Design, Synthesis, Energy Transfer And Photochromic Properties Of Bodipy-containing Spirooxazine And Spiropyran Compounds

Bodipys are interesting materials that are known to show high molar absorptioncoefficients, high fluorescence quantum yields and easy to modification. As a result,they have been utilized as dyes in a variety of different fields, such as in lightharvesting materials, cation sensors, and fluorescence labels. Spirooxazines andspiropyrans are amazing materials that show photochromic and acidochromicproperties. Due to their high fatigue resistance and excellent photostability, theirphotochromic behavior has been extensively studied for potential applications in thedevelopment of molecular switching devices, optical information storage, and variousother applications. There are a number of reports on photochromic behaviour oforganic spirooxazines and spiropyrans, and several photochromicspiropyran-containing Bodipy derivatives are also reported. However, most of themare confined to photo-controlled fluorescence system, with corresponding studies onacid-induced spirooxazine-and spiropyran-containing energy transfer systems beingvery rare. Furthermore, the systematical studies about the photochromic properties ofspirooxazine-and spiropyran-containing Bodipy derivatives are also rare. In thisdissertation, we report the synthesis, energy transfer, and photochromic properties ofspirooxazine-and spiropyran-containing Bodipy derivatives with different types oflinker. Firstly two series of spirooxazine-and spiropyran-containing Bodipy derivativeswith different lengths of oligoether have been designed and synthesized and theirelectrochemical, photophysical and photochromic properties are then investigated.Upon addition of trifluoroacetic acid, compounds2.1–2.3exhibited color changesfrom orange to purple with the growth of a new absorption band at ca.560nm and awell-defined isosbestic point at ca.360nm. Upon excitation at the isosbestic point,the emission intensity is gradually quenched with increasing concentration of TFAfrom10equivalents to40equivalents. The mechanism for fluorescence quenching isproposed to be energy transfer from Bodipy to the ring-opened form of spirooxazineas there is a significant spectral overlap between the absorption spectrum of thering-opened form of spirooxazine and the emission spectrum of Bodipy. Energytransfer is further supported by the lack of fluorescence quenching for compounds2.4–2.6and2.8–2.10upon addition of TFA. In addition, energy transfer is alsosupported by the ultrafast transient absorption data. Upon addition of40equivalentsof TFA, the Bodipy excited state undergoes a faster decay involving multiple decaycomponents and the time constant of the Bodipy excited state reduces significantly.All these results clearly support the quenching of the Bodipy excited state by thering-opened merocyanine and the efficiency of energy transfer doesn’t have anobvious change upon increasing the length of oligoether. Photochromic reaction andthe kinetics for the bleaching reaction of the ring-opened forms of compounds2.1–2.3and2.8–2.10after excitation at355nm have been investigated in acetonitrile by usingUV-vis absorption spectroscopy at various temperatures. By monitoring theabsorbance at620nm for compounds2.1–2.3and565nm for compounds2.8–2.10,the kinetics for the bleaching reactions are investigated and the rate constants andactivation parameters of compounds2.1–2.3and2.8–2.10at various temperatures aremeasured. The results show that the rate of the bleaching reaction of compounds2.8–2.10is much slower than that of compounds2.1–2.3. A systematic investigationon the variation between ΔH≠and ΔS≠in spirooxazine-containing compounds andspiropyran-containing compounds have been performed and find that ΔH≠and ΔS≠ have the same change trend for compounds2.1–2.3and2.8–2.10. An isokineticrelationship, which means a linear proportionality between ΔH≠and ΔS≠, is observedfor compounds2.1–2.3and2.8–2.9, respectively. This is indicative of a commonbleaching reaction mechanism for compounds2.1–2.3and a common bleachingreaction mechanism for compounds2.8–2.10.Secondly a series of spirooxazine-containing Bodipy derivatives with differentlengths of phenylacetylene linker have been designed and synthesized and compound3.1has been characterized by X-ray crystallography. Their electrochemical,photophysical and photochromic properties are then studied. Upon addition oftrifluoroacetic acid, compounds3.1–3.5exhibited color changes from orange topurple with the growth of a new absorption band at ca.570nm and a well-definedisosbestic point, respectively. Upon excitation at the isosbestic point, the emissionintensity is gradually quenched with increasing concentration of TFA from1000equivalents to4000equivalents. The mechanism for fluorescence quenching isproposed to be energy transfer from Bodipy to the ring-opened form of spirooxazineas there is a significant spectral overlap between the absorption spectrum of thering-opened form of spirooxazine and the emission spectrum of Bodipy. Energytransfer is further supported by the lack of fluorescence quenching for referencecompounds3.6–3.8upon addition of TFA. In addition, energy transfer is alsosupported by the ultrafast transient absorption data. Upon addition of4000equivalents of TFA, the Bodipy excited state undergoes a faster decay and the timeconstant of the Bodipy excited state reduces significantly. All these results clearlysupport the quenching