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U ovoj disertaciji predstavljeno je istraživanje fotokemije i ultrabrze dinamike kinon metida - međuprodukata sa potencijalnom primjenom u biologiji i medicini. Kinon metidi su važni međuprodukti u kemiji i fotokemiji fenola te su zanimljivi zbog svoje biološke aktivnosti i sve veće primjene u organskoj sintezi. Njihova biološka aktivnost temelji se na antiproliferativnom djelovanju zbog čega su primjenjivi u fotokemoterapiji. Upravo zbog procesa poput fotokemoterapije koji koriste biološku aktivnost kinon metida, od presudne važnosti je istraživanje puta fotokemijske reakcije njihovog nastajanja na ultrabrzim skalama. U svrhu provođenja istraživanja, na Institutu za fiziku u Zagrebu izgrađen je eksperimentalni postav za ultrabrzu tranzijentnu apsorpciju. Ostvarena je vremenska rezolucija od 200fs. Spektralni prozor probnog pulsa proteže se od 320nm do iznad 600nm što omogućava širokopojasno praćenje dinamike. Valnu duljinu pumpnog pulsa moguće je postaviti na jednu od harmonika: 267nm, 400nm, 800nm. Kao prekursori kinon metida odabrani su: adamantan fenol, adamantanski i neadamantanski derivat naftola te BODIPY-fenol. Kombiniranjem tranzijentne apsorpcije sa vremenski razlučivim mjerenjima fluorescencije te laserskom fotolizom otkriveno je kako kinon metid iz adamantan fenola nastaje u osnovnom stanju u ultrabrzoj reakciji fotodehidratacije preko konusnog presjeka sa vremenskom konstantom od 100fs. Uz stvaranje kinon metida, na različitim skalama dolazi i do stvaranja radikala i radikal kationa te tripletnog stanja prekursorske molekule. Kod derivata naftola uočeno je da se, iako molekule dijele kromoforu, reakcije uvelike razlikuju. Kod adamantan naftola, kinon metid također nastaje u osnovnom stanju fotodehidratacijom preko konusnog presjeka ali sporije, na nanosekundnoj skali, dok kod derivata naftola bez adamantanskog dijela isti nastaje nakon 40μs eliminacijom OHˑ skupine iz radikala prekursorske molekule koji nastaje ili iz radikal kationa eliminacijom protona ili iz S1 stanja prijenosom vodika. Vremenski razlučivim mjerenjima fluorescencije BODIPY-fenola potvrđena je anti-Kasha fizika uzorka. Naime, opažen je fluorescencijski pojas koji odgovara fluorescenciji iz viših pobuđenih singletnih stanja molekule iz kojih kreće reakcija stvaranja kinon metida. In this work, ultrafast photochemistry of short-lived and very reactive quinone methide intermediates is presented. Quinone methides were generated from 3 different precursors: adamantyl phenol and 2 naphthol derivatives and every photochemical reaction pathway was observed to be different. Main part of the experimental measurements was done using the ultrafast transient absorption setup built at the Institute of physics in Zagreb. Experimental setup has a possibility of wavelength choice between 800nm, 400nm, 267nm. A time resolution of 220 fs was achieved by the gradual inclusion of new experimental equipment and careful adjustments of the setup. Since for quinone methide application in chemistry, medicine or biology it is necessary to know the reaction pathway, this work’s goal was to elucidate the complete pathway of a few reactions of quinone methide generation. Experimental setup for ultrafast transient absorption at the Institute of physics opens up possibilities for further study of ultrafast photochemistry of various molecules as well as for research of a large number of interesting photoinduced processes important in chemistry, biology and medicine. Further improvement of the experimental setup can be started by connecting the homemade NOPA to the rest of the setup. In this way, it would be possible to select an excitation wavelength from spectral windows: 260-300nm and 500-670nm with a significantly shorter pulse duration of approximately 50fs. Additionally, by pumping the supercontinuum crystals with NOPA, the white light spectrum could be expanded to UV and the detection noise could be decreased with the use of cooled detectors.

