Theoretical Study On One- And Two-photon Absorption Of Covalent Hybrid Materials Based On Graphene And Small-molecule Fluorescent Probes

In recent years, with the development of laser technology, two-photon absorption(TPA) phenomenon has attracted more and more attention. Because the TPA materials and two-photon fluorescent probes with excellent TPA properties are widely used in biology, chemistry and physics and other fields, especially their potential applications in biology society field have aroused great interest in research, such as two-photon fluorescence imaging, biological labeling, photodynamic therapy and so on. But so far, the ideal and practical TPA material and fluorescent probe are very limited, so it is urgent to design and develop materials with outstanding two-photon absorption properties. Thus, we have systematically proposed some effective designed strageties towards a series of covalently functionalized hybrid materials based on graphene from the theoretical chemistry perspective by using quantum chemistry calculation methods. Moreover, apart from the TPA materials, we also have designed and investigated a series of two-photon nitric oxide(NO) fluorescent probes and the corresponding reaction products based on boron dipyrromethene(BODIPY). Moreover, a series of novel two-photon fluoride ion(F–) probes and the related reaction products on the basis of diketopyrrolopyrrole(DPP) are also designed, to investigate their one- and two-photon absorption properties. Then, we develop several two-photon fluorescent probes for thiophenols on the basis of both PET and TBET processes, using both BODIPY and DPP to study their OPA and TPA properties. Our calculated results further reveal the molecular structure-property relationships and regularity, and provide a useful theoretical basis for the design and synthesis of novel materials and fluorescent probes with excellent TPA properties.The main studies are summarized as follows: 1. Theoretical investigations on one- and two-photon absorptions for a series of covalently functionalized hybrid materials based on grapheneIn this work, a series of novel graphene-like molecules and their corresponding hybrids with porphyrin have been designed. The calculated results reveal that the hybrid molecules possess a higher TPA response resulting from intramolecular charge transfer, compared with their counterparts without a porphyrin. The maximum TPA cross sections(?TPA) calculated by the ZINDO method are as large as 913.0–3904.3 GM. The calculated results indicate that the designed compounds with large TPA cross-sections have potential for applications involving optical limiting and two-photon fluorescence microscopy(TPFM). We expect that this study will provide a theoretical perspective for designing novel TPA materials based on graphene for further applications in the future. 2. Effect of carbon-layer rearrangement on one- and two-photon absorption properties in the alternative graphene-like hybrids– A theoretical investigationIn this work, novel alternative graphene-like hybrids covalent with porphyrin(porphyrin-graphene-like hybrids) are designed, named TPP-gra(n)-a and TPP-gra(n)-b(n = 1 – 5), respectively. Our study shows that the rearrangement of carbon-atom layers of the hybrids can effectively enhance electronic delocalization, bringing about better TPA properties. In addition to the increase of the graphene-like size, substituting porphyrin into different active-carbon of graphene-like molecules can cause obvious differences of the OPA and TPA properties between the two systems, especially the TPA cross sections(?TPA), for the ?TPA values of TPP-gra(n)-b series are much larger than that of corresponding TPP-gra(n)-a compounds, ascribing to their better polarization induced by porphyrin, which results in stronger TPA responses, such as TPP-gra3-b, TPP-gra4-b and TPP-gra5-b, whose ?TPA can be as large as 5686.2 ~ 19496.6 GM ranging from 535.8 to 579.4 nm. The carbon-based materials possessing relatively high ?TPA values have a great potential for applications in optoelectronic devices. 3. A theoretical study of a series of novel two-photon nitric oxide(NO) fluorescent probes based on BODIPYIn this work, a series of novel nitric oxide(NO) probes and the corresponding reaction products are designed based on BODIPY and its devirivative heteroarylfused BODIPY or 3,5-distyryl substituted BODIPY(KFL). Furthermore, the mechanism of recognizing NO controlled by intramolecular photoinduced electron transfer(PET) is verified by theoretical chemistry computation in this work. More importantly, the two-photon absorption properties of these novel chromophores are explored by using DALTON program. The results of our study show that the two-photon absorption cross sections of the designed molecules are as large as 1056.9–39702.5 GM with the wavelengths ranging from 700 to 850 nm, especially KFLs, which have more potential for applications in two-photon absorption fluorescence imaging with larger two-photon absorption cross sections in the near-infrared region, because of their better rigidity and p-conjugation that are more conducive to intramolecular charge transfer. Finally, this work presents structural modified strategies for increasing two-photon response. 4. Theoretical investigation on the one- and two-photon responsive behavior of fluoride ion probes based on DPP and its ?-expanded derivativesBecause of the special physiological and chemical properties of fluoride ion(F–) and its important roles in environment and living organisms, a series of novel F– probes(DPPs) and the corresponding reaction products(DPP-Fs) based on DPP fluorophore and its ?-expanded derivatives, are devised, their electronic structures and one-photon absorption(OPA) are investigated by employing the density functional theory(DFT) and time-dependent DFT(TD-DFT) methods combined with B3 LYP functional, more importantly, their two-photon absorption(TPA) properties are obtained by using quadratic response theory in DALTON program. Our calculated results reveal that the modifications of compounds by both increasing the number of electron-donating groups(thiophene groups) and introducing fluorene units can effectively enhance the TPA responses, making the probes, such as DPP3, DPP4 and DPP5, show relatively higher TPA cross sections(?TPA) in the range of 5380.0 – 9500.0 GM in the near-infrared region(885.6 – 991.9 nm). Moreover, the strategy of modifying compounds by using fluorene(DPP6), aza-BODIPY(DPP7) and BODIPY(DPP8) moieties as ?-expanded central structures, respectively, is proved ideal for obtaining large ?TPA values in longer wavelengths, especially DPP7 and DPP8, whose ?TPA values are about 2 ~ 3 times larger than that of the related DPP-Fs, which is superior to the previously reported two-photon F– probes, for large ?TPA differences between probes and the reaction products are highly desirable for practical two-photon F- detection in biological system. 5. Two-photon fluorescent probes for thiophenols combining both PET and TBET processes from a theoretical perspectiveThiophenols play important roles in industrial production. However, because of their highly toxic, they can cause serous pollution to the environmental and the biological systems. Therefore, it is of great importance to effectively detect thiophenols in both intracellular and extracellular systems. To realize the effective recognition towards thiophenols, we have designed several novel thiophenols probes and the related reaction products based on both through-bond energy transfer(TBET) and “turn-on” photoinduced electron transfer(PET) mechanisms, to study their structure-property relationships using theoretical methods, in particularly the two-photon absorption(TPA) features. The calculated results reveal that our modification strategies by changing energy acceptor and energy donor, who possess excellent TPA properties, can availably increase the TPA cross sections(?TPA) of the reaction products, whose ?TPA values are as large as 921.0 – 2568.8 GM in the range of 789.7 – 908.3 nm, which are conductive to two-photon fluorescence microscopy(TPFM).