of the Bodipy excited state by the ring-opened merocyanine.Photochromic reaction and the kinetics for the bleaching reaction of the ring-openedforms of compounds3.1–3.5and3.9–3.10after excitation at355nm have beeninvestigated in toluene by using UV-vis absorption spectroscopy at varioustemperatures. By monitoring the absorbance at630nm for compounds3.1–3.5and3.9–3.10, the kinetics for the bleaching reactions are investigated and the rateconstants and activation parameters of compounds3.1–3.5and3.9–3.10at various temperatures are measured. The results show that the rate of the bleaching reaction ofcompounds3.1–3.5and3.9–3.10is much larger than that of compounds2.1–2.3. Acareful investigation on the variation between ΔH≠and ΔS≠in spirooxazine-containingcompounds and spiropyran-containing compounds has been performed and find thatΔH≠and ΔS≠have the same change trend for compounds3.1–3.5and3.9–3.10. Anisokinetic relationship, which means a linear proportionality between ΔH≠and ΔS≠, isobserved for compounds3.1–3.5and3.9–3.10. This is indicative of a commonbleaching reaction mechanism for compounds3.1–3.5and3.9–3.10.Thirdly a series of spirooxazine-and spiropyran-containing Bodipy derivatives withplatinum phosphine alkynyl linker have been designed and synthesized andcomplexes4.7and4.8have been characterized by X-ray crystallography. Theirelectrochemical, photophysical and photochromic properties are then investigated.From electrochemical and photophysical data, we can see the maximum absorptionwavelength and the oxidative wave of spirooxazine and spiropyran derivatives havean obvious change compared to the spirooxazine and spiropyran derivatives witholigoether chain and phenylacetylene linker. The result indicates there is goodconjugation between spirooxazine/spiropyran and platinum phosphine alkynyl.However, the maximum absorption wavelength and the oxidative wave of Bodipyderivatives don’t have an obvious change compared to the Bodipy derivatives witholigoether chain and phenylacetylene linker. The result suggests there is weakconjugation between Bodipy and platinum phosphine alkynyl. Photochromic reactionand the kinetics for the bleaching reaction of the ring-opened forms of complexes4.1–4.4,4.9, and4.10after excitation at355nm have been investigated in toluene byusing UV-vis absorption spectroscopy at various temperatures. By monitoring theabsorbance at650nm for complexes4.1,4.3, and4.9and640nm for complexes4.2,4.4, and4.10, the kinetics for the bleaching reactions are investigated and the rateconstants and activation parameters of complexes4.1–4.4and4.9and4.10at varioustemperatures are measured. The results show that the rate of the bleaching reaction ofcomplexes4.2,4.4, and4.10is much slower than that of complexes4.1,4.3, and4.9. A systematic investigation on the variation between ΔH≠and ΔS≠inspirooxazine-containing complexes and spiropyran-containing complexes has beenperformed and find that ΔH≠and ΔS≠have the same change trend for complexes4.1,4.3,4.9and4.2,4.4,4.10. An isokinetic relationship, which means a linearproportionality between ΔH≠and ΔS≠, is observed for complexes4.1,4.3,4.9and4.2,4.4,4.10, respectively. This is indicative of a common bleaching reaction mechanismfor complexes4.1,4.3,4.9and a common bleaching reaction mechanism forcomplexes4.2,4.4,4.11.In summary, photochromic spirooxazine-and spiropyran-containing Bodipyderivatives with different types of linker have been designed and synthesized andenergy transfer is the starting point of all my work. Their electrochemical,photophysical, and photochromic properties have also been studied. Upon addition ofTFA, the emission intensity of Bodipy is greatly quenched. This indicates efficientenergy transfer occurs from Bodipy to the ring-opened form of spirooxazine as thereis a significant spectral overlap between the absorption spectrum of the ring-openedform of spirooxazine and the emission spectrum of Bodipy. Energy transfer is furthersupported by the ultrafast transient absorption data. Upon addition of TFA, the Bodipyexcited state undergoes a faster decay and the decay time constant of the Bodipyexcited state reduces significantly. This also clearly supports the quenching of theBodipy excited state by the ring-opened merocyanine. Furthermore, the photochromicproperties of spirooxazine-and spiropyran-containing Bodipy derivatives withdifferent types of linker were studied in acetonitrile or toluene systematically. The rateconstants and activation parameters for the thermal bleaching reactions of thesecompounds were determined through kinetic studies. The result indicates kineticactivation parameters have a great effect on the rate constants of the bleachingreactions. A systematic investigation on the variation between ΔH≠and ΔS≠inspirooxazine-containing compounds and spiropyran-containing compounds have beenperformed and find that ΔH≠and ΔS≠have the same change trend for the similarstructural compounds. A common bleaching reaction mechanism for similar structural spirooxazine-containing Bodipy derivatives and a common bleaching reactionmechanism for similar structural spiropyran-containing Bodipy derivatives are alsofound. We believe that our work will provide the method for the acid-induced energytransfer system, especially for the none or weak luminescent acceptor system and givenew view for the photochromic system. These methods and views will offer theorybasis for designing novel controlled fluorescent materials and photochromic materials.