Molecular Design Of Polycyclic Aromatic Hydrocarbon And N-heterocyclic Two-photon Absorption Materials

Two-photon absorption (TPA) materials have attracted considerablyincreasing interest with the emergence and advancement of the laser technique.Up to date, they can be explored in the fields of chemistry, physics and biology.Especially, their potential applications in biology society are of great importance,such as three-dimensional photolysis release, two-photon biological labeling,two-photon fluorescence imaging (TPFM). Indeed, the practical TPA materialsare still limited, so further designing and synthesizing new materials withexcellent TPA properties are urgent. To construct and select TPA molecules withlarge TPA cross sections (δmax), we have systematically studied several importantTPA chromophores including polycyclic aromatic hyrocarbon built into graphenenanoribbons (GNRs) and heterocyclic compounds by means of the quantumchemistry calculation in the thesis. Then, the structure-property relationshipshave been revealed and lay the guidelines for both spectra tuning andamplification of molecular TPA in the target region. Our investigations provideuseful and valuable information for future experiment study on the design andsynthesis of novel chromophores with intense TPA response, and enrich TPAmaterials.The main researches are summarized as follows:1. A Comparative Study of One-and Two-Photon Absorption Propertiesof Pyrene and Perylene Diimide DerivativesTwo important classes of organic molecules, perylene diimide (PDI) andpyrene derivatives built into GNRs have been found to possess relatively excellentphotophysical and photochemical properties and especially high δmax. However,there are significiant differences between their one-and two-photon absorptionproperties. Herein, these properties of some novel PDI and pyrene derivativeswere comparatively investigated by the DFT and ZINDO methods. The calculatedresults indicate that with respect to PDI derivatives, the δmaxvalues for pyrenecompounds increase obviously, the maximum peaks of OPA and TPA spectra are blue-shifted. The different π-conjugated bridges (fluorene and pyrene) andterminal groups have slight effect on the OPA properties. Moreover, the δmaxvalues of molecules with benzothiazole-substituted terminal groups are larger thanthose of the molecules with diphenylamine. Furthermore, the molecular size hasmarked effect on OPA and TPA properties. It is worthy to mention that cruciform8displays the largest δmaxamong all the studied molecules in the near-infrared(NIR) region, implying its potential use as the TPA fluorescent labeling material.2. Theoretical prediction of two-photon absorption properties ofN-annulated quaterrylenes as near-infrared chromophoresGraphene nanoribbons have attracted increasing attention due to highpotentiality in nanoelectronics. In the present study, quantum-chemicalcalculations of structural and nonlinear optical properties have been first carriedout for the nanoelectronical materials, a new series of ladder-type N-annulatedquaterrylenes and their imide chromophores. The effects of the solvent terminalgroups, the number of N-annulated bridges and π-conjugated length are discussedin detail. The OPA and TPA properties of the two series of DI and N-MImolecules show a clear solvent dependence due to the carboximide substitutionfeaturing larger polarization. Introducing electron-donating groups anddicarboximides, as well as increasing the conjugated length lead to red-shifts ofthe OPA, emission, and TPA spectra, lower emission lifetimes, and enhanced TPAcross sections, but further extension of the conjugated framework does notalways promote an increase of δmax. By adding one N-annulated bridge at the bayposition both on the short and long axis, the TPA spectra are red-shifted and theδmaxvalues decrease in chloroform. The changing trends of δmaxcan be explainedby the transition moment and the intramolecular charge transfer.3. Nonlinear Optical Properties for a Novel Class of Self-assembledHexa-peri-hexabenzocoronene ChromophoresThe systematic investigation of the linear and nonlinear optical properties onsuch a novel class of self-assembled of hexa-peri-hexabenzocoronene (HBC)chromophores is of great importance for rationally designing two-photon absorption materials. The results indicate that all chromophores exhibit anintense absorption in the UV/Vis blue-green region. Increasing the strength ofelectron-donating or-accepting terminal groups leads to significant bathochromicshifts of the absorption band and enhancement of the TPA cross section. For themolecules featuring–CF3and–CN groups at the terminal end, replacement of adouble bond by a triple bond in conjugated linker results in the increase of δmax,owing to the lower bond-length alternation and the better robustness ofphenylene-ethynylene. The TPA spectra are red-shifted and the δmaxvalues areenhanced as the number of branching increases. The solvent results slightly affectthe TPA properties of the molecules with the fluorinated methylene and cyanosubstituents. Thus, a solvatochromism effect has a positive influence on the TPAresponse of the molecules with nitryl moieties, which is ascribed to the nitromoiety bearing the higher electro-negativity that can result in larger polarization.A linear relationship between the first hyperpolarizability and the TPA crosssection is observed.4. Theoretical investigation of two-photon spectra of pyrazabole(pyrazole aluminum) chromophoresAn extensive series of pyrazabole chromophores containingpseudo-conjugated systems have been theoretically constructed and investigatedon the OPA and TPA properties by using DFT and ZINDO methods. The resultsindicated that all the pyrazabole chromophores show strong OPA at around400nm and intense TPA properties in the range of500–600nm with δmaxas large as540–3560GM, which are excellent candidates for optical power limitingmaterials. It is noteworthy that PA3and PAF2exhibit large δmaxin the NIRregion, indicating that they may be particularly attractive as probes fortwo-photon fluorescence imaging. The influence of incorporating electronacceptors in the central core, π-conjugated bridge and terminal groups on OPAand TPA properties was analyzed in detail to derive structure-propertyrelationships and to lay the guidelines for both spectral tuning and amplificationof molecular TPA in the target region. Meanwhile, the solvent effects on these properties were taken into account within the PCM model. The solvent has asignificant impact on the TPA properties for chromophore PA3and leads to theTPA spectra (λTmax) red-shift and δmaxenhancing relative to those in gas phase.In addition, from the calculations of pyrazole aluminum molecules, we candraw the conclusion that the compounds with the Al2N4center behave in asimilar manner to pyrazabole chromophores in terms of linear optical, and TPAproperties and they possess an increased δmaxto some extent.5. Theoretical insight into two-photon absorption for a series ofN-arylpyrrole-based derivativesThe N-arylpyrrole-based dyes possessing excellent opto-electronicproperties are promising candidates for two-photon fluorescence labelingmaterials. The systematic investigation of the geometric and electronic structuresas well as linear and nonlinear optical properties on them is important for bothfine-tuning electronic spectra and TPA cross sections. We thoroughly studied theinfluence of the π-conjugated center and N-substituted pyrrole moieties on OPAand TPA properties. The results show that introducing N-arylpyrrole moietiesproduces bathochromic-shifts of the absorption and emission bands, as well as anenhancement of δmax, denmonstrating that the electron-rich pyrrole moieties canefficiently increase ICT. Substitution of the fluorenyl core with benzothiadiazoleproduces lower energy gaps, higher emission lifetime, red-shifts of OPA and TPAspectra, and larger δmax. The UV/Vis absorption and emission bands are highlydependent on the nature of the active building blocks. The aromatic ringsattached to pyrrole through the C–N single bond can modulate the absorption inthe high energy range and thus subtly modify the electronic properties.Incorporating boron-dipyrromethene units at the R positions leads to theenhancement of δmaxdue to the strong ICT.