraquinodimethane (TCAQ) and N,N-dimethylaniline (DMA) units, have been further functionalized by a [2+2] cycloaddition with tetracyanoethylene (TCNE) followed by a subsequent retro-electrocyclization to form distorted nonplanar structures with bridging 1,1,4,4-tetracyanobuta-1,3-diene (TCBD) units. Comprehensive spectroscopic, electrochemical, and computational studies have been carried out to compare the electronic communication in planar (alkyne bridges) and nonplanar (TCBD bridges) TCAQ-based push-pull chromophores. Cyclic voltammetry and UV/Vis absorption measurements confirm the electronic communication be…
Single-Molecule Spectroscopy of MEH-PPV Polymer Molecules in Different Host Matrices
2009
Fluorescence emission and excitation spectra of single MEH-PPV molecules dispersed in three different host polymers (PMMA, PS, and Zeonex) have been recorded at 1.2 K. We observed only minor effects of the host matrix on the following parameters: the ratios of single-chromophoric to multichromophoric emission, the widths of the distributions of emission maxima, and the (generally very low) fraction of emission spectra with sharp zero-phonon lines. The differences are tentatively attributed to different conformations of MEH-PPV chains, subtle variations in local chromophore−matrix interactions, and/or different distributions of conjugation lengths of emitting chromophores, respectively. Usin…
NLO-polymers containingtert-butyloxycarbonyl protecting groups: Modification after processing leading to thermally stable nonlinear optical materials
1997
Dye-containing S∗cside-on/end-on copolymers
1995
Abstract Mesomorphic copolysiloxanes, which combine ‘normal’ end-on linked chiral mesogenic units inducing S∗c phases and side-on fixed chromophores were prepared. The interplay of the different orientational tendencies of these moieties, which are perpendicular (end-on linked mesogenic groups) or parallel (side-on fixed chromophores) to the polymer chain, lead to a strong destabilization of the S∗c phase. However, copolymers with up to about 10 mol % of chromophores still show a smectic C∗ phase. FTIR measurements show that both moieties orient parallel to each other and perpendicular to the polymer chains. These copolymers are interesting to consider as coloured guest-host S∗c materials f…
Second harmonic generation in self-assembled alternating multilayers of hemicyanine containing polymers and polyvinylamine
1995
Abstract Assembly of noncentrosymmetric multilayers is a facile technique for preparing noncentrosymmetric films avoiding electrical poling procedures and problems from subsequent relaxation of the induced orientational order. A maximum Xzzz of 13 × 10−9 esu was achieved for the assembly of up to six layers. Current problems are the long-term hydrolysation of the hemicyanine nonlinear optical chromophores and the reduction of polar orientation with increasing layer thickness.
One is Enough: Influencing Polymer Properties with a Single Chromophoric Unit
2011
1) Institute for Technical and Macromolecular Chemistry, University of Hamburg, Bundesstrasse 45, D-‐20146 Hamburg, Germany 2) WCU program of C2E2, School of Chemical and Biological, Engineering, College of Engineering, Seoul National University, Seoul, Korea Designing a polymer usually involves the incorporation of multiple functional units into a polymer chain, which mutually determine the polymer properties. By combining various functional units, a myriad of polymer properties can be fine-‐ tuned. Classical polymer chemistry teaches us that a single functional group -‐-‐ in particular the end-‐group of a polymer chain -‐-‐ does not contribute to the polymer properties, as is indee…
New Figure of Merit for Tailoring Optimal Structure of the Second Order NLO Chromophore for Guest-Host Polymers
2008
Reliability to forecast SHG efficiency using two sets of non linear optical (NLO) chromophore figures of merit (FOM) was tested. One of them predicts that SHG efficiency d 33 of the poled guest-host polymer is proportional to ground state dipole ∼ μg, another to ∼ 1/μg. Correlation of maximal achieved second order NLO efficiency of the PMMA based systems containing eight dimethylaminobenzylidene-1, 3-indandione (DMABI) related chromophores with proposed FOM have been analyzed. The best correlations were obtained with second set of FOM, especially if high dipole moment (μg > 7D) chromophores are included in analysis.
Poling dynamics of an EO active material using parallel-plate electrodes
2017
We describe the sample preparation and experimental setup for second harmonic generation measurement of electro-optical (EO) chromophore/polymer system at the time of contact-poling. Different types of spacers for avoiding electric breakdown due to avalanche multiplication are compared. Electric field threshold values for second harmonic generation are observed in all samples.
Design and Optimization of Chromophores for Liquid Crystal and Photorefractive Applications
1999
ABSTRACTOrganic chromophores have been exploited for a wide range of discrete optical and electronic functions as well as a growing number of combined opto-electronic functions. We are pursuing development of organic and polymer materials for a range of applications that require properties including liquid crystallinity, second order optical nonlinearity, photorefractivity and, more recently, special nonlinear optical behavior involving molecular chirality.