NOVELTY - A 4-(4-hydroxyphenyl)phenol derivative (I) excluding 4-(4-hydroxyphenyl)phenoxymethanesulfonic acid compound (II), is new.    USE - New 4-(4-hydroxyphenyl)phenol derivative is used as proton transport compound for proton transport material composition for electrolytic membrane for electronic device e.g. primary battery, secondary battery, fuel cell, sensor, capacitor and display apparatus (all claimed).    ADVANTAGE - The proton transport compound using the 4-(4-hydroxyphenyl)phenol derivative (I) has excellent proton transport ability and electrical storage performance, and maintains liquid crystal phase in wide temperature range.    DETAILED DESCRIPTION - A 4-(4-hydroxyphenyl)phenol derivative of formula: X-W'-Em-F'-G (I) excluding 4-(4-hydroxyphenyl)phenoxymethanesulfonic acid compound of formula (II), is new.    X=R, ROCO, or RCOO;    R=branched alkyl optionally containing unsaturated bond, where -CH2- is optionally substituted by -O-,-CO-, -COO-, -S- ,-SO- or -SO2-, and two or more non-adjacent -CH2- are substituted by -O- (optionally substituted by halo or cyano);    E=-O-, -COO-, -OCO-, -S-, -SO- or -SO2-;    m=0 or 1;    F'=-(CH2)r- (optionally substituted by halo, cyano, or methyl, ethyl or propyl (all optionally substituted by halo));    r=0-10;    G=monovalent carboxylic acid, sulfonic acid, or phosphoric acid;    W'=bivalent liquid-crystal mesogen group chosen from group of formula (i), and bivalent tetralin or bivalent polycyclic aryl (both optionally substituted);    ring A,ring B',ring C'=phenyl, cyclohexyl, cyclohexenyl, pyridinyl, pyrimidinyl, dioxin, tetralin or polycyclic aryl;    Y'=H, D, 1-8C alkyl, alkoxy, alkenyl, alkenyloxy, alkynyl, alkynyloxy, alkoxyalkyl, alkanoyloxy, alkoxycarbonyl, halo or cyano;    q1-q3=2 or more;    Z1,Z2=single bond, -CO-O-, -O-CO-, -CH2O-, -OCH2-, -CH2CH2-, -CH=CHCH2O-, -CH=CH-, -CF2O-, -OCF2-, -S-, -SO-, -SO2-, or -CC-;    p=0-2;    A'=5-18C alkylene, -C6H4-CH2-, -CO-O-(CH2)n- or -CO-;and    B"=alkylene.    INDEPENDENT CLAIMS are included for the following:    (1) proton transport material composition, which contains 2 or more types of 4-(4-hydroxyphenyl)phenol derivative (I) as proton transport compound; and    (2) electrolytic membrane, which contains 4-(4-hydroxyphenyl)phenol derivative (I) as proton transport compound or the proton transport material composition filled into through-hole of porous membrane having through-hole penetrated from surface of a film to back surface.