SUMMARY OF THE THESIS IN ENGLISH	
6-Alkylidenecyclohexa-2,4-dienones (o-quinone methides) have been generated by photolysis of 2-(2’-cycloalkenyl)phenols and trapped by methanol, to give ring-opened products. The best results have been obtained with the cyclohexenyl derivatives. In the case of the cyclopentenyl derivative, the photoproduct was not observed, while only small amounts of it were formed from the 7- and 8-membered ring analogues. Thus, ring size appears to be a key factor in the formation of o-quinone methides. This experimental result has been rationalized by means of DFT calculations. On the other hand, phenol substitution also appears to play a role in the process. Thus, electron withdrawing groups such as CF3 accelerate the reaction, while the opposite is true for electron donating groups such as OCH3. This is explained by an ESIPT mechanism, as the above results are consistent with the excited state acidities of the different phenols. The lack of reactivity in the case of the p-acetylphenol, where the intersystem crossing quantum yield is close to the unity, allows us to rule out a mechanism involving the triplet state.
Furthermore, the photochemical and photophysical properties of three 8-allyl-1,2,3,4-tetrahydroquinolines have been studied. These compounds exhibit a 2-allylaniline-like photochemical behavior, undergoing photocyclization to lilolidines. The absorption, emission and excitation spectra of the 8-allyl-1,2,3,4-tetrahydroquinolines, employing convenient model compounds for comparison, demonstrate the formation of a NH/pi intramolecular ground state complex (AB). This species can absorb light at long wavelengths (330-340 nm), giving rise to the corresponding excited complex AB*. Emission from AB* is red-shifted (420 nm) with respect to that observed when the monomer A is excited (excitation wavelength = 300 nm). These experimental results have been rationalized by means of density-funtional theory (DFT) calculations.
On the other hand, the 1,5-diphenyl-1,5-azapentanediyl biradical was generated by photolysis of the pyrrolidine 1,2-diphenylazacyclopentane. Among the reaction pathways followed by the biradical, C-N bond reformation with ring closure was found to be the predominating process, as determined by separate irradiation of either of the pure enantiomers of the 1,2-diphenylazacyclopentane. Disproportionation was a minor process and took only place via H abstraction by the C5 benzylic radical. Another minor pathway was C5-aryl coupling, with formation of 5-phenyl-2,3,4,5-tetrahydro-1H-benzo[b]azepine equivalent to photo-Claisen rearrangement of 1,2-diphenylazacyclopentane. Likewise, the 1,4-diphenyl-1,4-azabutanediyl biradical was generated by photolysis of the azetidine 1,2-diphenylazacyclobutane. This species underwent predominating C2-C3 cleavage, as indicated by the extensive styrene formation. Although N1-C4 bond reformation also took place, this is not the major pathway occurring from the biradical. Besides, C-4 aryl coupling to give 4-phenyl-1,2,3,4-tetrahydroquinoline was also observed. All the possible reaction pathways were theoretically studied at the UB3LYP/6-31G* computational level; the results were found to be in good agreement with the experimental observations.
In the fourth chapter we have studied the practically unexplored reactions arising from coupled PT/ET processes, compared with the well-known excited state proton transfer (PT) and electron transfer (ET) photochemical processes. A simple model (2-allyl-3-aminophenol) has been designed to address this issue by combining the known photochemistry of 2-allylphenols (AP) and 2-allylanilines (AA) in the same molecule. Thus, we have achieved a photochemical (rather than photophysical) fingerprint for the involved mechanism, provided by irreversible processes. The photocyclisation rate of 2-allyl-3-(or 5-) aminophenols is dramatically enhanced, when compared with reference compounds, as a consequence of a coupled proton/electron transfer process.