To improve the se
lectivity of sensing, the thermodynamics of the comp
lex formation of some ca
lix[4]arenehosts with neutra
l pheno
l guests was studied in carbon tetrach
loride as nonpo
lar so
lvent. The mo
lecu
lar shapeof ca
lixarenes was varied by the se
lective functiona
lization with
tBu and O-CH
2-Ph (O-benzy
l) or OPrgroups at the upper and
lower rim, respective
ly. To vary the e
lectron density on the guest's aromatic rings,the parent pheno
l was functiona
lized in the para position with e
lectron-withdrawing C
l, as we
ll as H, ande
lectron-re
leasing CH
3 and
tBu groups. To study the interaction between ca
lixarene and the guests, PL andquantum-chemica
l methods were app
lied. The resu
lts revea
led an overa
ll 1:1 comp
lex stoichiometry exceptfor the parent dibenzy
loxyca
lix[4]arene, where 1:2 host-guest stoichiometries were observed irrespective ofthe qua
lity of pheno
l. In the
latter case, the comp
lex formation shows a se
lf-switched character: the firstpheno
l mo
lecu
le is inc
luded in the ca
lixarene cavity, and on
ly afterward, a second guest mo
lecu
le is boundby the two benzy
loxy aromatics. A
lthough the entha
lpy change predicts strong interaction between the hostand the guest, the Gibbs free energy change of the comp
lex formation is sma
ll, resu
lting in a re
lative
ly
lowcomp
lex stabi
lity. The so
lvent-re
laxation measurements support that the unexpected entropy change cou
ld bethe consequence of the reorientation of so
lvent mo
lecu
les around the ca
lixarene bui
lding b
lock. The reorientationis assisted by dispersive forces between so
lute and so
lvent mo
lecu
les. IR and RAMAN ana
lysis of thecomp
lexes exc
lude a considerab
le participation of the pheno
lic OH group in the stabi
lization of the comp
lex.This resu
lt is in agreement with ear
lier findings where deterministic ro
le of
-
interaction in the comp
lexstabi
lity was assumed.