Photosensitization Of Carbazole Based Dyesfor Visible Light Photopolymerization

To enhance the absorptivity in the range visible region dye based photosensitizers were synthesized and applied in the visible light photoinitiating systems,but it is always bring up as interesting topic to be attend in organic synthesis laboratories.Carbazole is known as a robust and a useful aromatic compound to design and synthesize various types of functional dyes.To obtain novel photosensitizers for the visible light photopolymerization and to evaluate the effects of conjugation and structural variations on the properties of compounds eight different carbazole based dyes were synthesized.The obtained dyes consist of two main parts:the first part was designed on the basis of extending conjugation with a couple of side chains,including carbazoleacetylene and phenylacetylene moieties;the second part was concerned with the functional aldehyde and cyanoacetic acid groups attached to carbazole based dyes.They were 2-((9H-carbazol-3-yl)ethynyl)-9-ethyl-9H-carbazole(MEC),3,6-bis((9-ethyl-9H-carbazol-2-yl)ethynyl)-9H-carbazole(DEC),3-(phenylethynyl)-9H-carbazole(MPC)and 3,6-bis(phenylethynyl)-9H-carbazole(DPC),6-((4-(diphenylamino)phenyl)ethynyl)-9-ethyl-9H-carbazole-3-carbaldehyde(CCC),9-ethyl-6-((9-ethyl-9H-carbazol-3-yl)ethynyl)-9H-carbazole-3-carbaldehyde(TCC),(E)-2-cyano-3-(9-ethyl-6-((9-ethyl-9H-carbazol-3-yl)ethynyl)-9H-carbazol-3-yl)acrylic acid(CCN)and(E)-2-cyano-3-(6-((4-(diphenylamino)phenyl)ethynyl)-9-ethyl-9H-carbazol-3-yl)acrylic acid(TCN).The sonogashira coupling reaction was applied to synthesize MEC,DEC,MPC,DPC,CCC and TCC,furthermore CCC and TCC were reacted under Knoevenagel reaction to obtain CCN and TCN.The photosensitizing dyes were characterized by 1H NMR,13C NMR and IR technology.The dye's structures were optimized by quantum chemistry calculation and molecular frontier orbital analysis using density functional theory techniques with Guassianview software,and found that upon achieving coplanar-conjugated molecular structure,these conjugated compounds promote intramolecular charge transfer.During optimization,these structures were found very undeviating and uniform in shape.To identify the optical properties,including UV-vis absorption and fluorescence emission,were performed and theoretical study was also attended.By varying in structures and extending the conjugation with exchanging carbazoleacetylene and phenylacetylene moieties in alkynylcarbazole based single and double substituted dyes and carbazole based aldehyde and cyanoacetic functional groups,those obtained photosensitizing dyes showed a broad absorption above 200nm and tailed to the visible region.In the fluorescence spectroscopy analysis,the alkynylcarbazole dyes exhibit the blue-violet fluorescence emission as of 350 nm to 450 nm,and the largest emission peaks were red-shifted by adding a number of conjugated acetylene structures and the degree of ? delocalization in dyes.Theoretical studies based on optimized geometries showed that all compounds has intramolecular charge-transfer(ICT)ability,moreover,the charge transfer of aldehyde based compounds was found stronger than cyanoacetic acid based compounds.The comparative study of theoretical UV-vis spectra and vertical excitation energies with experimental UV-Vis spectra was done as well.The theoretical data were in agreement with experimental data.To investigate the photosensitization properties,the obtained dyes with iodonium salt(ONI)as the photoinitiation systems was employed for ring-opening cationic polymerization of epoxides(E-51)and free radical polymerization of acrylates(TPGDA)under halogen light source and laser diodes source with a wavelength of 455nm,respectively.It was found that these carbazole based dyes can be beneficial as the photo sensitizer part in visible light photoinitiating systems.It was obtained that structural variation based on conjugation and functional group may effect on properties,as carbazoleacetylene moieties were achieved better than phenylacetylene,and cyanoacetic acid functionalized dyes acquired superior than aldehyde functionalized dyes.The free energy change AGet for the electron transfer between the excited dyes and ONI was calculated from the classical Rehm-Weller equation and the results showed that the photo electron transfer process between the singlet excited dyes and ONI was thermodynamically favored as the calculated AGet values were all negative.On the basis of data obtained by optical analysis,redox potential experiments,fluorescence quantum values,free energy change AGet values,steady state photolysis and double bond and epoxy conversions a reasonable mechanism was proposed based on the photo electron transfer process related to the reaction of excited dyes with ONI.Moreover,by considering these properties,these dyes would have some suspected applications in the fields of photopolymerization under visible light photoinitiating system.