Excited-state relaxation properties of ionic and nonionic donor–acceptor biphenyl derivatives

A Comparative Study on the Photochemistry of Two Bipyridyl Derivatives: [2,2′‐Bipyridyl]‐3,3′‐diamine and [2,2′‐Bipyridyl]‐3,3′‐diol

“…[14] Such deactivation processes have been proposed for twisted conformations of similar compounds, such as [2,2'-bipyridyl]-3-ol [21] and derivatives of biphenyl-type systems. [22] To further explore the existence of a conical intersection, the possibility that such an approach between the S 0 and S 1 states could be located either in the reactant, intermediate, or product region should be taken into account. Considering that the TDDFT level fails to describe the charge-transfer state corresponding to the twisted conformation of the MI tautomer, we have employed the CASSCF level to explore the region where the conical intersection is expected.…”

“…However, in recent years the existence of conical intersections for biphenyl-type systems at twisted conformations has been proposed. [22] In order to check the possibility of the existence of a conical intersection in BP(OH) 2 , the same procedure described above was used. Our results show that the S 0 and S 1 states corresponding to the DE tautomer do not approach each other and show a separation of approximately 110 kcal mol…”

Excited-state relaxation of bridged and unbridged anilino-pyridinium dyes

“…The large fluorescence quantum yield of 3 can be understood by experiments on 1 at low temperature which show that the fluorescence intensity strongly increases by cooling to 140 K or 77 K (U f = 0.49 in EtOH at 140 K) [3,9]. This leads to the conclusion that 1 possesses, in contrast to the bridged compound 3, a very efficient nonradiative channel, probably linked with intramolecular twisting of the rings towards a CT state with forbidden emission properties [10].…”

“…However, low-temperature measurements of fluorescence quantum yield and lifetime are missing, and an estimation of the nature of the emitting state at low temperature cannot be characterized by its radiative rate. As the comparison of flexible and rigid compounds demonstrates the important role of intramolecular fragment rotation for quenching processes of the S 1 -state, quantum chemical estimations of the S 1 -and S 0 -state hypersurfaces using ab initio and semiempirical calculations (MNDO [5] and AM1 [9]) yield the possibility to study the formation of the S 1 twisted structure in theory (see Scheme 1a).…”

Study of the Photochemical Properties and Conical Intersections of [2,2′‐Bipyridyl]‐3‐amine‐3′‐ol

“…For BPA C H T U N G T R E N N U N G (NH 2 ) 2 this ultimately led to the localization of a CI between the ground and first singlet excited electronic states. According to several authors, [27,30,31] the existence of a twisted conformation on bipyridyl-or biphenyl-type systems indicates the presence of CIs which lead to efficient nonradiative deactivation paths of the fluorescent state. Later on we will also discuss this point for BP(OH)A C H T U N G T R E N N U N G (NH 2 ).…”