Intramolecular charge-transfer fluorescence

S. Tazuke and R. K. Guo, Effects of polymer microenvironment on the thermodynamics of the twisted intramolecular charge transfer fluorescence, Macromolecules 23, 719 (1990). 

K. Hamasaki, H. Ikeda, A. Nakamura, A. Ueno, F. Toda, I. Suzuki, andT. Osa, Fluorescence sensors of molecular recognition. Modified cyclodextrins capable of exhibiting guest-responsive twisted intramolecular charge transfer fluorescence, /. Am. Chem. Soc. 775,5035-5040(1993). 

In nonpolar solvents below 150°K another fluorescence than the exciplex fluorescence was observed and it was ascribed to intramolecular charge-transfer fluorescence between the dlcyano-anthracene and naphtalene moieties (34). 

Al-Hassan, K., Klein, Uwe, K. A., and Suwaiyan, A, Normal and twisted intramolecular charge-transfer fluorescence of 4-dimethylaminobenzonitrile in a-cyclodextrin cavities, Chem. Phys. Lett., 212, 581,1993. 

Setaka W, Hamada N, Kabuto C, Kira M (2005) Intramolecular charge-transfer fluorescence of l-phenyltridecamethylbicyclo[2.2.2]octasilane. Chem Commun 4666... 

Gormin D, Kasha M (1988) Triple fluorescence in aminosalicylates. Modulation of normal, proton-transfer, and twisted intramolecular charge-transfer (TICT) fluorescence by physical and chemical perturbations. Chem Phys Lett 153 574-576... 

Seo J, Kim S, Park SY (2004) Strong solvatochromic fluorescence from the intramolecular charge-transfer state created by excited-state intramolecular proton transfer. J Am Chem Soc 126 11154-11155... 

Rettig W, Lapouyade R (1994) Fluorescence probes based on twisted intramolecular charge transfer (TICT) states and other adiabatic photoreactions. Topics in fluorescence spectroscopy 4 109-149... 

Il ichev YV, Kuhnle W, Zachariasse KA (1998) Intramolecular charge transfer in dual fluorescent 4-(dialkylamino) benzonitriles. Reaction efficiency enhancement by increasing the size of the amino and benzonitrile subunits by alkyl substituents. J Phys Chem A 102(28) 5670-5680... 

Zachariasse KA, von der Haar T, Hebecker A, Leinhos U, Kuhnle W (1993) Intramolecular charge transfer in aminobenzonitriles requirements for dual fluorescence. Pure Appl Chem 65(8) 1745-1750... 

Molecular rotors are fluorophores characteristic for having a fluorescent quantum yield that strongly depends on the viscosity of the solvent [50], This property relies on the ability to resume a twisted conformation in the excited state (twisted intramolecular charge transfer or TICT state) that has a lower energy than the planar conformation. The de-excitation from the twisted conformation happens via a non-radiative pathway. Since the formation of the TICT state is favored in viscous solvents or at low temperature, the probability of fluorescence emission is reduced under those conditions [51]. Molecular rotors have been used as viscosity and flow sensors for biological applications [52], Modifications on their structure have introduced new reactivity that might increase the diversity of their use in the future [53] (see Fig. 6.7). 

Schiff bases with intramolecular charge transfer complexes such as 2,3-bis[(4-diethylamino-2-hydroxybenzylidene)amino]but-2-enedinitrile zinc (II) (BDPMB-Zn, 187) emit red fluorescence with fluorescent quantum yields up to 67%. OLEDs with a structure of ITO/TPD/ TPD BDPMB-Zn/Alq3 BDPMB-Zn/Alq3/Mg-Ag showed very bright saturated red emission with CIE (0.67, 0.32) with a luminance of 2260 cd/m2 at 20 V and a current efficiency of 0.46 cd/A (at 20 mA/cm2). In addition, the EL spectra do not change with the doping concentration in the range of 0.5—3% [229]. 

Delmond S, Letard JF, Lapouyade R et al (1996) Cation-triggered photoinduced intramolecular charge transfer and fluorescence red-shift in fluorescence probes. New J Chem 20 861-869... 

In the excited state, the redistribution of electrons can lead to localized states with distinct fluorescence spectra that are known as intramolecular charge transfer (ICT) states. This process is dynamic and coupled with dielectric relaxations in the environment [16]. This and other solvent-controlled adiabatic excited-state reactions are discussed in [17], As shown in Fig. 1, the locally excited (LE) state is populated initially upon excitation, and the ICT state appears with time in a process coupled with the reorientation of surrounding dipoles. 

Such a solvent relaxation explains the increase in the red-shift of the fluorescence spectrum as the polarity of the solvent increases. The effect of polarity on fluorescence emission will be further discussed in Chapter 7, together with polarity probes. Moreover, when a cation receptor is linked to an intramolecular charge transfer fluorophore so that the bound cation can interact with either the donor group or the acceptor group, the ICT is perturbed the consequent changes in photophysical properties of the fluorophore can be used for sensing cations (see Section 10.3.3). 

This chapter is restricted to intermolecular photophysical processes2). Intramolecular excited-state processes will not be considered here, but it should be noted that they can also affect the fluorescence characteristics intramolecular charge transfer, internal rotation (e.g. formation of twisted charge transfer states), intramolecular proton transfer, etc. 

Rettig W. and Lapouyade R. (1994) Fluorescent Probes Based on Twisted Intramolecular Charge Transfer (TICT) States and Other Adiabatic Reactions, in Lakowicz J. R. (Ed.), Topics in Fluorescence Spectroscopy, Vol. 4, Probe Design and Chemical Sensing, Plenum Press, New York, pp. 109-149. 

Intramolecular charge transfer in conjugated donor-acceptor molecules may be accompanied by internal rotation leading to TICT (twisted intramolecular charge transfer) states. A dual fluorescence may be observed as in PCT-5 (Letard et al., 1994) (which resembles the well-known DMABN (see section 3.4.4) containing a dimethylamino group instead of the monoaza-15-crown-5) the short-wavelength... 

Intramolecular charge transfer in p-anthracene-(CH2)3-p-Ar,Af-dimethylaniline (61) has been observed174 in non-polar solvents. Measurements of fluorescence-decay (by the picosecond laser method) allow some conclusions about charge-transfer dynamics in solution internal rotation is required to reach a favourable geometry for the formation of intramolecular charge-transfer between the donor (aniline) and the acceptor (anthracene). 

Figure 2,7. Absorption and fluorescence spectra of DCM-crown and its complexes with perchlorate salts in acetonitrile. DCM-H is the compound in which the crown is replaced by a hydrogen atom this compound cannot undergo intramolecular charge transfer and its fluorescence quantum yield is very low (3 x 1(C) (adapted from Ref, 40.)...

---