Glavni cilj rada sastojao se u optimizaciji svih eksperimentalnih parametara kako bi se kroz mjerenja fotofizičkih svojstava molekula organske boje Rodamina B odredila maksimalna vremenska rezolucija eksperimentalnog postava za ultrabrzu tranzijentnu apsorpciju. Za pobudu sustava korišteni su ultrakratki laserski pulsevi stvoreni u nekolinearnom optičkom parametarskom pojačalu kućne izrade. Tranzijentno stanje se dobilo pobudivanjem molekula pomoću pumpnog pulsa valne duljine od 550 nm, dok je za probni puls, koji ispituje tranzijentno stanje, korišten superkontinuum bijele svjetlosti dobiven u pločici kalcijevog fluorida. Iz prilagodbi kinetičkih profila, tj. tranzijenata, za pojedine valne duljine od interesa na odgovarajuće modele dobiveni su parametri koji određuju vremensku rezoluciju eksperimentalnog postava što omogućuje indirektnu procjenu vremenskog trajanja pulseva koji nastaju u nekolinearnom optičkom parametarskom pojačalu. Iz mjerenja tranzijentne apsorpcije određene su vremenske rezolucije za različite postave eksperimenta, a dobivene vrijednosti kreću se u rasponu od 45 fs do 212 fs. Zaključeno je da na određivanje vremenske rezolucije utječu koherentni artefakti, prvenstveno medufazna modulacija. Ti artefakti su izraženiji za mjerenja s kraćim pulsevima pumpne zrake. Vrijeme trajanje pumpnog pulsa dodatno je provjereno mjerenjem spektralno razlučive autokorelacije pobudnog pulsa što je standardna metoda za karakterizaciju ultrabrzih (femtosekundnih) laserskih pulseva. The main goal of the thesis was to optimize all experimental parameters in order to determine the maximum time resolution of the experimental setup for ultrafast transient absorption through measurements of photophysical properties of Rhodamine B organic dye molecules. The transient state was obtained by excitation of the molecules using a pump pulse with a wavelength of 550 nm, while for the probe pulse, which examines the transient state, a white light supercontinuum obtained in a calcium fluoride plate was used. From the fitting of the kinetic profiles, ie transients, for individual wavelengths of interest to the corresponding models, parameters were obtained that determine the time resolution of the experimental setup, which allows indirect estimation of the time duration of pulses generated in noncollinear optical parameter amplifier. From the transient absorption measurements, time resolutions were determined for different experimental setups, and the values obtained ranged from 45 fs to 212 fs. It was concluded that the determination of time resolution is influenced by coherent artifacts, primarily cross-phase modulation. These artifacts are more pronounced for measurements with shorter pump beam pulses. The duration of the pump pulse was additionally checked by measuring the spectrally resolved autocorrelation of the excitation pulse, which is the standard method for the characterization of ultrafast (femtosecond) laser pulses.

U ovom diplomskom radu metodom ultrabrze tranzijentne apsorpcije proučena je ultrabrza dinamika molekule rodamina B (C28H31ClN2O3) te dvolomnost inducirana Kerr efektom u benzenu i otopini vode i acetonitrila (C2H3N). Molekule rodamina B otopljene u acetonitrilu pobudivane su femtosekundnim laserskim pulsevima valne duljine 267nm (pumpni puls) dok je njihova apsorpcija kao funkcija vremena ispitivana probnim pulsevima čiji je spektar superkontinuum generiran u kalcij-fluoridnoj (CaF2) pločici. Mjerenjima je dobiven signal koji se sastojao od pozitivnog i negativnog dijela. Pozitivan dio uzrokovan je apsorpcijom višeg stanja u koje su molekule pobudene pumpnom zrakom dok je negativan signal uzrokovan stimuliranom emisijom i izbjeljivanjem osnovnog stanja što je zaključeno promatranjem emisijske i apsorpcijske krivulje molekule rodamina B. Mjerenjem dvolomnosti inducirane Kerr efektom proučeno je trajanje te raspored spektralnih komponenti probnog pulsa u vremenu. Zaključeno je da je puls uvelike proširen u vremenu u odnosu na fundamentalni te da posjeduje pozitivan cvrkut. Uz spomenute rezultate prikazani su i superkontinuumi dobiveni u safirnoj i CaF2 pločici. Dobiveni rezultati pokazuju da je korišteni postav moguće koristiti za buduća proučavanja raznih uzoraka metodom ultrabrze tranzijentne apsorpcije. In this thesis, ultrafast dynamics of rhodamine B (C28H31ClN2O3) was studied by measuring time-resolved absorption changes using ultrafast transient absorption spectroscopy technique. In addition, birefringence induced by Kerr effect was studied in benzene and a 50:50 mixture of water and acetonitrile (C2H3N). Rhodamine B molecules dissolved in acetonitrile were excited by femtosecond pulses with the wavelength of 267nm (pump pulse) while their absorption as a function of time was tested with the probe pulses. Probe pulse spectrum was supercontinuum generated in calcium-fluoride (CaF2) crystal. Resulting signal consisted of positive and negative contribution. Positive contribution of the signal was caused by excited state absorption in which the molecules were excited by the pump beam. Negative contribution of the signal was caused by stimulated emission and ground state bleach which was concluded by observation of emission and absorption spectrum of rhodamine B. Spectral and temporal characteristics of probe pulses were studied by measurements of birefringence induced by Kerr effect. It was concluded that the probe pulses were significantly broadened in time in comparison to the fundamental pulses and also, positive chirp was present in probe pulses. In addition to above mentioned results, supercontinua generated in sapphire and CaF2 crystals were shown. Obtained results proved the functionality of the used experimental setup which will be used for future research and ultrafast transient absorption measurements of many different samples.