The Relevance of the Collaborative Effect in Determining the Performances of Photorefractive Polymer Materials

Abstract

A derivative of 2-methylindole, 3-[2-(4-nitrophenyl)ethenyl]-1-allyl-2-methylindole, NPEMI-A, is studied for its photoconductivity and photorefractivity behaviour. Its blends with the organic polymer poly-(2,3-dimethyl-N-vinylindole), PVDMI, are also investigated. Due to the expected and devised mutual solubility of the two components of the blends, it is possible to carry out measurements with the weight percent of the chromophore NPEMI-A changing from zero to 100. Films were produced by a squeezing process between two ITO-covered glass sheets. No opacity phenomena, that are so common for many other organic blends due to the segregation of the dissolved chromophore, are observed. The photorefractive optical gain Gamma(2) is obtained as a function of the chromophore content. Differential scanning calorimetry measurements (DSC) are also carried out to obtain the whole change of the glass transition temperature T(g) as a function of the amount of chromophore contained in the blends. From the experimental trend of T(g) a meaningful quantitative estimate of the value of the electrostatic interactions acting in the studied blends, is obtained. The importance of the value of T(g), and of the electrostatic interactions, in determining the extent of the photorefractivity is clearly evident. The results are compared for NPEMI-A (Gamma(2) = 210 cm(-1)) and for NPEMI-E (Gamma(2) approximately = 2000 cm(-1)) that has a N-2-ethylhexyl group instead of a N-allyl group. The Pockels and Kerr contributions and--for the first time--a "collaborative effect" of the photorefractivity of NPEMI-A are distinguished and quantitatively evaluated.

A Convenient Synthesis of Benzonitriles via Electrophilic Cyanation with N‐Cyanobenzimidazole

“… Structure of photorefractive chromophores: 44 MNPAA,170 45 DMNPAA,62 46 DMNPAPOE,171 47 DMNPAPBE,171 48 DMNPAPhBUE,171 49 7‐DCST,46 50 PDCST,29, 46 51 AODCST,46 52 DEANST,115 53 F‐DEANST,82, 162 54 DB‐IP‐DC,172, 173 55 NPEMI‐A,174 56 NPEMI‐E,174, 175 57 H1,176 58 H2,176 59 DANS,168, 165 60 DBA‐TCP,177 61 DBP‐TCP,177 62 IDOP‐20,162 63 ATOP‐1,162162166, 178 64 ATOP‐4,162, 179 65 DHADC‐MPN,86, 180 66 ,181 67 181…”

Organic Photorefractive Materials and Applications

“…[ 174 ] This effect was found to affect both the photoconductive and PR behavior of the materials. Very high values for the gain coeffi cients were found, Γ = 210 cm − 1 for NPEMI-A (99 wt.%) at E ext = 75 V μ m − 1 and Γ = 2027 cm − 1 for NPEMI-E (90 wt.%) at E ext = 90 V μ m − 1 (all at 685 nm).…”

“…[ 196 ] A feature article on this matter can be found in. [ 197 ] An interesting variation of weight contents of low molecular weight glass forming multifunctional chromophore and a poly meric hole-conductor and thus a transfer from composite to LMW-material was recently described for NPEMI-A and NPEMI-E in [ 174 ] and, [ 175 ] respectively. Here, as both 2-methylindole-derivatives show a high mutual solubility in PVDMI ( 3b ,see Figure 4 ) due to their structural similarity, composite samples of chromophore content between 0% and 99% chromophore (each material was doped by 1 wt.% TNFM sensitizer) were fabricated.…”

“…Furthermore, these issues tend to aggravate in light of the higher polarity of optimized ( μ 2 δ a) chromophores with regard to traditional ( μβ ) chromophores (see Table 4 ). [ 170 ] 45 DMNPAA, [ 62 ] 46 DMNPAPOE, [ 171 ] 47 DMNPAPBE, [ 171 ] 48 DMNPAPhBUE, [ 171 ] 49 7-DCST, [ 46 ] 50 PDCST, [ 29,46 ] 51 AODCST, [ 46 ] 52 DEANST, [ 115 ] 53 F-DEANST, [ 82,162 ] 54 DB-IP-DC, [172,173] 55 NPEMI-A, [ 174 ] 56 NPEMI-E, [ 174 , 175 ] 57 H1, [ 176 ] 58 H2, [ 176 ] 59 DANS, [ 168 , 165 ] 60 DBA-TCP, [ 177 ] 61 DBP-TCP, [ 177 ] 62 IDOP-20, [ 162 ] 63 ATOP-1, [162,166,178] 64 ATOP-4, [ 162,179 ] 65 DHADC-MPN, [86,180] 66 , [ 181 ] 67 .…”

“…the 1:1 wt.% eutectic mixture of DMNPAA and MNPAA, [ 170 ] or a 4:1 mixture of DBDC/7-DCST, [ 184 ] ) or incorporating chromophores of high structural similarity with the respective photoconducting host. [ 174 ] Alternatively, in order to reduce the tendency of the dipolar chromophores to form anti-parallel aggregates, a Hamilton receptor is employed to a merocyanine dye. [ 182 ] This substituent is attached to facilitate the formation of head-to-tail parallel ordered chromophores through multiple hydrogen bonds with the barbituric acid electron accepting group on the tail of a second dye.…”