Electronic structure of the excited states and phenol fluorescence

Studies on m-benzyne and phenol via improved virtual orbital-complete active space configuration interaction (IVO-CASCI) analytical gradient method

“…There is an interaction between the delocalised electrons in the benzene ring and one of the lone pairs on the oxygen atom which makes the ring much more reactive than it is in benzene itself. The structure and vibrational frequencies of phenol have been the subject of many experimental [38][39][40][41] and theoretical studies [42,43].…”

General and Theoretical Aspects of Phenols

“…The experimental T 1 -S 0 transition energy was found at 28500 cm −1 , confirming that the triplet state is, in general, lower in energy than its singlet counterpart 356 . The selected optimized geometrical parameters of the lowest triplet T 1 state of phenol is displayed in Figure 27.…”

“…The fluorescent neutral S 1 state lies substantially higher in energy than T 1 and could be inhibited from quenching by the energy gap (ca 8000 cm −1 ) as well as the small one-electron spin-orbit coupling. At the anion-S 1 geometry, both singlet and triplet states of the anion are shown to be dominated by the same electronic configuration, thus allowing for a direct spin-orbit coupling 356 . As a consequence, the lifetime for fluorescence is short in the anion.…”

“…The S 1 and S 2 states belong to the A 1 and B 1 irreducible representations of the C 2v symmetry group and can be labelled as 1 L a and 1 L b , respectively. Both S 1 and S 2 excited states of PhO − were calculated to have comparable vertical energies 115,356,361 . Recent large CASPT2 computations 357,371,372 suggested an adiabatic S 1 ← S 0 energy gap of about 3.69 eV 357 .…”

“…The S 1 vibrational frequencies were also observed 153,156,169,409 and analysed in detail by means of quantum chemical computations 114,115,126,139,356,372,407,408 . Frequency shifts up to 100 cm −1 were detected for in-plane modes.…”